diff mbox series

[v2,1/2] erofs: update on-disk format for xattr name filter

Message ID 20230705070427.92579-2-jefflexu@linux.alibaba.com
State New
Headers
Series erofs: introduce xattr name bloom filter |

Commit Message

Jingbo Xu July 5, 2023, 7:04 a.m. UTC 
  The xattr name bloom filter feature is going to be introduced to speed
up the negative xattr lookup, e.g. system.posix_acl_[access|default]
lookup when running "ls -lR" workload.

The number of common used extended attributes (n) is approximately 30.

	trusted.overlay.opaque
	trusted.overlay.redirect
	trusted.overlay.origin
	trusted.overlay.impure
	trusted.overlay.nlink
	trusted.overlay.upper
	trusted.overlay.metacopy
	trusted.overlay.protattr
	user.overlay.opaque
	user.overlay.redirect
	user.overlay.origin
	user.overlay.impure
	user.overlay.nlink
	user.overlay.upper
	user.overlay.metacopy
	user.overlay.protattr
	security.evm
	security.ima
	security.selinux
	security.SMACK64
	security.SMACK64IPIN
	security.SMACK64IPOUT
	security.SMACK64EXEC
	security.SMACK64TRANSMUTE
	security.SMACK64MMAP
	security.apparmor
	security.capability
	system.posix_acl_access
	system.posix_acl_default
	user.mime_type

Given the number of bits of the bloom filter (m) is 32, the optimal
value for the number of the hash functions (k) is 1 (ln2 * m/n = 0.74).

The single hash function is implemented as:

	xxh32(name, strlen(name), EROFS_XATTR_FILTER_SEED + index)

where index represents the index of corresponding predefined short name
prefix, while name represents the name string after stripping the above
predefined name prefix.

The constant magic number EROFS_XATTR_FILTER_SEED, i.e. 0x25BBE08F, is
used to give a better spread when mapping these 30 extended attributes
into 32-bit bloom filter as:

	bit  0: security.ima
	bit  1:
	bit  2: trusted.overlay.nlink
	bit  3:
	bit  4: user.overlay.nlink
	bit  5: trusted.overlay.upper
	bit  6: user.overlay.origin
	bit  7: trusted.overlay.protattr
	bit  8: security.apparmor
	bit  9: user.overlay.protattr
	bit 10: user.overlay.opaque
	bit 11: security.selinux
	bit 12: security.SMACK64TRANSMUTE
	bit 13: security.SMACK64
	bit 14: security.SMACK64MMAP
	bit 15: user.overlay.impure
	bit 16: security.SMACK64IPIN
	bit 17: trusted.overlay.redirect
	bit 18: trusted.overlay.origin
	bit 19: security.SMACK64IPOUT
	bit 20: trusted.overlay.opaque
	bit 21: system.posix_acl_default
	bit 22:
	bit 23: user.mime_type
	bit 24: trusted.overlay.impure
	bit 25: security.SMACK64EXEC
	bit 26: user.overlay.redirect
	bit 27: user.overlay.upper
	bit 28: security.evm
	bit 29: security.capability
	bit 30: system.posix_acl_access
	bit 31: trusted.overlay.metacopy, user.overlay.metacopy

The h_name_filter field is introduced to the on-disk per-inode xattr
header to place the corresponding xattr name filter, where bit value 1
indicates non-existence for compatibility.

This feature is indicated by EROFS_FEATURE_COMPAT_XATTR_FILTER
compatible feature bit.

Suggested-by: Alexander Larsson <alexl@redhat.com>
Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
---
 fs/erofs/erofs_fs.h | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

Comments

Gao Xiang July 5, 2023, 7:24 a.m. UTC | #1 
On 2023/7/5 15:04, Jingbo Xu wrote:
> The xattr name bloom filter feature is going to be introduced to speed
> up the negative xattr lookup, e.g. system.posix_acl_[access|default]
> lookup when running "ls -lR" workload.
> 
> The number of common used extended attributes (n) is approximately 30.

