[RFC,net-next,v5,03/14] af_vsock: support multi-transport datagrams

  This patch adds support for multi-transport datagrams.

This includes:
- Per-packet lookup of transports when using sendto(sockaddr_vm)
- Selecting H2G or G2H transport using VMADDR_FLAG_TO_HOST and CID in
  sockaddr_vm
- rename VSOCK_TRANSPORT_F_DGRAM to VSOCK_TRANSPORT_F_DGRAM_FALLBACK
- connect() now assigns the transport for (similar to connectible
  sockets)

To preserve backwards compatibility with VMCI, some important changes
are made. The "transport_dgram" / VSOCK_TRANSPORT_F_DGRAM is changed to
be used for dgrams only if there is not yet a g2h or h2g transport that
has been registered that can transmit the packet. If there is a g2h/h2g
transport for that remote address, then that transport will be used and
not "transport_dgram". This essentially makes "transport_dgram" a
fallback transport for when h2g/g2h has not yet gone online, and so it
is renamed "transport_dgram_fallback". VMCI implements this transport.

The logic around "transport_dgram" needs to be retained to prevent
breaking VMCI:

1) VMCI datagrams existed prior to h2g/g2h and so operate under a
   different paradigm. When the vmci transport comes online, it registers
   itself with the DGRAM feature, but not H2G/G2H. Only later when the
   transport has more information about its environment does it register
   H2G or G2H.  In the case that a datagram socket is created after
   VSOCK_TRANSPORT_F_DGRAM registration but before G2H/H2G registration,
   the "transport_dgram" transport is the only registered transport and so
   needs to be used.

2) VMCI seems to require a special message be sent by the transport when a
   datagram socket calls bind(). Under the h2g/g2h model, the transport
   is selected using the remote_addr which is set by connect(). At
   bind time there is no remote_addr because often no connect() has been
   called yet: the transport is null. Therefore, with a null transport
   there doesn't seem to be any good way for a datagram socket to tell the
   VMCI transport that it has just had bind() called upon it.

With the new fallback logic, after H2G/G2H comes online the socket layer
will access the VMCI transport via transport_{h2g,g2h}. Prior to H2G/G2H
coming online, the socket layer will access the VMCI transport via
"transport_dgram_fallback".

Only transports with a special datagram fallback use-case such as VMCI
need to register VSOCK_TRANSPORT_F_DGRAM_FALLBACK.

Signed-off-by: Bobby Eshleman <bobby.eshleman@bytedance.com>
---
 drivers/vhost/vsock.c                   |  1 -
 include/linux/virtio_vsock.h            |  2 --
 include/net/af_vsock.h                  | 10 +++---
 net/vmw_vsock/af_vsock.c                | 64 ++++++++++++++++++++++++++-------
 net/vmw_vsock/hyperv_transport.c        |  6 ----
 net/vmw_vsock/virtio_transport.c        |  1 -
 net/vmw_vsock/virtio_transport_common.c |  7 ----
 net/vmw_vsock/vmci_transport.c          |  2 +-
 net/vmw_vsock/vsock_loopback.c          |  1 -
 9 files changed, 58 insertions(+), 36 deletions(-)
  

On 19.07.2023 03:50, Bobby Eshleman wrote:
> This patch adds support for multi-transport datagrams.
> 
> This includes:
> - Per-packet lookup of transports when using sendto(sockaddr_vm)
> - Selecting H2G or G2H transport using VMADDR_FLAG_TO_HOST and CID in
>   sockaddr_vm
> - rename VSOCK_TRANSPORT_F_DGRAM to VSOCK_TRANSPORT_F_DGRAM_FALLBACK
> - connect() now assigns the transport for (similar to connectible
>   sockets)
> 
> To preserve backwards compatibility with VMCI, some important changes
> are made. The "transport_dgram" / VSOCK_TRANSPORT_F_DGRAM is changed to
> be used for dgrams only if there is not yet a g2h or h2g transport that
> has been registered that can transmit the packet. If there is a g2h/h2g
> transport for that remote address, then that transport will be used and
> not "transport_dgram". This essentially makes "transport_dgram" a
> fallback transport for when h2g/g2h has not yet gone online, and so it
> is renamed "transport_dgram_fallback". VMCI implements this transport.
> 
> The logic around "transport_dgram" needs to be retained to prevent
> breaking VMCI:
> 
> 1) VMCI datagrams existed prior to h2g/g2h and so operate under a
>    different paradigm. When the vmci transport comes online, it registers
>    itself with the DGRAM feature, but not H2G/G2H. Only later when the
>    transport has more information about its environment does it register
>    H2G or G2H.  In the case that a datagram socket is created after
>    VSOCK_TRANSPORT_F_DGRAM registration but before G2H/H2G registration,
>    the "transport_dgram" transport is the only registered transport and so
>    needs to be used.
> 
> 2) VMCI seems to require a special message be sent by the transport when a
>    datagram socket calls bind(). Under the h2g/g2h model, the transport
>    is selected using the remote_addr which is set by connect(). At
>    bind time there is no remote_addr because often no connect() has been
>    called yet: the transport is null. Therefore, with a null transport
>    there doesn't seem to be any good way for a datagram socket to tell the
>    VMCI transport that it has just had bind() called upon it.
> 
> With the new fallback logic, after H2G/G2H comes online the socket layer
> will access the VMCI transport via transport_{h2g,g2h}. Prior to H2G/G2H
> coming online, the socket layer will access the VMCI transport via
> "transport_dgram_fallback".
> 
> Only transports with a special datagram fallback use-case such as VMCI
> need to register VSOCK_TRANSPORT_F_DGRAM_FALLBACK.
> 
> Signed-off-by: Bobby Eshleman <bobby.eshleman@bytedance.com>
> ---
>  drivers/vhost/vsock.c                   |  1 -
>  include/linux/virtio_vsock.h            |  2 --
>  include/net/af_vsock.h                  | 10 +++---
>  net/vmw_vsock/af_vsock.c                | 64 ++++++++++++++++++++++++++-------
>  net/vmw_vsock/hyperv_transport.c        |  6 ----
>  net/vmw_vsock/virtio_transport.c        |  1 -
>  net/vmw_vsock/virtio_transport_common.c |  7 ----
>  net/vmw_vsock/vmci_transport.c          |  2 +-
>  net/vmw_vsock/vsock_loopback.c          |  1 -
>  9 files changed, 58 insertions(+), 36 deletions(-)
> 
> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> index ae8891598a48..d5d6a3c3f273 100644
> --- a/drivers/vhost/vsock.c
> +++ b/drivers/vhost/vsock.c
> @@ -410,7 +410,6 @@ static struct virtio_transport vhost_transport = {
>  		.cancel_pkt               = vhost_transport_cancel_pkt,
>  
>  		.dgram_enqueue            = virtio_transport_dgram_enqueue,
> -		.dgram_bind               = virtio_transport_dgram_bind,
>  		.dgram_allow              = virtio_transport_dgram_allow,
>  
>  		.stream_enqueue           = virtio_transport_stream_enqueue,
> diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
> index 18cbe8d37fca..7632552bee58 100644
> --- a/include/linux/virtio_vsock.h
> +++ b/include/linux/virtio_vsock.h
> @@ -211,8 +211,6 @@ void virtio_transport_notify_buffer_size(struct vsock_sock *vsk, u64 *val);
>  u64 virtio_transport_stream_rcvhiwat(struct vsock_sock *vsk);
>  bool virtio_transport_stream_is_active(struct vsock_sock *vsk);
>  bool virtio_transport_stream_allow(u32 cid, u32 port);
> -int virtio_transport_dgram_bind(struct vsock_sock *vsk,
> -				struct sockaddr_vm *addr);
>  bool virtio_transport_dgram_allow(u32 cid, u32 port);
>  
>  int virtio_transport_connect(struct vsock_sock *vsk);
> diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
> index 305d57502e89..f6a0ca9d7c3e 100644
> --- a/include/net/af_vsock.h
> +++ b/include/net/af_vsock.h
> @@ -96,13 +96,13 @@ struct vsock_transport_send_notify_data {
>  
>  /* Transport features flags */
>  /* Transport provides host->guest communication */
> -#define VSOCK_TRANSPORT_F_H2G		0x00000001
> +#define VSOCK_TRANSPORT_F_H2G			0x00000001
>  /* Transport provides guest->host communication */
> -#define VSOCK_TRANSPORT_F_G2H		0x00000002
> -/* Transport provides DGRAM communication */
> -#define VSOCK_TRANSPORT_F_DGRAM		0x00000004
> +#define VSOCK_TRANSPORT_F_G2H			0x00000002
> +/* Transport provides fallback for DGRAM communication */
> +#define VSOCK_TRANSPORT_F_DGRAM_FALLBACK	0x00000004
>  /* Transport provides local (loopback) communication */
> -#define VSOCK_TRANSPORT_F_LOCAL		0x00000008
> +#define VSOCK_TRANSPORT_F_LOCAL			0x00000008
>  
>  struct vsock_transport {
>  	struct module *module;
> diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
> index ae5ac5531d96..26c97b33d55a 100644
> --- a/net/vmw_vsock/af_vsock.c
> +++ b/net/vmw_vsock/af_vsock.c
> @@ -139,8 +139,8 @@ struct proto vsock_proto = {
>  static const struct vsock_transport *transport_h2g;
>  /* Transport used for guest->host communication */
>  static const struct vsock_transport *transport_g2h;
> -/* Transport used for DGRAM communication */
> -static const struct vsock_transport *transport_dgram;
> +/* Transport used as a fallback for DGRAM communication */
> +static const struct vsock_transport *transport_dgram_fallback;
>  /* Transport used for local communication */
>  static const struct vsock_transport *transport_local;
>  static DEFINE_MUTEX(vsock_register_mutex);
> @@ -439,6 +439,18 @@ vsock_connectible_lookup_transport(unsigned int cid, __u8 flags)
>  	return transport;
>  }
>  
> +static const struct vsock_transport *
> +vsock_dgram_lookup_transport(unsigned int cid, __u8 flags)
> +{
> +	const struct vsock_transport *transport;
> +
> +	transport = vsock_connectible_lookup_transport(cid, flags);
> +	if (transport)
> +		return transport;
> +
> +	return transport_dgram_fallback;
> +}
> +
>  /* Assign a transport to a socket and call the .init transport callback.
>   *
>   * Note: for connection oriented socket this must be called when vsk->remote_addr
> @@ -475,7 +487,8 @@ int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk)
>  
>  	switch (sk->sk_type) {
>  	case SOCK_DGRAM:
> -		new_transport = transport_dgram;
> +		new_transport = vsock_dgram_lookup_transport(remote_cid,
> +							     remote_flags);

I'm a little bit confused about this: 
1) Let's create SOCK_DGRAM socket using vsock_create()
2) for SOCK_DGRAM it calls 'vsock_assign_transport()' and we go here, remote_cid == -1
3) I guess 'vsock_dgram_lookup_transport()' calls logic from 0002 and returns h2g for such remote cid, which is not
   correct I think...