There are some commonly used extended attributes (n) and the total number
of these is 31:

> 
> 	trusted.overlay.opaque
> 	trusted.overlay.redirect
> 	trusted.overlay.origin
> 	trusted.overlay.impure
> 	trusted.overlay.nlink
> 	trusted.overlay.upper
> 	trusted.overlay.metacopy
> 	trusted.overlay.protattr
> 	user.overlay.opaque
> 	user.overlay.redirect
> 	user.overlay.origin
> 	user.overlay.impure
> 	user.overlay.nlink
> 	user.overlay.upper
> 	user.overlay.metacopy
> 	user.overlay.protattr
> 	security.evm
> 	security.ima
> 	security.selinux
> 	security.SMACK64
> 	security.SMACK64IPIN
> 	security.SMACK64IPOUT
> 	security.SMACK64EXEC
> 	security.SMACK64TRANSMUTE
> 	security.SMACK64MMAP
> 	security.apparmor
> 	security.capability
> 	system.posix_acl_access
> 	system.posix_acl_default
> 	user.mime_type
> 
> Given the number of bits of the bloom filter (m) is 32, the optimal
> value for the number of the hash functions (k) is 1 (ln2 * m/n = 0.74).
> 
> The single hash function is implemented as:
> 
> 	xxh32(name, strlen(name), EROFS_XATTR_FILTER_SEED + index)
> 
> where index represents the index of corresponding predefined short name

where `index`...



> prefix, while name represents the name string after stripping the above
> predefined name prefix.
> 
> The constant magic number EROFS_XATTR_FILTER_SEED, i.e. 0x25BBE08F, is
> used to give a better spread when mapping these 30 extended attributes
> into 32-bit bloom filter as:
> 
> 	bit  0: security.ima
> 	bit  1:
> 	bit  2: trusted.overlay.nlink
> 	bit  3:
> 	bit  4: user.overlay.nlink
> 	bit  5: trusted.overlay.upper
> 	bit  6: user.overlay.origin
> 	bit  7: trusted.overlay.protattr
> 	bit  8: security.apparmor
> 	bit  9: user.overlay.protattr
> 	bit 10: user.overlay.opaque
> 	bit 11: security.selinux
> 	bit 12: security.SMACK64TRANSMUTE
> 	bit 13: security.SMACK64
> 	bit 14: security.SMACK64MMAP
> 	bit 15: user.overlay.impure
> 	bit 16: security.SMACK64IPIN
> 	bit 17: trusted.overlay.redirect
> 	bit 18: trusted.overlay.origin
> 	bit 19: security.SMACK64IPOUT
> 	bit 20: trusted.overlay.opaque
> 	bit 21: system.posix_acl_default
> 	bit 22:
> 	bit 23: user.mime_type
> 	bit 24: trusted.overlay.impure
> 	bit 25: security.SMACK64EXEC
> 	bit 26: user.overlay.redirect
> 	bit 27: user.overlay.upper
> 	bit 28: security.evm
> 	bit 29: security.capability
> 	bit 30: system.posix_acl_access
> 	bit 31: trusted.overlay.metacopy, user.overlay.metacopy
> 
> The h_name_filter field is introduced to the on-disk per-inode xattr
> header to place the corresponding xattr name filter, where bit value 1
> indicates non-existence for compatibility.
> 
> This feature is indicated by EROFS_FEATURE_COMPAT_XATTR_FILTER
> compatible feature bit.
> 
> Suggested-by: Alexander Larsson <alexl@redhat.com>
> Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
> ---
>   fs/erofs/erofs_fs.h | 8 +++++++-
>   1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/erofs/erofs_fs.h b/fs/erofs/erofs_fs.h
> index 2c7b16e340fe..b4b6235fd720 100644
> --- a/fs/erofs/erofs_fs.h
> +++ b/fs/erofs/erofs_fs.h
> @@ -13,6 +13,7 @@
>   
>   #define EROFS_FEATURE_COMPAT_SB_CHKSUM          0x00000001
>   #define EROFS_FEATURE_COMPAT_MTIME              0x00000002
> +#define EROFS_FEATURE_COMPAT_XATTR_FILTER	0x00000004

I'd suggest that if we could leave one reserved byte in the
superblock for now (and checking if it's 0) since
   1) xattr filter feature is a compatible feature;
   2) I'm not sure if the implementation could be changed.

so that later implementation changes won't bother compat bits
again.

>   
>   /*
>    * Any bits that aren't in EROFS_ALL_FEATURE_INCOMPAT should
> @@ -200,7 +201,7 @@ struct erofs_inode_extended {
>    * for read-only fs, no need to introduce h_refcount
>    */
>   struct erofs_xattr_ibody_header {
> -	__le32 h_reserved;
> +	__le32 h_name_filter;		/* bit value 1 indicates not-present */
>   	__u8   h_shared_count;
>   	__u8   h_reserved2[7];
>   	__le32 h_shared_xattrs[];       /* shared xattr id array */
> @@ -221,6 +222,11 @@ struct erofs_xattr_ibody_header {
>   #define EROFS_XATTR_LONG_PREFIX		0x80
>   #define EROFS_XATTR_LONG_PREFIX_MASK	0x7f
>   
> +#define EROFS_XATTR_FILTER_BITS		32
> +#define EROFS_XATTR_FILTER_MASK		(EROFS_XATTR_FILTER_BITS - 1)

Is this useful, we could just replace it to
(EROFS_XATTR_FILTER_BITS - 1) directly.


Otherwise it looks good to me,

Thanks,
Gao Xiang
Alexander Larsson July 5, 2023, 7:43 a.m. UTC | #2 
On Wed, Jul 5, 2023 at 9:25 AM Gao Xiang <hsiangkao@linux.alibaba.com> wrote:
>
>
>
> On 2023/7/5 15:04, Jingbo Xu wrote:
> > The xattr name bloom filter feature is going to be introduced to speed
> > up the negative xattr lookup, e.g. system.posix_acl_[access|default]
> > lookup when running "ls -lR" workload.
> >
> > The number of common used extended attributes (n) is approximately 30.
>
> There are some commonly used extended attributes (n) and the total number
> of these is 31:
>
> >
> >       trusted.overlay.opaque
> >       trusted.overlay.redirect
> >       trusted.overlay.origin
> >       trusted.overlay.impure
> >       trusted.overlay.nlink
> >       trusted.overlay.upper
> >       trusted.overlay.metacopy
> >       trusted.overlay.protattr
> >       user.overlay.opaque
> >       user.overlay.redirect
> >       user.overlay.origin
> >       user.overlay.impure
> >       user.overlay.nlink
> >       user.overlay.upper
> >       user.overlay.metacopy
> >       user.overlay.protattr
> >       security.evm
> >       security.ima
> >       security.selinux
> >       security.SMACK64
> >       security.SMACK64IPIN
> >       security.SMACK64IPOUT
> >       security.SMACK64EXEC
> >       security.SMACK64TRANSMUTE
> >       security.SMACK64MMAP
> >       security.apparmor
> >       security.capability
> >       system.posix_acl_access
> >       system.posix_acl_default
> >       user.mime_type
> >
> > Given the number of bits of the bloom filter (m) is 32, the optimal
> > value for the number of the hash functions (k) is 1 (ln2 * m/n = 0.74).
> >
> > The single hash function is implemented as:
> >
> >       xxh32(name, strlen(name), EROFS_XATTR_FILTER_SEED + index)
> >
> > where index represents the index of corresponding predefined short name
>
> where `index`...
>
>
>