Please correct me if i'm wrong

Thanks, Arseniy

>  		break;
>  	case SOCK_STREAM:
>  	case SOCK_SEQPACKET:
> @@ -692,6 +705,9 @@ static int __vsock_bind_connectible(struct vsock_sock *vsk,
>  static int __vsock_bind_dgram(struct vsock_sock *vsk,
>  			      struct sockaddr_vm *addr)
>  {
> +	if (!vsk->transport || !vsk->transport->dgram_bind)
> +		return -EINVAL;
> +
>  	return vsk->transport->dgram_bind(vsk, addr);
>  }
>  
> @@ -1162,6 +1178,7 @@ static int vsock_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
>  	struct vsock_sock *vsk;
>  	struct sockaddr_vm *remote_addr;
>  	const struct vsock_transport *transport;
> +	bool module_got = false;
>  
>  	if (msg->msg_flags & MSG_OOB)
>  		return -EOPNOTSUPP;
> @@ -1173,19 +1190,34 @@ static int vsock_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
>  
>  	lock_sock(sk);
>  
> -	transport = vsk->transport;
> -
>  	err = vsock_auto_bind(vsk);
>  	if (err)
>  		goto out;
>  
> -
>  	/* If the provided message contains an address, use that.  Otherwise
>  	 * fall back on the socket's remote handle (if it has been connected).
>  	 */
>  	if (msg->msg_name &&
>  	    vsock_addr_cast(msg->msg_name, msg->msg_namelen,
>  			    &remote_addr) == 0) {
> +		transport = vsock_dgram_lookup_transport(remote_addr->svm_cid,
> +							 remote_addr->svm_flags);
> +		if (!transport) {
> +			err = -EINVAL;
> +			goto out;
> +		}
> +
> +		if (!try_module_get(transport->module)) {
> +			err = -ENODEV;
> +			goto out;
> +		}
> +
> +		/* When looking up a transport dynamically and acquiring a
> +		 * reference on the module, we need to remember to release the
> +		 * reference later.
> +		 */
> +		module_got = true;
> +
>  		/* Ensure this address is of the right type and is a valid
>  		 * destination.
>  		 */
> @@ -1200,6 +1232,7 @@ static int vsock_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
>  	} else if (sock->state == SS_CONNECTED) {
>  		remote_addr = &vsk->remote_addr;
>  
> +		transport = vsk->transport;
>  		if (remote_addr->svm_cid == VMADDR_CID_ANY)
>  			remote_addr->svm_cid = transport->get_local_cid();
>  
> @@ -1224,6 +1257,8 @@ static int vsock_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
>  	err = transport->dgram_enqueue(vsk, remote_addr, msg, len);
>  
>  out:
> +	if (module_got)
> +		module_put(transport->module);
>  	release_sock(sk);
>  	return err;
>  }
> @@ -1256,13 +1291,18 @@ static int vsock_dgram_connect(struct socket *sock,
>  	if (err)
>  		goto out;
>  
> +	memcpy(&vsk->remote_addr, remote_addr, sizeof(vsk->remote_addr));
> +
> +	err = vsock_assign_transport(vsk, NULL);
> +	if (err)
> +		goto out;
> +
>  	if (!vsk->transport->dgram_allow(remote_addr->svm_cid,
>  					 remote_addr->svm_port)) {
>  		err = -EINVAL;
>  		goto out;
>  	}
>  
> -	memcpy(&vsk->remote_addr, remote_addr, sizeof(vsk->remote_addr));
>  	sock->state = SS_CONNECTED;
>  
>  	/* sock map disallows redirection of non-TCP sockets with sk_state !=
> @@ -2487,7 +2527,7 @@ int vsock_core_register(const struct vsock_transport *t, int features)
>  
>  	t_h2g = transport_h2g;
>  	t_g2h = transport_g2h;
> -	t_dgram = transport_dgram;
> +	t_dgram = transport_dgram_fallback;
>  	t_local = transport_local;
>  
>  	if (features & VSOCK_TRANSPORT_F_H2G) {
> @@ -2506,7 +2546,7 @@ int vsock_core_register(const struct vsock_transport *t, int features)
>  		t_g2h = t;
>  	}
>  
> -	if (features & VSOCK_TRANSPORT_F_DGRAM) {
> +	if (features & VSOCK_TRANSPORT_F_DGRAM_FALLBACK) {
>  		if (t_dgram) {
>  			err = -EBUSY;
>  			goto err_busy;
> @@ -2524,7 +2564,7 @@ int vsock_core_register(const struct vsock_transport *t, int features)
>  
>  	transport_h2g = t_h2g;
>  	transport_g2h = t_g2h;
> -	transport_dgram = t_dgram;
> +	transport_dgram_fallback = t_dgram;
>  	transport_local = t_local;
>  
>  err_busy:
> @@ -2543,8 +2583,8 @@ void vsock_core_unregister(const struct vsock_transport *t)
>  	if (transport_g2h == t)
>  		transport_g2h = NULL;
>  
> -	if (transport_dgram == t)
> -		transport_dgram = NULL;
> +	if (transport_dgram_fallback == t)
> +		transport_dgram_fallback = NULL;
>  
>  	if (transport_local == t)
>  		transport_local = NULL;
> diff --git a/net/vmw_vsock/hyperv_transport.c b/net/vmw_vsock/hyperv_transport.c
> index 7f1ea434656d..c29000f2612a 100644
> --- a/net/vmw_vsock/hyperv_transport.c
> +++ b/net/vmw_vsock/hyperv_transport.c
> @@ -551,11 +551,6 @@ static void hvs_destruct(struct vsock_sock *vsk)
>  	kfree(hvs);
>  }
>  
> -static int hvs_dgram_bind(struct vsock_sock *vsk, struct sockaddr_vm *addr)
> -{
> -	return -EOPNOTSUPP;
> -}
> -
>  static int hvs_dgram_enqueue(struct vsock_sock *vsk,
>  			     struct sockaddr_vm *remote, struct msghdr *msg,
>  			     size_t dgram_len)
> @@ -826,7 +821,6 @@ static struct vsock_transport hvs_transport = {
>  	.connect                  = hvs_connect,
>  	.shutdown                 = hvs_shutdown,
>  
> -	.dgram_bind               = hvs_dgram_bind,
>  	.dgram_enqueue            = hvs_dgram_enqueue,
>  	.dgram_allow              = hvs_dgram_allow,
>  
> diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
> index 66edffdbf303..ac2126c7dac5 100644
> --- a/net/vmw_vsock/virtio_transport.c
> +++ b/net/vmw_vsock/virtio_transport.c
> @@ -428,7 +428,6 @@ static struct virtio_transport virtio_transport = {
>  		.shutdown                 = virtio_transport_shutdown,
>  		.cancel_pkt               = virtio_transport_cancel_pkt,
>  
> -		.dgram_bind               = virtio_transport_dgram_bind,
>  		.dgram_enqueue            = virtio_transport_dgram_enqueue,
>  		.dgram_allow              = virtio_transport_dgram_allow,
>  
> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> index 01ea1402ad40..ffcbdd77feaa 100644
> --- a/net/vmw_vsock/virtio_transport_common.c
> +++ b/net/vmw_vsock/virtio_transport_common.c
> @@ -781,13 +781,6 @@ bool virtio_transport_stream_allow(u32 cid, u32 port)
>  }
>  EXPORT_SYMBOL_GPL(virtio_transport_stream_allow);
>  
> -int virtio_transport_dgram_bind(struct vsock_sock *vsk,
> -				struct sockaddr_vm *addr)
> -{
> -	return -EOPNOTSUPP;
> -}
> -EXPORT_SYMBOL_GPL(virtio_transport_dgram_bind);
> -
>  bool virtio_transport_dgram_allow(u32 cid, u32 port)
>  {
>  	return false;
> diff --git a/net/vmw_vsock/vmci_transport.c b/net/vmw_vsock/vmci_transport.c
> index 0bbbdb222245..857b0461f856 100644
> --- a/net/vmw_vsock/vmci_transport.c
> +++ b/net/vmw_vsock/vmci_transport.c
> @@ -2072,7 +2072,7 @@ static int __init vmci_transport_init(void)
>  	/* Register only with dgram feature, other features (H2G, G2H) will be
>  	 * registered when the first host or guest becomes active.
>  	 */
> -	err = vsock_core_register(&vmci_transport, VSOCK_TRANSPORT_F_DGRAM);
> +	err = vsock_core_register(&vmci_transport, VSOCK_TRANSPORT_F_DGRAM_FALLBACK);
>  	if (err < 0)
>  		goto err_unsubscribe;
>  
> diff --git a/net/vmw_vsock/vsock_loopback.c b/net/vmw_vsock/vsock_loopback.c
> index 2a59dd177c74..278235ea06c4 100644
> --- a/net/vmw_vsock/vsock_loopback.c
> +++ b/net/vmw_vsock/vsock_loopback.c
> @@ -61,7 +61,6 @@ static struct virtio_transport loopback_transport = {
>  		.shutdown                 = virtio_transport_shutdown,
>  		.cancel_pkt               = vsock_loopback_cancel_pkt,
>  
> -		.dgram_bind               = virtio_transport_dgram_bind,
>  		.dgram_enqueue            = virtio_transport_dgram_enqueue,
>  		.dgram_allow              = virtio_transport_dgram_allow,
>  
>
  

On Sun, Jul 23, 2023 at 12:53:15AM +0300, Arseniy Krasnov wrote:
> 
> 
> On 19.07.2023 03:50, Bobby Eshleman wrote:
> > This patch adds support for multi-transport datagrams.
> > 
> > This includes:
> > - Per-packet lookup of transports when using sendto(sockaddr_vm)
> > - Selecting H2G or G2H transport using VMADDR_FLAG_TO_HOST and CID in
> >   sockaddr_vm
> > - rename VSOCK_TRANSPORT_F_DGRAM to VSOCK_TRANSPORT_F_DGRAM_FALLBACK
> > - connect() now assigns the transport for (similar to connectible
> >   sockets)
> > 
> > To preserve backwards compatibility with VMCI, some important changes
> > are made. The "transport_dgram" / VSOCK_TRANSPORT_F_DGRAM is changed to
> > be used for dgrams only if there is not yet a g2h or h2g transport that
> > has been registered that can transmit the packet. If there is a g2h/h2g
> > transport for that remote address, then that transport will be used and
> > not "transport_dgram". This essentially makes "transport_dgram" a
> > fallback transport for when h2g/g2h has not yet gone online, and so it
> > is renamed "transport_dgram_fallback". VMCI implements this transport.
> > 
> > The logic around "transport_dgram" needs to be retained to prevent
> > breaking VMCI:
> > 
> > 1) VMCI datagrams existed prior to h2g/g2h and so operate under a
> >    different paradigm. When the vmci transport comes online, it registers
> >    itself with the DGRAM feature, but not H2G/G2H. Only later when the
> >    transport has more information about its environment does it register
> >    H2G or G2H.  In the case that a datagram socket is created after
> >    VSOCK_TRANSPORT_F_DGRAM registration but before G2H/H2G registration,
> >    the "transport_dgram" transport is the only registered transport and so
> >    needs to be used.
> > 
> > 2) VMCI seems to require a special message be sent by the transport when a
> >    datagram socket calls bind(). Under the h2g/g2h model, the transport
> >    is selected using the remote_addr which is set by connect(). At
> >    bind time there is no remote_addr because often no connect() has been
> >    called yet: the transport is null. Therefore, with a null transport
> >    there doesn't seem to be any good way for a datagram socket to tell the
> >    VMCI transport that it has just had bind() called upon it.
> > 
> > With the new fallback logic, after H2G/G2H comes online the socket layer
> > will access the VMCI transport via transport_{h2g,g2h}. Prior to H2G/G2H
> > coming online, the socket layer will access the VMCI transport via
> > "transport_dgram_fallback".
> > 
> > Only transports with a special datagram fallback use-case such as VMCI
> > need to register VSOCK_TRANSPORT_F_DGRAM_FALLBACK.
> > 
> > Signed-off-by: Bobby Eshleman <bobby.eshleman@bytedance.com>
> > ---
> >  drivers/vhost/vsock.c                   |  1 -
> >  include/linux/virtio_vsock.h            |  2 --
> >  include/net/af_vsock.h                  | 10 +++---
> >  net/vmw_vsock/af_vsock.c                | 64 ++++++++++++++++++++++++++-------
> >  net/vmw_vsock/hyperv_transport.c        |  6 ----
> >  net/vmw_vsock/virtio_transport.c        |  1 -
> >  net/vmw_vsock/virtio_transport_common.c |  7 ----
> >  net/vmw_vsock/vmci_transport.c          |  2 +-
> >  net/vmw_vsock/vsock_loopback.c          |  1 -
> >  9 files changed, 58 insertions(+), 36 deletions(-)
> > 
> > diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> > index ae8891598a48..d5d6a3c3f273 100644
> > --- a/drivers/vhost/vsock.c
> > +++ b/drivers/vhost/vsock.c
> > @@ -410,7 +410,6 @@ static struct virtio_transport vhost_transport = {
> >  		.cancel_pkt               = vhost_transport_cancel_pkt,
> >  
> >  		.dgram_enqueue            = virtio_transport_dgram_enqueue,
> > -		.dgram_bind               = virtio_transport_dgram_bind,
> >  		.dgram_allow              = virtio_transport_dgram_allow,
> >  
> >  		.stream_enqueue           = virtio_transport_stream_enqueue,
> > diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
> > index 18cbe8d37fca..7632552bee58 100644
> > --- a/include/linux/virtio_vsock.h
> > +++ b/include/linux/virtio_vsock.h
> > @@ -211,8 +211,6 @@ void virtio_transport_notify_buffer_size(struct vsock_sock *vsk, u64 *val);
> >  u64 virtio_transport_stream_rcvhiwat(struct vsock_sock *vsk);
> >  bool virtio_transport_stream_is_active(struct vsock_sock *vsk);
> >  bool virtio_transport_stream_allow(u32 cid, u32 port);
> > -int virtio_transport_dgram_bind(struct vsock_sock *vsk,
> > -				struct sockaddr_vm *addr);
> >  bool virtio_transport_dgram_allow(u32 cid, u32 port);
> >  
> >  int virtio_transport_connect(struct vsock_sock *vsk);
> > diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
> > index 305d57502e89..f6a0ca9d7c3e 100644
> > --- a/include/net/af_vsock.h
> > +++ b/include/net/af_vsock.h
> > @@ -96,13 +96,13 @@ struct vsock_transport_send_notify_data {
> >  
> >  /* Transport features flags */
> >  /* Transport provides host->guest communication */
> > -#define VSOCK_TRANSPORT_F_H2G		0x00000001
> > +#define VSOCK_TRANSPORT_F_H2G			0x00000001
> >  /* Transport provides guest->host communication */
> > -#define VSOCK_TRANSPORT_F_G2H		0x00000002
> > -/* Transport provides DGRAM communication */
> > -#define VSOCK_TRANSPORT_F_DGRAM		0x00000004
> > +#define VSOCK_TRANSPORT_F_G2H			0x00000002
> > +/* Transport provides fallback for DGRAM communication */
> > +#define VSOCK_TRANSPORT_F_DGRAM_FALLBACK	0x00000004
> >  /* Transport provides local (loopback) communication */
> > -#define VSOCK_TRANSPORT_F_LOCAL		0x00000008
> > +#define VSOCK_TRANSPORT_F_LOCAL			0x00000008
> >  
> >  struct vsock_transport {
> >  	struct module *module;
> > diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
> > index ae5ac5531d96..26c97b33d55a 100644
> > --- a/net/vmw_vsock/af_vsock.c
> > +++ b/net/vmw_vsock/af_vsock.c
> > @@ -139,8 +139,8 @@ struct proto vsock_proto = {
> >  static const struct vsock_transport *transport_h2g;
> >  /* Transport used for guest->host communication */
> >  static const struct vsock_transport *transport_g2h;
> > -/* Transport used for DGRAM communication */
> > -static const struct vsock_transport *transport_dgram;
> > +/* Transport used as a fallback for DGRAM communication */
> > +static const struct vsock_transport *transport_dgram_fallback;
> >  /* Transport used for local communication */
> >  static const struct vsock_transport *transport_local;
> >  static DEFINE_MUTEX(vsock_register_mutex);
> > @@ -439,6 +439,18 @@ vsock_connectible_lookup_transport(unsigned int cid, __u8 flags)
> >  	return transport;
> >  }
> >  
> > +static const struct vsock_transport *
> > +vsock_dgram_lookup_transport(unsigned int cid, __u8 flags)
> > +{
> > +	const struct vsock_transport *transport;
> > +
> > +	transport = vsock_connectible_lookup_transport(cid, flags);
> > +	if (transport)
> > +		return transport;
> > +
> > +	return transport_dgram_fallback;
> > +}
> > +
> >  /* Assign a transport to a socket and call the .init transport callback.
> >   *
> >   * Note: for connection oriented socket this must be called when vsk->remote_addr
> > @@ -475,7 +487,8 @@ int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk)
> >  
> >  	switch (sk->sk_type) {
> >  	case SOCK_DGRAM:
> > -		new_transport = transport_dgram;
> > +		new_transport = vsock_dgram_lookup_transport(remote_cid,
> > +							     remote_flags);
> 
> I'm a little bit confused about this: 
> 1) Let's create SOCK_DGRAM socket using vsock_create()
> 2) for SOCK_DGRAM it calls 'vsock_assign_transport()' and we go here, remote_cid == -1
> 3) I guess 'vsock_dgram_lookup_transport()' calls logic from 0002 and returns h2g for such remote cid, which is not
>    correct I think...
> 
> Please correct me if i'm wrong
> 
> Thanks, Arseniy
> 

As I understand, for the VMCI case, if transport_h2g != NULL, then
transport_h2g == transport_dgram_fallback. In either case,
vsk->transport == transport_dgram_fallback.