> > prefix, while name represents the name string after stripping the above
> > predefined name prefix.
> >
> > The constant magic number EROFS_XATTR_FILTER_SEED, i.e. 0x25BBE08F, is
> > used to give a better spread when mapping these 30 extended attributes
> > into 32-bit bloom filter as:
> >
> >       bit  0: security.ima
> >       bit  1:
> >       bit  2: trusted.overlay.nlink
> >       bit  3:
> >       bit  4: user.overlay.nlink
> >       bit  5: trusted.overlay.upper
> >       bit  6: user.overlay.origin
> >       bit  7: trusted.overlay.protattr
> >       bit  8: security.apparmor
> >       bit  9: user.overlay.protattr
> >       bit 10: user.overlay.opaque
> >       bit 11: security.selinux
> >       bit 12: security.SMACK64TRANSMUTE
> >       bit 13: security.SMACK64
> >       bit 14: security.SMACK64MMAP
> >       bit 15: user.overlay.impure
> >       bit 16: security.SMACK64IPIN
> >       bit 17: trusted.overlay.redirect
> >       bit 18: trusted.overlay.origin
> >       bit 19: security.SMACK64IPOUT
> >       bit 20: trusted.overlay.opaque
> >       bit 21: system.posix_acl_default
> >       bit 22:
> >       bit 23: user.mime_type
> >       bit 24: trusted.overlay.impure
> >       bit 25: security.SMACK64EXEC
> >       bit 26: user.overlay.redirect
> >       bit 27: user.overlay.upper
> >       bit 28: security.evm
> >       bit 29: security.capability
> >       bit 30: system.posix_acl_access
> >       bit 31: trusted.overlay.metacopy, user.overlay.metacopy
> >
> > The h_name_filter field is introduced to the on-disk per-inode xattr
> > header to place the corresponding xattr name filter, where bit value 1
> > indicates non-existence for compatibility.
> >
> > This feature is indicated by EROFS_FEATURE_COMPAT_XATTR_FILTER
> > compatible feature bit.
> >
> > Suggested-by: Alexander Larsson <alexl@redhat.com>
> > Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
> > ---
> >   fs/erofs/erofs_fs.h | 8 +++++++-
> >   1 file changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/erofs/erofs_fs.h b/fs/erofs/erofs_fs.h
> > index 2c7b16e340fe..b4b6235fd720 100644
> > --- a/fs/erofs/erofs_fs.h
> > +++ b/fs/erofs/erofs_fs.h
> > @@ -13,6 +13,7 @@
> >
> >   #define EROFS_FEATURE_COMPAT_SB_CHKSUM          0x00000001
> >   #define EROFS_FEATURE_COMPAT_MTIME              0x00000002
> > +#define EROFS_FEATURE_COMPAT_XATTR_FILTER    0x00000004
>
> I'd suggest that if we could leave one reserved byte in the
> superblock for now (and checking if it's 0) since
>    1) xattr filter feature is a compatible feature;
>    2) I'm not sure if the implementation could be changed.
>
> so that later implementation changes won't bother compat bits
> again.