For the virtio/vhost case, temporarily vsk->transport == transport_h2g,
but it is unused because vsk->transport->dgram_bind == NULL.

Until SS_CONNECTED is set by connect() and vsk->transport is set
correctly, the send path is barred from using the bad transport.

I guess the recvmsg() path is a little more sketchy, and probably only
works in my test cases because h2g/g2h in the vhost/virtio case have
identical dgram_addr_init() implementations.

I think a cleaner solution is maybe checking in vsock_create() if
dgram_bind is implemented. If it is not, then vsk->transport should be
reset to NULL and a comment added explaining why VMCI requires this.

Then the other calls can begin explicitly checking for vsk->transport ==
NULL.

Thoughts?

> >  		break;
> >  	case SOCK_STREAM:
> >  	case SOCK_SEQPACKET:
> > @@ -692,6 +705,9 @@ static int __vsock_bind_connectible(struct vsock_sock *vsk,
> >  static int __vsock_bind_dgram(struct vsock_sock *vsk,
> >  			      struct sockaddr_vm *addr)
> >  {
> > +	if (!vsk->transport || !vsk->transport->dgram_bind)
> > +		return -EINVAL;
> > +
> >  	return vsk->transport->dgram_bind(vsk, addr);
> >  }
> >  
> > @@ -1162,6 +1178,7 @@ static int vsock_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
> >  	struct vsock_sock *vsk;
> >  	struct sockaddr_vm *remote_addr;
> >  	const struct vsock_transport *transport;
> > +	bool module_got = false;
> >  
> >  	if (msg->msg_flags & MSG_OOB)
> >  		return -EOPNOTSUPP;
> > @@ -1173,19 +1190,34 @@ static int vsock_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
> >  
> >  	lock_sock(sk);
> >  
> > -	transport = vsk->transport;
> > -
> >  	err = vsock_auto_bind(vsk);
> >  	if (err)
> >  		goto out;
> >  
> > -
> >  	/* If the provided message contains an address, use that.  Otherwise
> >  	 * fall back on the socket's remote handle (if it has been connected).
> >  	 */
> >  	if (msg->msg_name &&
> >  	    vsock_addr_cast(msg->msg_name, msg->msg_namelen,
> >  			    &remote_addr) == 0) {
> > +		transport = vsock_dgram_lookup_transport(remote_addr->svm_cid,
> > +							 remote_addr->svm_flags);
> > +		if (!transport) {
> > +			err = -EINVAL;
> > +			goto out;
> > +		}
> > +
> > +		if (!try_module_get(transport->module)) {
> > +			err = -ENODEV;
> > +			goto out;
> > +		}
> > +
> > +		/* When looking up a transport dynamically and acquiring a
> > +		 * reference on the module, we need to remember to release the
> > +		 * reference later.
> > +		 */
> > +		module_got = true;
> > +
> >  		/* Ensure this address is of the right type and is a valid
> >  		 * destination.
> >  		 */
> > @@ -1200,6 +1232,7 @@ static int vsock_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
> >  	} else if (sock->state == SS_CONNECTED) {
> >  		remote_addr = &vsk->remote_addr;
> >  
> > +		transport = vsk->transport;
> >  		if (remote_addr->svm_cid == VMADDR_CID_ANY)
> >  			remote_addr->svm_cid = transport->get_local_cid();
> >  
> > @@ -1224,6 +1257,8 @@ static int vsock_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
> >  	err = transport->dgram_enqueue(vsk, remote_addr, msg, len);
> >  
> >  out:
> > +	if (module_got)
> > +		module_put(transport->module);
> >  	release_sock(sk);
> >  	return err;
> >  }
> > @@ -1256,13 +1291,18 @@ static int vsock_dgram_connect(struct socket *sock,
> >  	if (err)
> >  		goto out;
> >  
> > +	memcpy(&vsk->remote_addr, remote_addr, sizeof(vsk->remote_addr));
> > +
> > +	err = vsock_assign_transport(vsk, NULL);
> > +	if (err)
> > +		goto out;
> > +
> >  	if (!vsk->transport->dgram_allow(remote_addr->svm_cid,
> >  					 remote_addr->svm_port)) {
> >  		err = -EINVAL;
> >  		goto out;
> >  	}
> >  
> > -	memcpy(&vsk->remote_addr, remote_addr, sizeof(vsk->remote_addr));
> >  	sock->state = SS_CONNECTED;
> >  
> >  	/* sock map disallows redirection of non-TCP sockets with sk_state !=
> > @@ -2487,7 +2527,7 @@ int vsock_core_register(const struct vsock_transport *t, int features)
> >  
> >  	t_h2g = transport_h2g;
> >  	t_g2h = transport_g2h;
> > -	t_dgram = transport_dgram;
> > +	t_dgram = transport_dgram_fallback;
> >  	t_local = transport_local;
> >  
> >  	if (features & VSOCK_TRANSPORT_F_H2G) {
> > @@ -2506,7 +2546,7 @@ int vsock_core_register(const struct vsock_transport *t, int features)
> >  		t_g2h = t;
> >  	}
> >  
> > -	if (features & VSOCK_TRANSPORT_F_DGRAM) {
> > +	if (features & VSOCK_TRANSPORT_F_DGRAM_FALLBACK) {
> >  		if (t_dgram) {
> >  			err = -EBUSY;
> >  			goto err_busy;
> > @@ -2524,7 +2564,7 @@ int vsock_core_register(const struct vsock_transport *t, int features)
> >  
> >  	transport_h2g = t_h2g;
> >  	transport_g2h = t_g2h;
> > -	transport_dgram = t_dgram;
> > +	transport_dgram_fallback = t_dgram;
> >  	transport_local = t_local;
> >  
> >  err_busy:
> > @@ -2543,8 +2583,8 @@ void vsock_core_unregister(const struct vsock_transport *t)
> >  	if (transport_g2h == t)
> >  		transport_g2h = NULL;
> >  
> > -	if (transport_dgram == t)
> > -		transport_dgram = NULL;
> > +	if (transport_dgram_fallback == t)
> > +		transport_dgram_fallback = NULL;
> >  
> >  	if (transport_local == t)
> >  		transport_local = NULL;
> > diff --git a/net/vmw_vsock/hyperv_transport.c b/net/vmw_vsock/hyperv_transport.c
> > index 7f1ea434656d..c29000f2612a 100644
> > --- a/net/vmw_vsock/hyperv_transport.c
> > +++ b/net/vmw_vsock/hyperv_transport.c
> > @@ -551,11 +551,6 @@ static void hvs_destruct(struct vsock_sock *vsk)
> >  	kfree(hvs);
> >  }
> >  
> > -static int hvs_dgram_bind(struct vsock_sock *vsk, struct sockaddr_vm *addr)
> > -{
> > -	return -EOPNOTSUPP;
> > -}
> > -
> >  static int hvs_dgram_enqueue(struct vsock_sock *vsk,
> >  			     struct sockaddr_vm *remote, struct msghdr *msg,
> >  			     size_t dgram_len)
> > @@ -826,7 +821,6 @@ static struct vsock_transport hvs_transport = {
> >  	.connect                  = hvs_connect,
> >  	.shutdown                 = hvs_shutdown,
> >  
> > -	.dgram_bind               = hvs_dgram_bind,
> >  	.dgram_enqueue            = hvs_dgram_enqueue,
> >  	.dgram_allow              = hvs_dgram_allow,
> >  
> > diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
> > index 66edffdbf303..ac2126c7dac5 100644
> > --- a/net/vmw_vsock/virtio_transport.c
> > +++ b/net/vmw_vsock/virtio_transport.c
> > @@ -428,7 +428,6 @@ static struct virtio_transport virtio_transport = {
> >  		.shutdown                 = virtio_transport_shutdown,
> >  		.cancel_pkt               = virtio_transport_cancel_pkt,
> >  
> > -		.dgram_bind               = virtio_transport_dgram_bind,
> >  		.dgram_enqueue            = virtio_transport_dgram_enqueue,
> >  		.dgram_allow              = virtio_transport_dgram_allow,
> >  
> > diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> > index 01ea1402ad40..ffcbdd77feaa 100644
> > --- a/net/vmw_vsock/virtio_transport_common.c
> > +++ b/net/vmw_vsock/virtio_transport_common.c
> > @@ -781,13 +781,6 @@ bool virtio_transport_stream_allow(u32 cid, u32 port)
> >  }
> >  EXPORT_SYMBOL_GPL(virtio_transport_stream_allow);
> >  
> > -int virtio_transport_dgram_bind(struct vsock_sock *vsk,
> > -				struct sockaddr_vm *addr)
> > -{
> > -	return -EOPNOTSUPP;
> > -}
> > -EXPORT_SYMBOL_GPL(virtio_transport_dgram_bind);
> > -
> >  bool virtio_transport_dgram_allow(u32 cid, u32 port)
> >  {
> >  	return false;
> > diff --git a/net/vmw_vsock/vmci_transport.c b/net/vmw_vsock/vmci_transport.c
> > index 0bbbdb222245..857b0461f856 100644
> > --- a/net/vmw_vsock/vmci_transport.c
> > +++ b/net/vmw_vsock/vmci_transport.c
> > @@ -2072,7 +2072,7 @@ static int __init vmci_transport_init(void)
> >  	/* Register only with dgram feature, other features (H2G, G2H) will be
> >  	 * registered when the first host or guest becomes active.
> >  	 */
> > -	err = vsock_core_register(&vmci_transport, VSOCK_TRANSPORT_F_DGRAM);
> > +	err = vsock_core_register(&vmci_transport, VSOCK_TRANSPORT_F_DGRAM_FALLBACK);
> >  	if (err < 0)
> >  		goto err_unsubscribe;
> >  
> > diff --git a/net/vmw_vsock/vsock_loopback.c b/net/vmw_vsock/vsock_loopback.c
> > index 2a59dd177c74..278235ea06c4 100644
> > --- a/net/vmw_vsock/vsock_loopback.c
> > +++ b/net/vmw_vsock/vsock_loopback.c
> > @@ -61,7 +61,6 @@ static struct virtio_transport loopback_transport = {
> >  		.shutdown                 = virtio_transport_shutdown,
> >  		.cancel_pkt               = vsock_loopback_cancel_pkt,
> >  
> > -		.dgram_bind               = virtio_transport_dgram_bind,
> >  		.dgram_enqueue            = virtio_transport_dgram_enqueue,
> >  		.dgram_allow              = virtio_transport_dgram_allow,
> >  
> >
  

On Wed, Aug 02, 2023 at 10:24:44PM +0000, Bobby Eshleman wrote:
> On Sun, Jul 23, 2023 at 12:53:15AM +0300, Arseniy Krasnov wrote:
> > 
> > 
> > On 19.07.2023 03:50, Bobby Eshleman wrote:
> > > This patch adds support for multi-transport datagrams.
> > > 
> > > This includes:
> > > - Per-packet lookup of transports when using sendto(sockaddr_vm)
> > > - Selecting H2G or G2H transport using VMADDR_FLAG_TO_HOST and CID in
> > >   sockaddr_vm
> > > - rename VSOCK_TRANSPORT_F_DGRAM to VSOCK_TRANSPORT_F_DGRAM_FALLBACK
> > > - connect() now assigns the transport for (similar to connectible
> > >   sockets)
> > > 
> > > To preserve backwards compatibility with VMCI, some important changes
> > > are made. The "transport_dgram" / VSOCK_TRANSPORT_F_DGRAM is changed to
> > > be used for dgrams only if there is not yet a g2h or h2g transport that
> > > has been registered that can transmit the packet. If there is a g2h/h2g
> > > transport for that remote address, then that transport will be used and
> > > not "transport_dgram". This essentially makes "transport_dgram" a
> > > fallback transport for when h2g/g2h has not yet gone online, and so it
> > > is renamed "transport_dgram_fallback". VMCI implements this transport.
> > > 
> > > The logic around "transport_dgram" needs to be retained to prevent
> > > breaking VMCI:
> > > 
> > > 1) VMCI datagrams existed prior to h2g/g2h and so operate under a
> > >    different paradigm. When the vmci transport comes online, it registers
> > >    itself with the DGRAM feature, but not H2G/G2H. Only later when the
> > >    transport has more information about its environment does it register
> > >    H2G or G2H.  In the case that a datagram socket is created after
> > >    VSOCK_TRANSPORT_F_DGRAM registration but before G2H/H2G registration,
> > >    the "transport_dgram" transport is the only registered transport and so
> > >    needs to be used.
> > > 
> > > 2) VMCI seems to require a special message be sent by the transport when a
> > >    datagram socket calls bind(). Under the h2g/g2h model, the transport
> > >    is selected using the remote_addr which is set by connect(). At
> > >    bind time there is no remote_addr because often no connect() has been
> > >    called yet: the transport is null. Therefore, with a null transport
> > >    there doesn't seem to be any good way for a datagram socket to tell the
> > >    VMCI transport that it has just had bind() called upon it.
> > > 
> > > With the new fallback logic, after H2G/G2H comes online the socket layer
> > > will access the VMCI transport via transport_{h2g,g2h}. Prior to H2G/G2H
> > > coming online, the socket layer will access the VMCI transport via
> > > "transport_dgram_fallback".
> > > 
> > > Only transports with a special datagram fallback use-case such as VMCI
> > > need to register VSOCK_TRANSPORT_F_DGRAM_FALLBACK.
> > > 
> > > Signed-off-by: Bobby Eshleman <bobby.eshleman@bytedance.com>
> > > ---
> > >  drivers/vhost/vsock.c                   |  1 -
> > >  include/linux/virtio_vsock.h            |  2 --
> > >  include/net/af_vsock.h                  | 10 +++---
> > >  net/vmw_vsock/af_vsock.c                | 64 ++++++++++++++++++++++++++-------
> > >  net/vmw_vsock/hyperv_transport.c        |  6 ----
> > >  net/vmw_vsock/virtio_transport.c        |  1 -
> > >  net/vmw_vsock/virtio_transport_common.c |  7 ----
> > >  net/vmw_vsock/vmci_transport.c          |  2 +-
> > >  net/vmw_vsock/vsock_loopback.c          |  1 -
> > >  9 files changed, 58 insertions(+), 36 deletions(-)
> > > 
> > > diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> > > index ae8891598a48..d5d6a3c3f273 100644
> > > --- a/drivers/vhost/vsock.c
> > > +++ b/drivers/vhost/vsock.c
> > > @@ -410,7 +410,6 @@ static struct virtio_transport vhost_transport = {
> > >  		.cancel_pkt               = vhost_transport_cancel_pkt,
> > >  
> > >  		.dgram_enqueue            = virtio_transport_dgram_enqueue,
> > > -		.dgram_bind               = virtio_transport_dgram_bind,
> > >  		.dgram_allow              = virtio_transport_dgram_allow,
> > >  
> > >  		.stream_enqueue           = virtio_transport_stream_enqueue,
> > > diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
> > > index 18cbe8d37fca..7632552bee58 100644
> > > --- a/include/linux/virtio_vsock.h
> > > +++ b/include/linux/virtio_vsock.h
> > > @@ -211,8 +211,6 @@ void virtio_transport_notify_buffer_size(struct vsock_sock *vsk, u64 *val);
> > >  u64 virtio_transport_stream_rcvhiwat(struct vsock_sock *vsk);
> > >  bool virtio_transport_stream_is_active(struct vsock_sock *vsk);
> > >  bool virtio_transport_stream_allow(u32 cid, u32 port);
> > > -int virtio_transport_dgram_bind(struct vsock_sock *vsk,
> > > -				struct sockaddr_vm *addr);
> > >  bool virtio_transport_dgram_allow(u32 cid, u32 port);
> > >  
> > >  int virtio_transport_connect(struct vsock_sock *vsk);
> > > diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
> > > index 305d57502e89..f6a0ca9d7c3e 100644
> > > --- a/include/net/af_vsock.h
> > > +++ b/include/net/af_vsock.h
> > > @@ -96,13 +96,13 @@ struct vsock_transport_send_notify_data {
> > >  
> > >  /* Transport features flags */
> > >  /* Transport provides host->guest communication */
> > > -#define VSOCK_TRANSPORT_F_H2G		0x00000001
> > > +#define VSOCK_TRANSPORT_F_H2G			0x00000001
> > >  /* Transport provides guest->host communication */
> > > -#define VSOCK_TRANSPORT_F_G2H		0x00000002
> > > -/* Transport provides DGRAM communication */
> > > -#define VSOCK_TRANSPORT_F_DGRAM		0x00000004
> > > +#define VSOCK_TRANSPORT_F_G2H			0x00000002
> > > +/* Transport provides fallback for DGRAM communication */
> > > +#define VSOCK_TRANSPORT_F_DGRAM_FALLBACK	0x00000004
> > >  /* Transport provides local (loopback) communication */
> > > -#define VSOCK_TRANSPORT_F_LOCAL		0x00000008
> > > +#define VSOCK_TRANSPORT_F_LOCAL			0x00000008
> > >  
> > >  struct vsock_transport {
> > >  	struct module *module;
> > > diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
> > > index ae5ac5531d96..26c97b33d55a 100644
> > > --- a/net/vmw_vsock/af_vsock.c
> > > +++ b/net/vmw_vsock/af_vsock.c
> > > @@ -139,8 +139,8 @@ struct proto vsock_proto = {
> > >  static const struct vsock_transport *transport_h2g;
> > >  /* Transport used for guest->host communication */
> > >  static const struct vsock_transport *transport_g2h;
> > > -/* Transport used for DGRAM communication */
> > > -static const struct vsock_transport *transport_dgram;
> > > +/* Transport used as a fallback for DGRAM communication */
> > > +static const struct vsock_transport *transport_dgram_fallback;
> > >  /* Transport used for local communication */
> > >  static const struct vsock_transport *transport_local;
> > >  static DEFINE_MUTEX(vsock_register_mutex);
> > > @@ -439,6 +439,18 @@ vsock_connectible_lookup_transport(unsigned int cid, __u8 flags)
> > >  	return transport;
> > >  }
> > >  
> > > +static const struct vsock_transport *
> > > +vsock_dgram_lookup_transport(unsigned int cid, __u8 flags)
> > > +{
> > > +	const struct vsock_transport *transport;
> > > +
> > > +	transport = vsock_connectible_lookup_transport(cid, flags);
> > > +	if (transport)
> > > +		return transport;
> > > +
> > > +	return transport_dgram_fallback;
> > > +}
> > > +
> > >  /* Assign a transport to a socket and call the .init transport callback.
> > >   *
> > >   * Note: for connection oriented socket this must be called when vsk->remote_addr
> > > @@ -475,7 +487,8 @@ int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk)
> > >  
> > >  	switch (sk->sk_type) {
> > >  	case SOCK_DGRAM:
> > > -		new_transport = transport_dgram;
> > > +		new_transport = vsock_dgram_lookup_transport(remote_cid,
> > > +							     remote_flags);
> > 
> > I'm a little bit confused about this: 
> > 1) Let's create SOCK_DGRAM socket using vsock_create()
> > 2) for SOCK_DGRAM it calls 'vsock_assign_transport()' and we go here, remote_cid == -1
> > 3) I guess 'vsock_dgram_lookup_transport()' calls logic from 0002 and returns h2g for such remote cid, which is not
> >    correct I think...
> > 
> > Please correct me if i'm wrong
> > 
> > Thanks, Arseniy
> > 
> 
> As I understand, for the VMCI case, if transport_h2g != NULL, then
> transport_h2g == transport_dgram_fallback. In either case,
> vsk->transport == transport_dgram_fallback.
> 
> For the virtio/vhost case, temporarily vsk->transport == transport_h2g,
> but it is unused because vsk->transport->dgram_bind == NULL.
> 
> Until SS_CONNECTED is set by connect() and vsk->transport is set
> correctly, the send path is barred from using the bad transport.
> 
> I guess the recvmsg() path is a little more sketchy, and probably only
> works in my test cases because h2g/g2h in the vhost/virtio case have
> identical dgram_addr_init() implementations.
> 
> I think a cleaner solution is maybe checking in vsock_create() if
> dgram_bind is implemented. If it is not, then vsk->transport should be
> reset to NULL and a comment added explaining why VMCI requires this.
> 
> Then the other calls can begin explicitly checking for vsk->transport ==
> NULL.

Actually, on further reflection here, in order for the vsk->transport to
be called in time for ->dgram_addr_init(), it is going to be necessary
to call vsock_assign_transport() in vsock_dgram_bind() anyway.

I think this means that the vsock_assign_transport() call can be removed
from vsock_create() call entirely, and yet VMCI can still dispatch
messages upon bind() calls as needed.

This would then simplify the whole arrangement, if there aren't other
unseen issues.

> 
> Thoughts?
> 
> > >  		break;
> > >  	case SOCK_STREAM:
> > >  	case SOCK_SEQPACKET:
> > > @@ -692,6 +705,9 @@ static int __vsock_bind_connectible(struct vsock_sock *vsk,
> > >  static int __vsock_bind_dgram(struct vsock_sock *vsk,
> > >  			      struct sockaddr_vm *addr)
> > >  {
> > > +	if (!vsk->transport || !vsk->transport->dgram_bind)
> > > +		return -EINVAL;
> > > +
> > >  	return vsk->transport->dgram_bind(vsk, addr);
> > >  }
> > >  
> > > @@ -1162,6 +1178,7 @@ static int vsock_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
> > >  	struct vsock_sock *vsk;
> > >  	struct sockaddr_vm *remote_addr;
> > >  	const struct vsock_transport *transport;
> > > +	bool module_got = false;
> > >  
> > >  	if (msg->msg_flags & MSG_OOB)
> > >  		return -EOPNOTSUPP;
> > > @@ -1173,19 +1190,34 @@ static int vsock_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
> > >  
> > >  	lock_sock(sk);
> > >  
> > > -	transport = vsk->transport;
> > > -
> > >  	err = vsock_auto_bind(vsk);
> > >  	if (err)
> > >  		goto out;
> > >  
> > > -
> > >  	/* If the provided message contains an address, use that.  Otherwise
> > >  	 * fall back on the socket's remote handle (if it has been connected).
> > >  	 */
> > >  	if (msg->msg_name &&
> > >  	    vsock_addr_cast(msg->msg_name, msg->msg_namelen,
> > >  			    &remote_addr) == 0) {
> > > +		transport = vsock_dgram_lookup_transport(remote_addr->svm_cid,
> > > +							 remote_addr->svm_flags);
> > > +		if (!transport) {
> > > +			err = -EINVAL;
> > > +			goto out;
> > > +		}
> > > +
> > > +		if (!try_module_get(transport->module)) {
> > > +			err = -ENODEV;
> > > +			goto out;
> > > +		}
> > > +
> > > +		/* When looking up a transport dynamically and acquiring a
> > > +		 * reference on the module, we need to remember to release the
> > > +		 * reference later.
> > > +		 */
> > > +		module_got = true;
> > > +
> > >  		/* Ensure this address is of the right type and is a valid
> > >  		 * destination.
> > >  		 */
> > > @@ -1200,6 +1232,7 @@ static int vsock_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
> > >  	} else if (sock->state == SS_CONNECTED) {
> > >  		remote_addr = &vsk->remote_addr;
> > >  
> > > +		transport = vsk->transport;
> > >  		if (remote_addr->svm_cid == VMADDR_CID_ANY)
> > >  			remote_addr->svm_cid = transport->get_local_cid();
> > >  
> > > @@ -1224,6 +1257,8 @@ static int vsock_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
> > >  	err = transport->dgram_enqueue(vsk, remote_addr, msg, len);
> > >  
> > >  out:
> > > +	if (module_got)
> > > +		module_put(transport->module);
> > >  	release_sock(sk);
> > >  	return err;
> > >  }
> > > @@ -1256,13 +1291,18 @@ static int vsock_dgram_connect(struct socket *sock,
> > >  	if (err)
> > >  		goto out;
> > >  
> > > +	memcpy(&vsk->remote_addr, remote_addr, sizeof(vsk->remote_addr));
> > > +
> > > +	err = vsock_assign_transport(vsk, NULL);
> > > +	if (err)
> > > +		goto out;
> > > +
> > >  	if (!vsk->transport->dgram_allow(remote_addr->svm_cid,
> > >  					 remote_addr->svm_port)) {
> > >  		err = -EINVAL;
> > >  		goto out;
> > >  	}
> > >  
> > > -	memcpy(&vsk->remote_addr, remote_addr, sizeof(vsk->remote_addr));
> > >  	sock->state = SS_CONNECTED;
> > >  
> > >  	/* sock map disallows redirection of non-TCP sockets with sk_state !=
> > > @@ -2487,7 +2527,7 @@ int vsock_core_register(const struct vsock_transport *t, int features)
> > >  
> > >  	t_h2g = transport_h2g;
> > >  	t_g2h = transport_g2h;
> > > -	t_dgram = transport_dgram;
> > > +	t_dgram = transport_dgram_fallback;
> > >  	t_local = transport_local;
> > >  
> > >  	if (features & VSOCK_TRANSPORT_F_H2G) {
> > > @@ -2506,7 +2546,7 @@ int vsock_core_register(const struct vsock_transport *t, int features)
> > >  		t_g2h = t;
> > >  	}
> > >  
> > > -	if (features & VSOCK_TRANSPORT_F_DGRAM) {
> > > +	if (features & VSOCK_TRANSPORT_F_DGRAM_FALLBACK) {
> > >  		if (t_dgram) {
> > >  			err = -EBUSY;
> > >  			goto err_busy;
> > > @@ -2524,7 +2564,7 @@ int vsock_core_register(const struct vsock_transport *t, int features)
> > >  
> > >  	transport_h2g = t_h2g;
> > >  	transport_g2h = t_g2h;
> > > -	transport_dgram = t_dgram;
> > > +	transport_dgram_fallback = t_dgram;
> > >  	transport_local = t_local;
> > >  
> > >  err_busy:
> > > @@ -2543,8 +2583,8 @@ void vsock_core_unregister(const struct vsock_transport *t)
> > >  	if (transport_g2h == t)
> > >  		transport_g2h = NULL;
> > >  
> > > -	if (transport_dgram == t)
> > > -		transport_dgram = NULL;
> > > +	if (transport_dgram_fallback == t)
> > > +		transport_dgram_fallback = NULL;
> > >  
> > >  	if (transport_local == t)
> > >  		transport_local = NULL;
> > > diff --git a/net/vmw_vsock/hyperv_transport.c b/net/vmw_vsock/hyperv_transport.c
> > > index 7f1ea434656d..c29000f2612a 100644
> > > --- a/net/vmw_vsock/hyperv_transport.c
> > > +++ b/net/vmw_vsock/hyperv_transport.c
> > > @@ -551,11 +551,6 @@ static void hvs_destruct(struct vsock_sock *vsk)
> > >  	kfree(hvs);
> > >  }
> > >  
> > > -static int hvs_dgram_bind(struct vsock_sock *vsk, struct sockaddr_vm *addr)
> > > -{
> > > -	return -EOPNOTSUPP;
> > > -}
> > > -
> > >  static int hvs_dgram_enqueue(struct vsock_sock *vsk,
> > >  			     struct sockaddr_vm *remote, struct msghdr *msg,
> > >  			     size_t dgram_len)
> > > @@ -826,7 +821,6 @@ static struct vsock_transport hvs_transport = {
> > >  	.connect                  = hvs_connect,
> > >  	.shutdown                 = hvs_shutdown,
> > >  
> > > -	.dgram_bind               = hvs_dgram_bind,
> > >  	.dgram_enqueue            = hvs_dgram_enqueue,
> > >  	.dgram_allow              = hvs_dgram_allow,
> > >  
> > > diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
> > > index 66edffdbf303..ac2126c7dac5 100644
> > > --- a/net/vmw_vsock/virtio_transport.c
> > > +++ b/net/vmw_vsock/virtio_transport.c
> > > @@ -428,7 +428,6 @@ static struct virtio_transport virtio_transport = {
> > >  		.shutdown                 = virtio_transport_shutdown,
> > >  		.cancel_pkt               = virtio_transport_cancel_pkt,
> > >  
> > > -		.dgram_bind               = virtio_transport_dgram_bind,
> > >  		.dgram_enqueue            = virtio_transport_dgram_enqueue,
> > >  		.dgram_allow              = virtio_transport_dgram_allow,
> > >  
> > > diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> > > index 01ea1402ad40..ffcbdd77feaa 100644
> > > --- a/net/vmw_vsock/virtio_transport_common.c
> > > +++ b/net/vmw_vsock/virtio_transport_common.c
> > > @@ -781,13 +781,6 @@ bool virtio_transport_stream_allow(u32 cid, u32 port)
> > >  }
> > >  EXPORT_SYMBOL_GPL(virtio_transport_stream_allow);
> > >  
> > > -int virtio_transport_dgram_bind(struct vsock_sock *vsk,
> > > -				struct sockaddr_vm *addr)
> > > -{
> > > -	return -EOPNOTSUPP;
> > > -}
> > > -EXPORT_SYMBOL_GPL(virtio_transport_dgram_bind);
> > > -
> > >  bool virtio_transport_dgram_allow(u32 cid, u32 port)
> > >  {
> > >  	return false;
> > > diff --git a/net/vmw_vsock/vmci_transport.c b/net/vmw_vsock/vmci_transport.c
> > > index 0bbbdb222245..857b0461f856 100644
> > > --- a/net/vmw_vsock/vmci_transport.c
> > > +++ b/net/vmw_vsock/vmci_transport.c
> > > @@ -2072,7 +2072,7 @@ static int __init vmci_transport_init(void)
> > >  	/* Register only with dgram feature, other features (H2G, G2H) will be
> > >  	 * registered when the first host or guest becomes active.
> > >  	 */
> > > -	err = vsock_core_register(&vmci_transport, VSOCK_TRANSPORT_F_DGRAM);
> > > +	err = vsock_core_register(&vmci_transport, VSOCK_TRANSPORT_F_DGRAM_FALLBACK);
> > >  	if (err < 0)
> > >  		goto err_unsubscribe;
> > >  
> > > diff --git a/net/vmw_vsock/vsock_loopback.c b/net/vmw_vsock/vsock_loopback.c
> > > index 2a59dd177c74..278235ea06c4 100644
> > > --- a/net/vmw_vsock/vsock_loopback.c
> > > +++ b/net/vmw_vsock/vsock_loopback.c
> > > @@ -61,7 +61,6 @@ static struct virtio_transport loopback_transport = {
> > >  		.shutdown                 = virtio_transport_shutdown,
> > >  		.cancel_pkt               = vsock_loopback_cancel_pkt,
> > >  
> > > -		.dgram_bind               = virtio_transport_dgram_bind,
> > >  		.dgram_enqueue            = virtio_transport_dgram_enqueue,
> > >  		.dgram_allow              = virtio_transport_dgram_allow,
> > >  
> > >
  