I would very much like to generate these bloom filters in composefs
right now, before the composefs v1 format is completely locked down,
and this should be fully possible given that this is a backwards
compat change. But this is only possible if it doesn't require a
feature flag like this that makes old erofs versions not mount the
image.
Gao Xiang July 5, 2023, 7:51 a.m. UTC | #3 
On 2023/7/5 15:43, Alexander Larsson wrote:
> On Wed, Jul 5, 2023 at 9:25 AM Gao Xiang <hsiangkao@linux.alibaba.com> wrote:
>>
>>
>>
>> On 2023/7/5 15:04, Jingbo Xu wrote:
>>> The xattr name bloom filter feature is going to be introduced to speed
>>> up the negative xattr lookup, e.g. system.posix_acl_[access|default]
>>> lookup when running "ls -lR" workload.
>>>
>>> The number of common used extended attributes (n) is approximately 30.
>>
>> There are some commonly used extended attributes (n) and the total number
>> of these is 31:
>>
>>>
>>>        trusted.overlay.opaque
>>>        trusted.overlay.redirect
>>>        trusted.overlay.origin
>>>        trusted.overlay.impure
>>>        trusted.overlay.nlink
>>>        trusted.overlay.upper
>>>        trusted.overlay.metacopy
>>>        trusted.overlay.protattr
>>>        user.overlay.opaque
>>>        user.overlay.redirect
>>>        user.overlay.origin
>>>        user.overlay.impure
>>>        user.overlay.nlink
>>>        user.overlay.upper
>>>        user.overlay.metacopy
>>>        user.overlay.protattr
>>>        security.evm
>>>        security.ima
>>>        security.selinux
>>>        security.SMACK64
>>>        security.SMACK64IPIN
>>>        security.SMACK64IPOUT
>>>        security.SMACK64EXEC
>>>        security.SMACK64TRANSMUTE
>>>        security.SMACK64MMAP
>>>        security.apparmor
>>>        security.capability
>>>        system.posix_acl_access
>>>        system.posix_acl_default
>>>        user.mime_type
>>>
>>> Given the number of bits of the bloom filter (m) is 32, the optimal
>>> value for the number of the hash functions (k) is 1 (ln2 * m/n = 0.74).
>>>
>>> The single hash function is implemented as:
>>>
>>>        xxh32(name, strlen(name), EROFS_XATTR_FILTER_SEED + index)
>>>
>>> where index represents the index of corresponding predefined short name
>>
>> where `index`...
>>
>>
>>
>>> prefix, while name represents the name string after stripping the above
>>> predefined name prefix.
>>>
>>> The constant magic number EROFS_XATTR_FILTER_SEED, i.e. 0x25BBE08F, is
>>> used to give a better spread when mapping these 30 extended attributes
>>> into 32-bit bloom filter as:
>>>
>>>        bit  0: security.ima
>>>        bit  1:
>>>        bit  2: trusted.overlay.nlink
>>>        bit  3:
>>>        bit  4: user.overlay.nlink
>>>        bit  5: trusted.overlay.upper
>>>        bit  6: user.overlay.origin
>>>        bit  7: trusted.overlay.protattr
>>>        bit  8: security.apparmor
>>>        bit  9: user.overlay.protattr
>>>        bit 10: user.overlay.opaque
>>>        bit 11: security.selinux
>>>        bit 12: security.SMACK64TRANSMUTE
>>>        bit 13: security.SMACK64
>>>        bit 14: security.SMACK64MMAP
>>>        bit 15: user.overlay.impure
>>>        bit 16: security.SMACK64IPIN
>>>        bit 17: trusted.overlay.redirect
>>>        bit 18: trusted.overlay.origin
>>>        bit 19: security.SMACK64IPOUT
>>>        bit 20: trusted.overlay.opaque
>>>        bit 21: system.posix_acl_default
>>>        bit 22:
>>>        bit 23: user.mime_type
>>>        bit 24: trusted.overlay.impure
>>>        bit 25: security.SMACK64EXEC
>>>        bit 26: user.overlay.redirect
>>>        bit 27: user.overlay.upper
>>>        bit 28: security.evm
>>>        bit 29: security.capability
>>>        bit 30: system.posix_acl_access
>>>        bit 31: trusted.overlay.metacopy, user.overlay.metacopy
>>>
>>> The h_name_filter field is introduced to the on-disk per-inode xattr
>>> header to place the corresponding xattr name filter, where bit value 1
>>> indicates non-existence for compatibility.
>>>
>>> This feature is indicated by EROFS_FEATURE_COMPAT_XATTR_FILTER
>>> compatible feature bit.
>>>
>>> Suggested-by: Alexander Larsson <alexl@redhat.com>
>>> Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
>>> ---
>>>    fs/erofs/erofs_fs.h | 8 +++++++-
>>>    1 file changed, 7 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/fs/erofs/erofs_fs.h b/fs/erofs/erofs_fs.h
>>> index 2c7b16e340fe..b4b6235fd720 100644
>>> --- a/fs/erofs/erofs_fs.h
>>> +++ b/fs/erofs/erofs_fs.h
>>> @@ -13,6 +13,7 @@
>>>
>>>    #define EROFS_FEATURE_COMPAT_SB_CHKSUM          0x00000001
>>>    #define EROFS_FEATURE_COMPAT_MTIME              0x00000002
>>> +#define EROFS_FEATURE_COMPAT_XATTR_FILTER    0x00000004
>>
>> I'd suggest that if we could leave one reserved byte in the
>> superblock for now (and checking if it's 0) since
>>     1) xattr filter feature is a compatible feature;
>>     2) I'm not sure if the implementation could be changed.
>>
>> so that later implementation changes won't bother compat bits
>> again.
> 
> I would very much like to generate these bloom filters in composefs
> right now, before the composefs v1 format is completely locked down,
> and this should be fully possible given that this is a backwards
> compat change. But this is only possible if it doesn't require a
> feature flag like this that makes old erofs versions not mount the
> image.