On Thu, Aug 03, 2023 at 12:53:22AM +0000, Bobby Eshleman wrote:
>On Wed, Aug 02, 2023 at 10:24:44PM +0000, Bobby Eshleman wrote:
>> On Sun, Jul 23, 2023 at 12:53:15AM +0300, Arseniy Krasnov wrote:
>> >
>> >
>> > On 19.07.2023 03:50, Bobby Eshleman wrote:
>> > > This patch adds support for multi-transport datagrams.
>> > >
>> > > This includes:
>> > > - Per-packet lookup of transports when using sendto(sockaddr_vm)
>> > > - Selecting H2G or G2H transport using VMADDR_FLAG_TO_HOST and CID in
>> > >   sockaddr_vm
>> > > - rename VSOCK_TRANSPORT_F_DGRAM to VSOCK_TRANSPORT_F_DGRAM_FALLBACK
>> > > - connect() now assigns the transport for (similar to connectible
>> > >   sockets)
>> > >
>> > > To preserve backwards compatibility with VMCI, some important changes
>> > > are made. The "transport_dgram" / VSOCK_TRANSPORT_F_DGRAM is changed to
>> > > be used for dgrams only if there is not yet a g2h or h2g transport that
>> > > has been registered that can transmit the packet. If there is a g2h/h2g
>> > > transport for that remote address, then that transport will be used and
>> > > not "transport_dgram". This essentially makes "transport_dgram" a
>> > > fallback transport for when h2g/g2h has not yet gone online, and so it
>> > > is renamed "transport_dgram_fallback". VMCI implements this transport.
>> > >
>> > > The logic around "transport_dgram" needs to be retained to prevent
>> > > breaking VMCI:
>> > >
>> > > 1) VMCI datagrams existed prior to h2g/g2h and so operate under a
>> > >    different paradigm. When the vmci transport comes online, it registers
>> > >    itself with the DGRAM feature, but not H2G/G2H. Only later when the
>> > >    transport has more information about its environment does it register
>> > >    H2G or G2H.  In the case that a datagram socket is created after
>> > >    VSOCK_TRANSPORT_F_DGRAM registration but before G2H/H2G registration,
>> > >    the "transport_dgram" transport is the only registered transport and so
>> > >    needs to be used.
>> > >
>> > > 2) VMCI seems to require a special message be sent by the transport when a
>> > >    datagram socket calls bind(). Under the h2g/g2h model, the transport
>> > >    is selected using the remote_addr which is set by connect(). At
>> > >    bind time there is no remote_addr because often no connect() has been
>> > >    called yet: the transport is null. Therefore, with a null transport
>> > >    there doesn't seem to be any good way for a datagram socket to tell the
>> > >    VMCI transport that it has just had bind() called upon it.
>> > >
>> > > With the new fallback logic, after H2G/G2H comes online the socket layer
>> > > will access the VMCI transport via transport_{h2g,g2h}. Prior to H2G/G2H
>> > > coming online, the socket layer will access the VMCI transport via
>> > > "transport_dgram_fallback".
>> > >
>> > > Only transports with a special datagram fallback use-case such as VMCI
>> > > need to register VSOCK_TRANSPORT_F_DGRAM_FALLBACK.
>> > >
>> > > Signed-off-by: Bobby Eshleman <bobby.eshleman@bytedance.com>
>> > > ---
>> > >  drivers/vhost/vsock.c                   |  1 -
>> > >  include/linux/virtio_vsock.h            |  2 --
>> > >  include/net/af_vsock.h                  | 10 +++---
>> > >  net/vmw_vsock/af_vsock.c                | 64 ++++++++++++++++++++++++++-------
>> > >  net/vmw_vsock/hyperv_transport.c        |  6 ----
>> > >  net/vmw_vsock/virtio_transport.c        |  1 -
>> > >  net/vmw_vsock/virtio_transport_common.c |  7 ----
>> > >  net/vmw_vsock/vmci_transport.c          |  2 +-
>> > >  net/vmw_vsock/vsock_loopback.c          |  1 -
>> > >  9 files changed, 58 insertions(+), 36 deletions(-)
>> > >
>> > > diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
>> > > index ae8891598a48..d5d6a3c3f273 100644
>> > > --- a/drivers/vhost/vsock.c
>> > > +++ b/drivers/vhost/vsock.c
>> > > @@ -410,7 +410,6 @@ static struct virtio_transport vhost_transport = {
>> > >  		.cancel_pkt               = vhost_transport_cancel_pkt,
>> > >
>> > >  		.dgram_enqueue            = virtio_transport_dgram_enqueue,
>> > > -		.dgram_bind               = virtio_transport_dgram_bind,
>> > >  		.dgram_allow              = virtio_transport_dgram_allow,
>> > >
>> > >  		.stream_enqueue           = virtio_transport_stream_enqueue,
>> > > diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
>> > > index 18cbe8d37fca..7632552bee58 100644
>> > > --- a/include/linux/virtio_vsock.h
>> > > +++ b/include/linux/virtio_vsock.h
>> > > @@ -211,8 +211,6 @@ void virtio_transport_notify_buffer_size(struct vsock_sock *vsk, u64 *val);
>> > >  u64 virtio_transport_stream_rcvhiwat(struct vsock_sock *vsk);
>> > >  bool virtio_transport_stream_is_active(struct vsock_sock *vsk);
>> > >  bool virtio_transport_stream_allow(u32 cid, u32 port);
>> > > -int virtio_transport_dgram_bind(struct vsock_sock *vsk,
>> > > -				struct sockaddr_vm *addr);
>> > >  bool virtio_transport_dgram_allow(u32 cid, u32 port);
>> > >
>> > >  int virtio_transport_connect(struct vsock_sock *vsk);
>> > > diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
>> > > index 305d57502e89..f6a0ca9d7c3e 100644
>> > > --- a/include/net/af_vsock.h
>> > > +++ b/include/net/af_vsock.h
>> > > @@ -96,13 +96,13 @@ struct vsock_transport_send_notify_data {
>> > >
>> > >  /* Transport features flags */
>> > >  /* Transport provides host->guest communication */
>> > > -#define VSOCK_TRANSPORT_F_H2G		0x00000001
>> > > +#define VSOCK_TRANSPORT_F_H2G			0x00000001
>> > >  /* Transport provides guest->host communication */
>> > > -#define VSOCK_TRANSPORT_F_G2H		0x00000002
>> > > -/* Transport provides DGRAM communication */
>> > > -#define VSOCK_TRANSPORT_F_DGRAM		0x00000004
>> > > +#define VSOCK_TRANSPORT_F_G2H			0x00000002
>> > > +/* Transport provides fallback for DGRAM communication */
>> > > +#define VSOCK_TRANSPORT_F_DGRAM_FALLBACK	0x00000004
>> > >  /* Transport provides local (loopback) communication */
>> > > -#define VSOCK_TRANSPORT_F_LOCAL		0x00000008
>> > > +#define VSOCK_TRANSPORT_F_LOCAL			0x00000008
>> > >
>> > >  struct vsock_transport {
>> > >  	struct module *module;
>> > > diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
>> > > index ae5ac5531d96..26c97b33d55a 100644
>> > > --- a/net/vmw_vsock/af_vsock.c
>> > > +++ b/net/vmw_vsock/af_vsock.c
>> > > @@ -139,8 +139,8 @@ struct proto vsock_proto = {
>> > >  static const struct vsock_transport *transport_h2g;
>> > >  /* Transport used for guest->host communication */
>> > >  static const struct vsock_transport *transport_g2h;
>> > > -/* Transport used for DGRAM communication */
>> > > -static const struct vsock_transport *transport_dgram;
>> > > +/* Transport used as a fallback for DGRAM communication */
>> > > +static const struct vsock_transport *transport_dgram_fallback;
>> > >  /* Transport used for local communication */
>> > >  static const struct vsock_transport *transport_local;
>> > >  static DEFINE_MUTEX(vsock_register_mutex);
>> > > @@ -439,6 +439,18 @@ vsock_connectible_lookup_transport(unsigned int cid, __u8 flags)
>> > >  	return transport;
>> > >  }
>> > >
>> > > +static const struct vsock_transport *
>> > > +vsock_dgram_lookup_transport(unsigned int cid, __u8 flags)
>> > > +{
>> > > +	const struct vsock_transport *transport;
>> > > +
>> > > +	transport = vsock_connectible_lookup_transport(cid, flags);
>> > > +	if (transport)
>> > > +		return transport;
>> > > +
>> > > +	return transport_dgram_fallback;
>> > > +}
>> > > +
>> > >  /* Assign a transport to a socket and call the .init transport callback.
>> > >   *
>> > >   * Note: for connection oriented socket this must be called when vsk->remote_addr
>> > > @@ -475,7 +487,8 @@ int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk)
>> > >
>> > >  	switch (sk->sk_type) {
>> > >  	case SOCK_DGRAM:
>> > > -		new_transport = transport_dgram;
>> > > +		new_transport = vsock_dgram_lookup_transport(remote_cid,
>> > > +							     remote_flags);
>> >
>> > I'm a little bit confused about this:
>> > 1) Let's create SOCK_DGRAM socket using vsock_create()
>> > 2) for SOCK_DGRAM it calls 'vsock_assign_transport()' and we go here, remote_cid == -1
>> > 3) I guess 'vsock_dgram_lookup_transport()' calls logic from 0002 and returns h2g for such remote cid, which is not
>> >    correct I think...
>> >
>> > Please correct me if i'm wrong
>> >
>> > Thanks, Arseniy
>> >
>>
>> As I understand, for the VMCI case, if transport_h2g != NULL, then
>> transport_h2g == transport_dgram_fallback. In either case,
>> vsk->transport == transport_dgram_fallback.
>>
>> For the virtio/vhost case, temporarily vsk->transport == transport_h2g,
>> but it is unused because vsk->transport->dgram_bind == NULL.
>>
>> Until SS_CONNECTED is set by connect() and vsk->transport is set
>> correctly, the send path is barred from using the bad transport.
>>
>> I guess the recvmsg() path is a little more sketchy, and probably only
>> works in my test cases because h2g/g2h in the vhost/virtio case have
>> identical dgram_addr_init() implementations.
>>
>> I think a cleaner solution is maybe checking in vsock_create() if
>> dgram_bind is implemented. If it is not, then vsk->transport should be
>> reset to NULL and a comment added explaining why VMCI requires this.
>>
>> Then the other calls can begin explicitly checking for vsk->transport ==
>> NULL.
>
>Actually, on further reflection here, in order for the vsk->transport to
>be called in time for ->dgram_addr_init(), it is going to be necessary
>to call vsock_assign_transport() in vsock_dgram_bind() anyway.
>
>I think this means that the vsock_assign_transport() call can be removed
>from vsock_create() call entirely, and yet VMCI can still dispatch
>messages upon bind() calls as needed.
>
>This would then simplify the whole arrangement, if there aren't other
>unseen issues.