EROFS has two types of feature bits:

  1) compat flags, which doesn't block mounting on old kernels;
  2) incompat flags, which will block mounting on old kernels.

here bloom filter use a new compat flag, so old kernels will just
ignore this and mount.  compat flags just indicates that "an image
with a feature, and you could use it or not".

Here I just meant the bloom filter internals are fixed for now,
so that we might reserve a byte in the on-disk super block for
later potential changes (if any).  And don't need to bother another
new compat flag.

Thanks,
Gao Xiang
Alexander Larsson July 5, 2023, 8:12 a.m. UTC | #4 
On Wed, Jul 5, 2023 at 9:51 AM Gao Xiang <hsiangkao@linux.alibaba.com> wrote:
>
>
>
> On 2023/7/5 15:43, Alexander Larsson wrote:
> > On Wed, Jul 5, 2023 at 9:25 AM Gao Xiang <hsiangkao@linux.alibaba.com> wrote:
> >>
> >>
> >>
> >> On 2023/7/5 15:04, Jingbo Xu wrote:
> >>> The xattr name bloom filter feature is going to be introduced to speed
> >>> up the negative xattr lookup, e.g. system.posix_acl_[access|default]
> >>> lookup when running "ls -lR" workload.
> >>>
> >>> The number of common used extended attributes (n) is approximately 30.
> >>
> >> There are some commonly used extended attributes (n) and the total number
> >> of these is 31:
> >>
> >>>
> >>>        trusted.overlay.opaque
> >>>        trusted.overlay.redirect
> >>>        trusted.overlay.origin
> >>>        trusted.overlay.impure
> >>>        trusted.overlay.nlink
> >>>        trusted.overlay.upper
> >>>        trusted.overlay.metacopy
> >>>        trusted.overlay.protattr
> >>>        user.overlay.opaque
> >>>        user.overlay.redirect
> >>>        user.overlay.origin
> >>>        user.overlay.impure
> >>>        user.overlay.nlink
> >>>        user.overlay.upper
> >>>        user.overlay.metacopy
> >>>        user.overlay.protattr
> >>>        security.evm
> >>>        security.ima
> >>>        security.selinux
> >>>        security.SMACK64
> >>>        security.SMACK64IPIN
> >>>        security.SMACK64IPOUT
> >>>        security.SMACK64EXEC
> >>>        security.SMACK64TRANSMUTE
> >>>        security.SMACK64MMAP
> >>>        security.apparmor
> >>>        security.capability
> >>>        system.posix_acl_access
> >>>        system.posix_acl_default
> >>>        user.mime_type
> >>>
> >>> Given the number of bits of the bloom filter (m) is 32, the optimal
> >>> value for the number of the hash functions (k) is 1 (ln2 * m/n = 0.74).
> >>>
> >>> The single hash function is implemented as:
> >>>
> >>>        xxh32(name, strlen(name), EROFS_XATTR_FILTER_SEED + index)
> >>>
> >>> where index represents the index of corresponding predefined short name
> >>
> >> where `index`...
> >>
> >>
> >>
> >>> prefix, while name represents the name string after stripping the above
> >>> predefined name prefix.
> >>>
> >>> The constant magic number EROFS_XATTR_FILTER_SEED, i.e. 0x25BBE08F, is
> >>> used to give a better spread when mapping these 30 extended attributes
> >>> into 32-bit bloom filter as:
> >>>
> >>>        bit  0: security.ima
> >>>        bit  1:
> >>>        bit  2: trusted.overlay.nlink
> >>>        bit  3:
> >>>        bit  4: user.overlay.nlink
> >>>        bit  5: trusted.overlay.upper
> >>>        bit  6: user.overlay.origin