This sounds like a good approach.

My only question is whether vsock_dgram_bind() is always called for each
dgram socket.

Stefano
  

On Thu, Aug 03, 2023 at 02:42:26PM +0200, Stefano Garzarella wrote:
> On Thu, Aug 03, 2023 at 12:53:22AM +0000, Bobby Eshleman wrote:
> > On Wed, Aug 02, 2023 at 10:24:44PM +0000, Bobby Eshleman wrote:
> > > On Sun, Jul 23, 2023 at 12:53:15AM +0300, Arseniy Krasnov wrote:
> > > >
> > > >
> > > > On 19.07.2023 03:50, Bobby Eshleman wrote:
> > > > > This patch adds support for multi-transport datagrams.
> > > > >
> > > > > This includes:
> > > > > - Per-packet lookup of transports when using sendto(sockaddr_vm)
> > > > > - Selecting H2G or G2H transport using VMADDR_FLAG_TO_HOST and CID in
> > > > >   sockaddr_vm
> > > > > - rename VSOCK_TRANSPORT_F_DGRAM to VSOCK_TRANSPORT_F_DGRAM_FALLBACK
> > > > > - connect() now assigns the transport for (similar to connectible
> > > > >   sockets)
> > > > >
> > > > > To preserve backwards compatibility with VMCI, some important changes
> > > > > are made. The "transport_dgram" / VSOCK_TRANSPORT_F_DGRAM is changed to
> > > > > be used for dgrams only if there is not yet a g2h or h2g transport that
> > > > > has been registered that can transmit the packet. If there is a g2h/h2g
> > > > > transport for that remote address, then that transport will be used and
> > > > > not "transport_dgram". This essentially makes "transport_dgram" a
> > > > > fallback transport for when h2g/g2h has not yet gone online, and so it
> > > > > is renamed "transport_dgram_fallback". VMCI implements this transport.
> > > > >
> > > > > The logic around "transport_dgram" needs to be retained to prevent
> > > > > breaking VMCI:
> > > > >
> > > > > 1) VMCI datagrams existed prior to h2g/g2h and so operate under a
> > > > >    different paradigm. When the vmci transport comes online, it registers
> > > > >    itself with the DGRAM feature, but not H2G/G2H. Only later when the
> > > > >    transport has more information about its environment does it register
> > > > >    H2G or G2H.  In the case that a datagram socket is created after
> > > > >    VSOCK_TRANSPORT_F_DGRAM registration but before G2H/H2G registration,
> > > > >    the "transport_dgram" transport is the only registered transport and so
> > > > >    needs to be used.
> > > > >
> > > > > 2) VMCI seems to require a special message be sent by the transport when a
> > > > >    datagram socket calls bind(). Under the h2g/g2h model, the transport
> > > > >    is selected using the remote_addr which is set by connect(). At
> > > > >    bind time there is no remote_addr because often no connect() has been
> > > > >    called yet: the transport is null. Therefore, with a null transport
> > > > >    there doesn't seem to be any good way for a datagram socket to tell the
> > > > >    VMCI transport that it has just had bind() called upon it.
> > > > >
> > > > > With the new fallback logic, after H2G/G2H comes online the socket layer
> > > > > will access the VMCI transport via transport_{h2g,g2h}. Prior to H2G/G2H
> > > > > coming online, the socket layer will access the VMCI transport via
> > > > > "transport_dgram_fallback".
> > > > >
> > > > > Only transports with a special datagram fallback use-case such as VMCI
> > > > > need to register VSOCK_TRANSPORT_F_DGRAM_FALLBACK.
> > > > >
> > > > > Signed-off-by: Bobby Eshleman <bobby.eshleman@bytedance.com>
> > > > > ---
> > > > >  drivers/vhost/vsock.c                   |  1 -
> > > > >  include/linux/virtio_vsock.h            |  2 --
> > > > >  include/net/af_vsock.h                  | 10 +++---
> > > > >  net/vmw_vsock/af_vsock.c                | 64 ++++++++++++++++++++++++++-------
> > > > >  net/vmw_vsock/hyperv_transport.c        |  6 ----
> > > > >  net/vmw_vsock/virtio_transport.c        |  1 -
> > > > >  net/vmw_vsock/virtio_transport_common.c |  7 ----
> > > > >  net/vmw_vsock/vmci_transport.c          |  2 +-
> > > > >  net/vmw_vsock/vsock_loopback.c          |  1 -
> > > > >  9 files changed, 58 insertions(+), 36 deletions(-)
> > > > >
> > > > > diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> > > > > index ae8891598a48..d5d6a3c3f273 100644
> > > > > --- a/drivers/vhost/vsock.c
> > > > > +++ b/drivers/vhost/vsock.c
> > > > > @@ -410,7 +410,6 @@ static struct virtio_transport vhost_transport = {
> > > > >  		.cancel_pkt               = vhost_transport_cancel_pkt,
> > > > >
> > > > >  		.dgram_enqueue            = virtio_transport_dgram_enqueue,
> > > > > -		.dgram_bind               = virtio_transport_dgram_bind,
> > > > >  		.dgram_allow              = virtio_transport_dgram_allow,
> > > > >
> > > > >  		.stream_enqueue           = virtio_transport_stream_enqueue,
> > > > > diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
> > > > > index 18cbe8d37fca..7632552bee58 100644
> > > > > --- a/include/linux/virtio_vsock.h
> > > > > +++ b/include/linux/virtio_vsock.h
> > > > > @@ -211,8 +211,6 @@ void virtio_transport_notify_buffer_size(struct vsock_sock *vsk, u64 *val);
> > > > >  u64 virtio_transport_stream_rcvhiwat(struct vsock_sock *vsk);
> > > > >  bool virtio_transport_stream_is_active(struct vsock_sock *vsk);
> > > > >  bool virtio_transport_stream_allow(u32 cid, u32 port);
> > > > > -int virtio_transport_dgram_bind(struct vsock_sock *vsk,
> > > > > -				struct sockaddr_vm *addr);
> > > > >  bool virtio_transport_dgram_allow(u32 cid, u32 port);
> > > > >
> > > > >  int virtio_transport_connect(struct vsock_sock *vsk);
> > > > > diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
> > > > > index 305d57502e89..f6a0ca9d7c3e 100644
> > > > > --- a/include/net/af_vsock.h
> > > > > +++ b/include/net/af_vsock.h
> > > > > @@ -96,13 +96,13 @@ struct vsock_transport_send_notify_data {
> > > > >
> > > > >  /* Transport features flags */
> > > > >  /* Transport provides host->guest communication */
> > > > > -#define VSOCK_TRANSPORT_F_H2G		0x00000001
> > > > > +#define VSOCK_TRANSPORT_F_H2G			0x00000001
> > > > >  /* Transport provides guest->host communication */
> > > > > -#define VSOCK_TRANSPORT_F_G2H		0x00000002
> > > > > -/* Transport provides DGRAM communication */
> > > > > -#define VSOCK_TRANSPORT_F_DGRAM		0x00000004
> > > > > +#define VSOCK_TRANSPORT_F_G2H			0x00000002
> > > > > +/* Transport provides fallback for DGRAM communication */
> > > > > +#define VSOCK_TRANSPORT_F_DGRAM_FALLBACK	0x00000004
> > > > >  /* Transport provides local (loopback) communication */
> > > > > -#define VSOCK_TRANSPORT_F_LOCAL		0x00000008
> > > > > +#define VSOCK_TRANSPORT_F_LOCAL			0x00000008
> > > > >
> > > > >  struct vsock_transport {
> > > > >  	struct module *module;
> > > > > diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
> > > > > index ae5ac5531d96..26c97b33d55a 100644
> > > > > --- a/net/vmw_vsock/af_vsock.c
> > > > > +++ b/net/vmw_vsock/af_vsock.c
> > > > > @@ -139,8 +139,8 @@ struct proto vsock_proto = {
> > > > >  static const struct vsock_transport *transport_h2g;
> > > > >  /* Transport used for guest->host communication */
> > > > >  static const struct vsock_transport *transport_g2h;
> > > > > -/* Transport used for DGRAM communication */
> > > > > -static const struct vsock_transport *transport_dgram;
> > > > > +/* Transport used as a fallback for DGRAM communication */
> > > > > +static const struct vsock_transport *transport_dgram_fallback;
> > > > >  /* Transport used for local communication */
> > > > >  static const struct vsock_transport *transport_local;
> > > > >  static DEFINE_MUTEX(vsock_register_mutex);
> > > > > @@ -439,6 +439,18 @@ vsock_connectible_lookup_transport(unsigned int cid, __u8 flags)
> > > > >  	return transport;
> > > > >  }
> > > > >
> > > > > +static const struct vsock_transport *
> > > > > +vsock_dgram_lookup_transport(unsigned int cid, __u8 flags)
> > > > > +{
> > > > > +	const struct vsock_transport *transport;
> > > > > +
> > > > > +	transport = vsock_connectible_lookup_transport(cid, flags);
> > > > > +	if (transport)
> > > > > +		return transport;
> > > > > +
> > > > > +	return transport_dgram_fallback;
> > > > > +}
> > > > > +
> > > > >  /* Assign a transport to a socket and call the .init transport callback.
> > > > >   *
> > > > >   * Note: for connection oriented socket this must be called when vsk->remote_addr
> > > > > @@ -475,7 +487,8 @@ int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk)
> > > > >
> > > > >  	switch (sk->sk_type) {
> > > > >  	case SOCK_DGRAM:
> > > > > -		new_transport = transport_dgram;
> > > > > +		new_transport = vsock_dgram_lookup_transport(remote_cid,
> > > > > +							     remote_flags);
> > > >
> > > > I'm a little bit confused about this:
> > > > 1) Let's create SOCK_DGRAM socket using vsock_create()
> > > > 2) for SOCK_DGRAM it calls 'vsock_assign_transport()' and we go here, remote_cid == -1
> > > > 3) I guess 'vsock_dgram_lookup_transport()' calls logic from 0002 and returns h2g for such remote cid, which is not
> > > >    correct I think...
> > > >
> > > > Please correct me if i'm wrong
> > > >
> > > > Thanks, Arseniy
> > > >
> > > 
> > > As I understand, for the VMCI case, if transport_h2g != NULL, then
> > > transport_h2g == transport_dgram_fallback. In either case,
> > > vsk->transport == transport_dgram_fallback.
> > > 
> > > For the virtio/vhost case, temporarily vsk->transport == transport_h2g,
> > > but it is unused because vsk->transport->dgram_bind == NULL.
> > > 
> > > Until SS_CONNECTED is set by connect() and vsk->transport is set
> > > correctly, the send path is barred from using the bad transport.
> > > 
> > > I guess the recvmsg() path is a little more sketchy, and probably only
> > > works in my test cases because h2g/g2h in the vhost/virtio case have
> > > identical dgram_addr_init() implementations.
> > > 
> > > I think a cleaner solution is maybe checking in vsock_create() if
> > > dgram_bind is implemented. If it is not, then vsk->transport should be
> > > reset to NULL and a comment added explaining why VMCI requires this.
> > > 
> > > Then the other calls can begin explicitly checking for vsk->transport ==
> > > NULL.
> > 
> > Actually, on further reflection here, in order for the vsk->transport to
> > be called in time for ->dgram_addr_init(), it is going to be necessary
> > to call vsock_assign_transport() in vsock_dgram_bind() anyway.
> > 
> > I think this means that the vsock_assign_transport() call can be removed
> > from vsock_create() call entirely, and yet VMCI can still dispatch
> > messages upon bind() calls as needed.
> > 
> > This would then simplify the whole arrangement, if there aren't other
> > unseen issues.
> 
> This sounds like a good approach.
> 
> My only question is whether vsock_dgram_bind() is always called for each
> dgram socket.
> 

No, not yet.