> >>>        bit  7: trusted.overlay.protattr
> >>>        bit  8: security.apparmor
> >>>        bit  9: user.overlay.protattr
> >>>        bit 10: user.overlay.opaque
> >>>        bit 11: security.selinux
> >>>        bit 12: security.SMACK64TRANSMUTE
> >>>        bit 13: security.SMACK64
> >>>        bit 14: security.SMACK64MMAP
> >>>        bit 15: user.overlay.impure
> >>>        bit 16: security.SMACK64IPIN
> >>>        bit 17: trusted.overlay.redirect
> >>>        bit 18: trusted.overlay.origin
> >>>        bit 19: security.SMACK64IPOUT
> >>>        bit 20: trusted.overlay.opaque
> >>>        bit 21: system.posix_acl_default
> >>>        bit 22:
> >>>        bit 23: user.mime_type
> >>>        bit 24: trusted.overlay.impure
> >>>        bit 25: security.SMACK64EXEC
> >>>        bit 26: user.overlay.redirect
> >>>        bit 27: user.overlay.upper
> >>>        bit 28: security.evm
> >>>        bit 29: security.capability
> >>>        bit 30: system.posix_acl_access
> >>>        bit 31: trusted.overlay.metacopy, user.overlay.metacopy
> >>>
> >>> The h_name_filter field is introduced to the on-disk per-inode xattr
> >>> header to place the corresponding xattr name filter, where bit value 1
> >>> indicates non-existence for compatibility.
> >>>
> >>> This feature is indicated by EROFS_FEATURE_COMPAT_XATTR_FILTER
> >>> compatible feature bit.
> >>>
> >>> Suggested-by: Alexander Larsson <alexl@redhat.com>
> >>> Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
> >>> ---
> >>>    fs/erofs/erofs_fs.h | 8 +++++++-
> >>>    1 file changed, 7 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/fs/erofs/erofs_fs.h b/fs/erofs/erofs_fs.h
> >>> index 2c7b16e340fe..b4b6235fd720 100644
> >>> --- a/fs/erofs/erofs_fs.h
> >>> +++ b/fs/erofs/erofs_fs.h
> >>> @@ -13,6 +13,7 @@
> >>>
> >>>    #define EROFS_FEATURE_COMPAT_SB_CHKSUM          0x00000001
> >>>    #define EROFS_FEATURE_COMPAT_MTIME              0x00000002
> >>> +#define EROFS_FEATURE_COMPAT_XATTR_FILTER    0x00000004
> >>
> >> I'd suggest that if we could leave one reserved byte in the
> >> superblock for now (and checking if it's 0) since
> >>     1) xattr filter feature is a compatible feature;
> >>     2) I'm not sure if the implementation could be changed.
> >>
> >> so that later implementation changes won't bother compat bits
> >> again.
> >
> > I would very much like to generate these bloom filters in composefs
> > right now, before the composefs v1 format is completely locked down,
> > and this should be fully possible given that this is a backwards
> > compat change. But this is only possible if it doesn't require a
> > feature flag like this that makes old erofs versions not mount the
> > image.
>
> EROFS has two types of feature bits:
>
>   1) compat flags, which doesn't block mounting on old kernels;
>   2) incompat flags, which will block mounting on old kernels.
>
> here bloom filter use a new compat flag, so old kernels will just
> ignore this and mount.  compat flags just indicates that "an image
> with a feature, and you could use it or not".
>
> Here I just meant the bloom filter internals are fixed for now,
> so that we might reserve a byte in the on-disk super block for
> later potential changes (if any).  And don't need to bother another
> new compat flag.