Currently, receivers may use vsock_dgram_recvmsg() prior to any bind,
but this should probably change.

For UDP, if we initialize a socket and call recvmsg() with no prior
bind, then the socket will be auto-bound to 0.0.0.0. I guess vsock
should probably also auto-bind in this case.

For other cases, bind may not be called prior to calls to vsock_poll() /
vsock_getname() (even if it doesn't make sense to do so), but I think it
is okay as long as vsk->transport is not used.

vsock_dgram_sendmsg() always auto-binds if needed.

> Stefano
> 
> _______________________________________________
> Virtualization mailing list
> Virtualization@lists.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/virtualization
  

On Thu, Aug 03, 2023 at 06:58:24PM +0000, Bobby Eshleman wrote:
>On Thu, Aug 03, 2023 at 02:42:26PM +0200, Stefano Garzarella wrote:
>> On Thu, Aug 03, 2023 at 12:53:22AM +0000, Bobby Eshleman wrote:
>> > On Wed, Aug 02, 2023 at 10:24:44PM +0000, Bobby Eshleman wrote:
>> > > On Sun, Jul 23, 2023 at 12:53:15AM +0300, Arseniy Krasnov wrote:
>> > > >
>> > > >
>> > > > On 19.07.2023 03:50, Bobby Eshleman wrote:
>> > > > > This patch adds support for multi-transport datagrams.
>> > > > >
>> > > > > This includes:
>> > > > > - Per-packet lookup of transports when using sendto(sockaddr_vm)
>> > > > > - Selecting H2G or G2H transport using VMADDR_FLAG_TO_HOST and CID in
>> > > > >   sockaddr_vm
>> > > > > - rename VSOCK_TRANSPORT_F_DGRAM to VSOCK_TRANSPORT_F_DGRAM_FALLBACK
>> > > > > - connect() now assigns the transport for (similar to connectible
>> > > > >   sockets)
>> > > > >
>> > > > > To preserve backwards compatibility with VMCI, some important changes
>> > > > > are made. The "transport_dgram" / VSOCK_TRANSPORT_F_DGRAM is changed to
>> > > > > be used for dgrams only if there is not yet a g2h or h2g transport that
>> > > > > has been registered that can transmit the packet. If there is a g2h/h2g
>> > > > > transport for that remote address, then that transport will be used and
>> > > > > not "transport_dgram". This essentially makes "transport_dgram" a
>> > > > > fallback transport for when h2g/g2h has not yet gone online, and so it
>> > > > > is renamed "transport_dgram_fallback". VMCI implements this transport.
>> > > > >
>> > > > > The logic around "transport_dgram" needs to be retained to prevent
>> > > > > breaking VMCI:
>> > > > >
>> > > > > 1) VMCI datagrams existed prior to h2g/g2h and so operate under a
>> > > > >    different paradigm. When the vmci transport comes online, it registers
>> > > > >    itself with the DGRAM feature, but not H2G/G2H. Only later when the
>> > > > >    transport has more information about its environment does it register
>> > > > >    H2G or G2H.  In the case that a datagram socket is created after
>> > > > >    VSOCK_TRANSPORT_F_DGRAM registration but before G2H/H2G registration,
>> > > > >    the "transport_dgram" transport is the only registered transport and so
>> > > > >    needs to be used.
>> > > > >
>> > > > > 2) VMCI seems to require a special message be sent by the transport when a
>> > > > >    datagram socket calls bind(). Under the h2g/g2h model, the transport
>> > > > >    is selected using the remote_addr which is set by connect(). At
>> > > > >    bind time there is no remote_addr because often no connect() has been
>> > > > >    called yet: the transport is null. Therefore, with a null transport
>> > > > >    there doesn't seem to be any good way for a datagram socket to tell the
>> > > > >    VMCI transport that it has just had bind() called upon it.
>> > > > >
>> > > > > With the new fallback logic, after H2G/G2H comes online the socket layer
>> > > > > will access the VMCI transport via transport_{h2g,g2h}. Prior to H2G/G2H
>> > > > > coming online, the socket layer will access the VMCI transport via
>> > > > > "transport_dgram_fallback".
>> > > > >
>> > > > > Only transports with a special datagram fallback use-case such as VMCI
>> > > > > need to register VSOCK_TRANSPORT_F_DGRAM_FALLBACK.
>> > > > >
>> > > > > Signed-off-by: Bobby Eshleman <bobby.eshleman@bytedance.com>
>> > > > > ---
>> > > > >  drivers/vhost/vsock.c                   |  1 -
>> > > > >  include/linux/virtio_vsock.h            |  2 --
>> > > > >  include/net/af_vsock.h                  | 10 +++---
>> > > > >  net/vmw_vsock/af_vsock.c                | 64 ++++++++++++++++++++++++++-------
>> > > > >  net/vmw_vsock/hyperv_transport.c        |  6 ----
>> > > > >  net/vmw_vsock/virtio_transport.c        |  1 -
>> > > > >  net/vmw_vsock/virtio_transport_common.c |  7 ----
>> > > > >  net/vmw_vsock/vmci_transport.c          |  2 +-
>> > > > >  net/vmw_vsock/vsock_loopback.c          |  1 -
>> > > > >  9 files changed, 58 insertions(+), 36 deletions(-)
>> > > > >
>> > > > > diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
>> > > > > index ae8891598a48..d5d6a3c3f273 100644
>> > > > > --- a/drivers/vhost/vsock.c
>> > > > > +++ b/drivers/vhost/vsock.c
>> > > > > @@ -410,7 +410,6 @@ static struct virtio_transport vhost_transport = {
>> > > > >  		.cancel_pkt               = vhost_transport_cancel_pkt,
>> > > > >
>> > > > >  		.dgram_enqueue            = virtio_transport_dgram_enqueue,
>> > > > > -		.dgram_bind               = virtio_transport_dgram_bind,
>> > > > >  		.dgram_allow              = virtio_transport_dgram_allow,
>> > > > >
>> > > > >  		.stream_enqueue           = virtio_transport_stream_enqueue,
>> > > > > diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
>> > > > > index 18cbe8d37fca..7632552bee58 100644
>> > > > > --- a/include/linux/virtio_vsock.h
>> > > > > +++ b/include/linux/virtio_vsock.h
>> > > > > @@ -211,8 +211,6 @@ void virtio_transport_notify_buffer_size(struct vsock_sock *vsk, u64 *val);
>> > > > >  u64 virtio_transport_stream_rcvhiwat(struct vsock_sock *vsk);
>> > > > >  bool virtio_transport_stream_is_active(struct vsock_sock *vsk);
>> > > > >  bool virtio_transport_stream_allow(u32 cid, u32 port);
>> > > > > -int virtio_transport_dgram_bind(struct vsock_sock *vsk,
>> > > > > -				struct sockaddr_vm *addr);
>> > > > >  bool virtio_transport_dgram_allow(u32 cid, u32 port);
>> > > > >
>> > > > >  int virtio_transport_connect(struct vsock_sock *vsk);
>> > > > > diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
>> > > > > index 305d57502e89..f6a0ca9d7c3e 100644
>> > > > > --- a/include/net/af_vsock.h
>> > > > > +++ b/include/net/af_vsock.h
>> > > > > @@ -96,13 +96,13 @@ struct vsock_transport_send_notify_data {
>> > > > >
>> > > > >  /* Transport features flags */
>> > > > >  /* Transport provides host->guest communication */
>> > > > > -#define VSOCK_TRANSPORT_F_H2G		0x00000001
>> > > > > +#define VSOCK_TRANSPORT_F_H2G			0x00000001
>> > > > >  /* Transport provides guest->host communication */
>> > > > > -#define VSOCK_TRANSPORT_F_G2H		0x00000002
>> > > > > -/* Transport provides DGRAM communication */
>> > > > > -#define VSOCK_TRANSPORT_F_DGRAM		0x00000004
>> > > > > +#define VSOCK_TRANSPORT_F_G2H			0x00000002
>> > > > > +/* Transport provides fallback for DGRAM communication */
>> > > > > +#define VSOCK_TRANSPORT_F_DGRAM_FALLBACK	0x00000004
>> > > > >  /* Transport provides local (loopback) communication */
>> > > > > -#define VSOCK_TRANSPORT_F_LOCAL		0x00000008
>> > > > > +#define VSOCK_TRANSPORT_F_LOCAL			0x00000008
>> > > > >
>> > > > >  struct vsock_transport {
>> > > > >  	struct module *module;
>> > > > > diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
>> > > > > index ae5ac5531d96..26c97b33d55a 100644
>> > > > > --- a/net/vmw_vsock/af_vsock.c
>> > > > > +++ b/net/vmw_vsock/af_vsock.c
>> > > > > @@ -139,8 +139,8 @@ struct proto vsock_proto = {
>> > > > >  static const struct vsock_transport *transport_h2g;
>> > > > >  /* Transport used for guest->host communication */
>> > > > >  static const struct vsock_transport *transport_g2h;
>> > > > > -/* Transport used for DGRAM communication */
>> > > > > -static const struct vsock_transport *transport_dgram;
>> > > > > +/* Transport used as a fallback for DGRAM communication */
>> > > > > +static const struct vsock_transport *transport_dgram_fallback;
>> > > > >  /* Transport used for local communication */
>> > > > >  static const struct vsock_transport *transport_local;
>> > > > >  static DEFINE_MUTEX(vsock_register_mutex);
>> > > > > @@ -439,6 +439,18 @@ vsock_connectible_lookup_transport(unsigned int cid, __u8 flags)
>> > > > >  	return transport;
>> > > > >  }
>> > > > >
>> > > > > +static const struct vsock_transport *
>> > > > > +vsock_dgram_lookup_transport(unsigned int cid, __u8 flags)
>> > > > > +{
>> > > > > +	const struct vsock_transport *transport;
>> > > > > +
>> > > > > +	transport = vsock_connectible_lookup_transport(cid, flags);
>> > > > > +	if (transport)
>> > > > > +		return transport;
>> > > > > +
>> > > > > +	return transport_dgram_fallback;
>> > > > > +}
>> > > > > +
>> > > > >  /* Assign a transport to a socket and call the .init transport callback.
>> > > > >   *
>> > > > >   * Note: for connection oriented socket this must be called when vsk->remote_addr
>> > > > > @@ -475,7 +487,8 @@ int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk)
>> > > > >
>> > > > >  	switch (sk->sk_type) {
>> > > > >  	case SOCK_DGRAM:
>> > > > > -		new_transport = transport_dgram;
>> > > > > +		new_transport = vsock_dgram_lookup_transport(remote_cid,
>> > > > > +							     remote_flags);
>> > > >
>> > > > I'm a little bit confused about this:
>> > > > 1) Let's create SOCK_DGRAM socket using vsock_create()
>> > > > 2) for SOCK_DGRAM it calls 'vsock_assign_transport()' and we go here, remote_cid == -1
>> > > > 3) I guess 'vsock_dgram_lookup_transport()' calls logic from 0002 and returns h2g for such remote cid, which is not
>> > > >    correct I think...
>> > > >
>> > > > Please correct me if i'm wrong
>> > > >
>> > > > Thanks, Arseniy
>> > > >
>> > >
>> > > As I understand, for the VMCI case, if transport_h2g != NULL, then
>> > > transport_h2g == transport_dgram_fallback. In either case,
>> > > vsk->transport == transport_dgram_fallback.
>> > >
>> > > For the virtio/vhost case, temporarily vsk->transport == transport_h2g,
>> > > but it is unused because vsk->transport->dgram_bind == NULL.
>> > >
>> > > Until SS_CONNECTED is set by connect() and vsk->transport is set
>> > > correctly, the send path is barred from using the bad transport.
>> > >
>> > > I guess the recvmsg() path is a little more sketchy, and probably only
>> > > works in my test cases because h2g/g2h in the vhost/virtio case have
>> > > identical dgram_addr_init() implementations.
>> > >
>> > > I think a cleaner solution is maybe checking in vsock_create() if
>> > > dgram_bind is implemented. If it is not, then vsk->transport should be
>> > > reset to NULL and a comment added explaining why VMCI requires this.
>> > >
>> > > Then the other calls can begin explicitly checking for vsk->transport ==
>> > > NULL.
>> >
>> > Actually, on further reflection here, in order for the vsk->transport to
>> > be called in time for ->dgram_addr_init(), it is going to be necessary
>> > to call vsock_assign_transport() in vsock_dgram_bind() anyway.
>> >
>> > I think this means that the vsock_assign_transport() call can be removed
>> > from vsock_create() call entirely, and yet VMCI can still dispatch
>> > messages upon bind() calls as needed.
>> >
>> > This would then simplify the whole arrangement, if there aren't other
>> > unseen issues.
>>
>> This sounds like a good approach.
>>
>> My only question is whether vsock_dgram_bind() is always called for each
>> dgram socket.
>>
>
>No, not yet.
>
>Currently, receivers may use vsock_dgram_recvmsg() prior to any bind,
>but this should probably change.
>
>For UDP, if we initialize a socket and call recvmsg() with no prior
>bind, then the socket will be auto-bound to 0.0.0.0. I guess vsock
>should probably also auto-bind in this case.

I see.

>
>For other cases, bind may not be called prior to calls to vsock_poll() /
>vsock_getname() (even if it doesn't make sense to do so), but I think it
>is okay as long as vsk->transport is not used.

Makes sense.

>
>vsock_dgram_sendmsg() always auto-binds if needed.

Okay, but the transport for sending messages, doesn't depend on the
local address, right?

Thanks,
Stefano
  

On Fri, Aug 04, 2023 at 04:11:58PM +0200, Stefano Garzarella wrote:
> On Thu, Aug 03, 2023 at 06:58:24PM +0000, Bobby Eshleman wrote:
> > On Thu, Aug 03, 2023 at 02:42:26PM +0200, Stefano Garzarella wrote:
> > > On Thu, Aug 03, 2023 at 12:53:22AM +0000, Bobby Eshleman wrote:
> > > > On Wed, Aug 02, 2023 at 10:24:44PM +0000, Bobby Eshleman wrote:
> > > > > On Sun, Jul 23, 2023 at 12:53:15AM +0300, Arseniy Krasnov wrote:
> > > > > >
> > > > > >
> > > > > > On 19.07.2023 03:50, Bobby Eshleman wrote:
> > > > > > > This patch adds support for multi-transport datagrams.
> > > > > > >
> > > > > > > This includes:
> > > > > > > - Per-packet lookup of transports when using sendto(sockaddr_vm)
> > > > > > > - Selecting H2G or G2H transport using VMADDR_FLAG_TO_HOST and CID in
> > > > > > >   sockaddr_vm
> > > > > > > - rename VSOCK_TRANSPORT_F_DGRAM to VSOCK_TRANSPORT_F_DGRAM_FALLBACK
> > > > > > > - connect() now assigns the transport for (similar to connectible
> > > > > > >   sockets)
> > > > > > >
> > > > > > > To preserve backwards compatibility with VMCI, some important changes
> > > > > > > are made. The "transport_dgram" / VSOCK_TRANSPORT_F_DGRAM is changed to
> > > > > > > be used for dgrams only if there is not yet a g2h or h2g transport that
> > > > > > > has been registered that can transmit the packet. If there is a g2h/h2g
> > > > > > > transport for that remote address, then that transport will be used and
> > > > > > > not "transport_dgram". This essentially makes "transport_dgram" a
> > > > > > > fallback transport for when h2g/g2h has not yet gone online, and so it
> > > > > > > is renamed "transport_dgram_fallback". VMCI implements this transport.
> > > > > > >
> > > > > > > The logic around "transport_dgram" needs to be retained to prevent
> > > > > > > breaking VMCI:
> > > > > > >
> > > > > > > 1) VMCI datagrams existed prior to h2g/g2h and so operate under a
> > > > > > >    different paradigm. When the vmci transport comes online, it registers
> > > > > > >    itself with the DGRAM feature, but not H2G/G2H. Only later when the
> > > > > > >    transport has more information about its environment does it register
> > > > > > >    H2G or G2H.  In the case that a datagram socket is created after
> > > > > > >    VSOCK_TRANSPORT_F_DGRAM registration but before G2H/H2G registration,
> > > > > > >    the "transport_dgram" transport is the only registered transport and so
> > > > > > >    needs to be used.
> > > > > > >
> > > > > > > 2) VMCI seems to require a special message be sent by the transport when a
> > > > > > >    datagram socket calls bind(). Under the h2g/g2h model, the transport
> > > > > > >    is selected using the remote_addr which is set by connect(). At
> > > > > > >    bind time there is no remote_addr because often no connect() has been
> > > > > > >    called yet: the transport is null. Therefore, with a null transport
> > > > > > >    there doesn't seem to be any good way for a datagram socket to tell the
> > > > > > >    VMCI transport that it has just had bind() called upon it.
> > > > > > >
> > > > > > > With the new fallback logic, after H2G/G2H comes online the socket layer
> > > > > > > will access the VMCI transport via transport_{h2g,g2h}. Prior to H2G/G2H
> > > > > > > coming online, the socket layer will access the VMCI transport via
> > > > > > > "transport_dgram_fallback".
> > > > > > >
> > > > > > > Only transports with a special datagram fallback use-case such as VMCI
> > > > > > > need to register VSOCK_TRANSPORT_F_DGRAM_FALLBACK.
> > > > > > >
> > > > > > > Signed-off-by: Bobby Eshleman <bobby.eshleman@bytedance.com>
> > > > > > > ---
> > > > > > >  drivers/vhost/vsock.c                   |  1 -
> > > > > > >  include/linux/virtio_vsock.h            |  2 --
> > > > > > >  include/net/af_vsock.h                  | 10 +++---
> > > > > > >  net/vmw_vsock/af_vsock.c                | 64 ++++++++++++++++++++++++++-------
> > > > > > >  net/vmw_vsock/hyperv_transport.c        |  6 ----
> > > > > > >  net/vmw_vsock/virtio_transport.c        |  1 -
> > > > > > >  net/vmw_vsock/virtio_transport_common.c |  7 ----
> > > > > > >  net/vmw_vsock/vmci_transport.c          |  2 +-
> > > > > > >  net/vmw_vsock/vsock_loopback.c          |  1 -
> > > > > > >  9 files changed, 58 insertions(+), 36 deletions(-)
> > > > > > >
> > > > > > > diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> > > > > > > index ae8891598a48..d5d6a3c3f273 100644
> > > > > > > --- a/drivers/vhost/vsock.c
> > > > > > > +++ b/drivers/vhost/vsock.c
> > > > > > > @@ -410,7 +410,6 @@ static struct virtio_transport vhost_transport = {
> > > > > > >  		.cancel_pkt               = vhost_transport_cancel_pkt,
> > > > > > >
> > > > > > >  		.dgram_enqueue            = virtio_transport_dgram_enqueue,
> > > > > > > -		.dgram_bind               = virtio_transport_dgram_bind,
> > > > > > >  		.dgram_allow              = virtio_transport_dgram_allow,
> > > > > > >
> > > > > > >  		.stream_enqueue           = virtio_transport_stream_enqueue,
> > > > > > > diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
> > > > > > > index 18cbe8d37fca..7632552bee58 100644
> > > > > > > --- a/include/linux/virtio_vsock.h
> > > > > > > +++ b/include/linux/virtio_vsock.h
> > > > > > > @@ -211,8 +211,6 @@ void virtio_transport_notify_buffer_size(struct vsock_sock *vsk, u64 *val);
> > > > > > >  u64 virtio_transport_stream_rcvhiwat(struct vsock_sock *vsk);
> > > > > > >  bool virtio_transport_stream_is_active(struct vsock_sock *vsk);
> > > > > > >  bool virtio_transport_stream_allow(u32 cid, u32 port);
> > > > > > > -int virtio_transport_dgram_bind(struct vsock_sock *vsk,
> > > > > > > -				struct sockaddr_vm *addr);
> > > > > > >  bool virtio_transport_dgram_allow(u32 cid, u32 port);
> > > > > > >
> > > > > > >  int virtio_transport_connect(struct vsock_sock *vsk);
> > > > > > > diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
> > > > > > > index 305d57502e89..f6a0ca9d7c3e 100644
> > > > > > > --- a/include/net/af_vsock.h
> > > > > > > +++ b/include/net/af_vsock.h
> > > > > > > @@ -96,13 +96,13 @@ struct vsock_transport_send_notify_data {
> > > > > > >
> > > > > > >  /* Transport features flags */
> > > > > > >  /* Transport provides host->guest communication */
> > > > > > > -#define VSOCK_TRANSPORT_F_H2G		0x00000001
> > > > > > > +#define VSOCK_TRANSPORT_F_H2G			0x00000001
> > > > > > >  /* Transport provides guest->host communication */
> > > > > > > -#define VSOCK_TRANSPORT_F_G2H		0x00000002
> > > > > > > -/* Transport provides DGRAM communication */
> > > > > > > -#define VSOCK_TRANSPORT_F_DGRAM		0x00000004
> > > > > > > +#define VSOCK_TRANSPORT_F_G2H			0x00000002
> > > > > > > +/* Transport provides fallback for DGRAM communication */
> > > > > > > +#define VSOCK_TRANSPORT_F_DGRAM_FALLBACK	0x00000004
> > > > > > >  /* Transport provides local (loopback) communication */
> > > > > > > -#define VSOCK_TRANSPORT_F_LOCAL		0x00000008
> > > > > > > +#define VSOCK_TRANSPORT_F_LOCAL			0x00000008
> > > > > > >
> > > > > > >  struct vsock_transport {
> > > > > > >  	struct module *module;
> > > > > > > diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
> > > > > > > index ae5ac5531d96..26c97b33d55a 100644
> > > > > > > --- a/net/vmw_vsock/af_vsock.c
> > > > > > > +++ b/net/vmw_vsock/af_vsock.c
> > > > > > > @@ -139,8 +139,8 @@ struct proto vsock_proto = {
> > > > > > >  static const struct vsock_transport *transport_h2g;
> > > > > > >  /* Transport used for guest->host communication */
> > > > > > >  static const struct vsock_transport *transport_g2h;
> > > > > > > -/* Transport used for DGRAM communication */
> > > > > > > -static const struct vsock_transport *transport_dgram;
> > > > > > > +/* Transport used as a fallback for DGRAM communication */
> > > > > > > +static const struct vsock_transport *transport_dgram_fallback;
> > > > > > >  /* Transport used for local communication */
> > > > > > >  static const struct vsock_transport *transport_local;
> > > > > > >  static DEFINE_MUTEX(vsock_register_mutex);
> > > > > > > @@ -439,6 +439,18 @@ vsock_connectible_lookup_transport(unsigned int cid, __u8 flags)
> > > > > > >  	return transport;
> > > > > > >  }
> > > > > > >
> > > > > > > +static const struct vsock_transport *
> > > > > > > +vsock_dgram_lookup_transport(unsigned int cid, __u8 flags)
> > > > > > > +{
> > > > > > > +	const struct vsock_transport *transport;
> > > > > > > +
> > > > > > > +	transport = vsock_connectible_lookup_transport(cid, flags);
> > > > > > > +	if (transport)
> > > > > > > +		return transport;
> > > > > > > +
> > > > > > > +	return transport_dgram_fallback;
> > > > > > > +}
> > > > > > > +
> > > > > > >  /* Assign a transport to a socket and call the .init transport callback.
> > > > > > >   *
> > > > > > >   * Note: for connection oriented socket this must be called when vsk->remote_addr
> > > > > > > @@ -475,7 +487,8 @@ int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk)
> > > > > > >
> > > > > > >  	switch (sk->sk_type) {
> > > > > > >  	case SOCK_DGRAM:
> > > > > > > -		new_transport = transport_dgram;
> > > > > > > +		new_transport = vsock_dgram_lookup_transport(remote_cid,
> > > > > > > +							     remote_flags);
> > > > > >
> > > > > > I'm a little bit confused about this:
> > > > > > 1) Let's create SOCK_DGRAM socket using vsock_create()
> > > > > > 2) for SOCK_DGRAM it calls 'vsock_assign_transport()' and we go here, remote_cid == -1
> > > > > > 3) I guess 'vsock_dgram_lookup_transport()' calls logic from 0002 and returns h2g for such remote cid, which is not
> > > > > >    correct I think...
> > > > > >
> > > > > > Please correct me if i'm wrong
> > > > > >
> > > > > > Thanks, Arseniy
> > > > > >
> > > > >
> > > > > As I understand, for the VMCI case, if transport_h2g != NULL, then
> > > > > transport_h2g == transport_dgram_fallback. In either case,
> > > > > vsk->transport == transport_dgram_fallback.
> > > > >
> > > > > For the virtio/vhost case, temporarily vsk->transport == transport_h2g,
> > > > > but it is unused because vsk->transport->dgram_bind == NULL.
> > > > >
> > > > > Until SS_CONNECTED is set by connect() and vsk->transport is set
> > > > > correctly, the send path is barred from using the bad transport.
> > > > >
> > > > > I guess the recvmsg() path is a little more sketchy, and probably only
> > > > > works in my test cases because h2g/g2h in the vhost/virtio case have
> > > > > identical dgram_addr_init() implementations.
> > > > >
> > > > > I think a cleaner solution is maybe checking in vsock_create() if
> > > > > dgram_bind is implemented. If it is not, then vsk->transport should be
> > > > > reset to NULL and a comment added explaining why VMCI requires this.
> > > > >
> > > > > Then the other calls can begin explicitly checking for vsk->transport ==
> > > > > NULL.
> > > >
> > > > Actually, on further reflection here, in order for the vsk->transport to
> > > > be called in time for ->dgram_addr_init(), it is going to be necessary
> > > > to call vsock_assign_transport() in vsock_dgram_bind() anyway.
> > > >
> > > > I think this means that the vsock_assign_transport() call can be removed
> > > > from vsock_create() call entirely, and yet VMCI can still dispatch
> > > > messages upon bind() calls as needed.
> > > >
> > > > This would then simplify the whole arrangement, if there aren't other
> > > > unseen issues.
> > > 
> > > This sounds like a good approach.
> > > 
> > > My only question is whether vsock_dgram_bind() is always called for each
> > > dgram socket.
> > > 
> > 
> > No, not yet.
> > 
> > Currently, receivers may use vsock_dgram_recvmsg() prior to any bind,
> > but this should probably change.
> > 
> > For UDP, if we initialize a socket and call recvmsg() with no prior
> > bind, then the socket will be auto-bound to 0.0.0.0. I guess vsock
> > should probably also auto-bind in this case.
> 
> I see.
> 
> > 
> > For other cases, bind may not be called prior to calls to vsock_poll() /
> > vsock_getname() (even if it doesn't make sense to do so), but I think it
> > is okay as long as vsk->transport is not used.
> 
> Makes sense.
> 
> > 
> > vsock_dgram_sendmsg() always auto-binds if needed.
> 
> Okay, but the transport for sending messages, doesn't depend on the
> local address, right?

That is correct.

Best,
Bobby