Cool. Then we're all good!
Gao Xiang July 5, 2023, 8:13 a.m. UTC | #5 
On 2023/7/5 16:12, Alexander Larsson wrote:
> On Wed, Jul 5, 2023 at 9:51 AM Gao Xiang <hsiangkao@linux.alibaba.com> wrote:
>>
>>
>>
>> On 2023/7/5 15:43, Alexander Larsson wrote:
>>> On Wed, Jul 5, 2023 at 9:25 AM Gao Xiang <hsiangkao@linux.alibaba.com> wrote:
>>>>
>>>>
>>>>
>>>> On 2023/7/5 15:04, Jingbo Xu wrote:
>>>>> The xattr name bloom filter feature is going to be introduced to speed
>>>>> up the negative xattr lookup, e.g. system.posix_acl_[access|default]
>>>>> lookup when running "ls -lR" workload.
>>>>>
>>>>> The number of common used extended attributes (n) is approximately 30.
>>>>
>>>> There are some commonly used extended attributes (n) and the total number
>>>> of these is 31:
>>>>
>>>>>
>>>>>         trusted.overlay.opaque
>>>>>         trusted.overlay.redirect
>>>>>         trusted.overlay.origin
>>>>>         trusted.overlay.impure
>>>>>         trusted.overlay.nlink
>>>>>         trusted.overlay.upper
>>>>>         trusted.overlay.metacopy
>>>>>         trusted.overlay.protattr
>>>>>         user.overlay.opaque
>>>>>         user.overlay.redirect
>>>>>         user.overlay.origin
>>>>>         user.overlay.impure
>>>>>         user.overlay.nlink
>>>>>         user.overlay.upper
>>>>>         user.overlay.metacopy
>>>>>         user.overlay.protattr
>>>>>         security.evm
>>>>>         security.ima
>>>>>         security.selinux
>>>>>         security.SMACK64
>>>>>         security.SMACK64IPIN
>>>>>         security.SMACK64IPOUT
>>>>>         security.SMACK64EXEC
>>>>>         security.SMACK64TRANSMUTE
>>>>>         security.SMACK64MMAP
>>>>>         security.apparmor
>>>>>         security.capability
>>>>>         system.posix_acl_access
>>>>>         system.posix_acl_default
>>>>>         user.mime_type
>>>>>
>>>>> Given the number of bits of the bloom filter (m) is 32, the optimal
>>>>> value for the number of the hash functions (k) is 1 (ln2 * m/n = 0.74).
>>>>>
>>>>> The single hash function is implemented as:
>>>>>
>>>>>         xxh32(name, strlen(name), EROFS_XATTR_FILTER_SEED + index)
>>>>>
>>>>> where index represents the index of corresponding predefined short name
>>>>
>>>> where `index`...
>>>>
>>>>
>>>>
>>>>> prefix, while name represents the name string after stripping the above
>>>>> predefined name prefix.
>>>>>
>>>>> The constant magic number EROFS_XATTR_FILTER_SEED, i.e. 0x25BBE08F, is
>>>>> used to give a better spread when mapping these 30 extended attributes
>>>>> into 32-bit bloom filter as:
>>>>>
>>>>>         bit  0: security.ima
>>>>>         bit  1:
>>>>>         bit  2: trusted.overlay.nlink
>>>>>         bit  3:
>>>>>         bit  4: user.overlay.nlink
>>>>>         bit  5: trusted.overlay.upper
>>>>>         bit  6: user.overlay.origin
>>>>>         bit  7: trusted.overlay.protattr
>>>>>         bit  8: security.apparmor
>>>>>         bit  9: user.overlay.protattr
>>>>>         bit 10: user.overlay.opaque
>>>>>         bit 11: security.selinux
>>>>>         bit 12: security.SMACK64TRANSMUTE
>>>>>         bit 13: security.SMACK64
>>>>>         bit 14: security.SMACK64MMAP
>>>>>         bit 15: user.overlay.impure
>>>>>         bit 16: security.SMACK64IPIN
>>>>>         bit 17: trusted.overlay.redirect
>>>>>         bit 18: trusted.overlay.origin
>>>>>         bit 19: security.SMACK64IPOUT
>>>>>         bit 20: trusted.overlay.opaque
>>>>>         bit 21: system.posix_acl_default
>>>>>         bit 22:
>>>>>         bit 23: user.mime_type
>>>>>         bit 24: trusted.overlay.impure
>>>>>         bit 25: security.SMACK64EXEC
>>>>>         bit 26: user.overlay.redirect
>>>>>         bit 27: user.overlay.upper
>>>>>         bit 28: security.evm
>>>>>         bit 29: security.capability
>>>>>         bit 30: system.posix_acl_access
>>>>>         bit 31: trusted.overlay.metacopy, user.overlay.metacopy
>>>>>
>>>>> The h_name_filter field is introduced to the on-disk per-inode xattr
>>>>> header to place the corresponding xattr name filter, where bit value 1
>>>>> indicates non-existence for compatibility.
>>>>>
>>>>> This feature is indicated by EROFS_FEATURE_COMPAT_XATTR_FILTER
>>>>> compatible feature bit.
>>>>>
>>>>> Suggested-by: Alexander Larsson <alexl@redhat.com>
>>>>> Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
>>>>> ---
>>>>>     fs/erofs/erofs_fs.h | 8 +++++++-
>>>>>     1 file changed, 7 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/fs/erofs/erofs_fs.h b/fs/erofs/erofs_fs.h
>>>>> index 2c7b16e340fe..b4b6235fd720 100644
>>>>> --- a/fs/erofs/erofs_fs.h
>>>>> +++ b/fs/erofs/erofs_fs.h
>>>>> @@ -13,6 +13,7 @@
>>>>>
>>>>>     #define EROFS_FEATURE_COMPAT_SB_CHKSUM          0x00000001
>>>>>     #define EROFS_FEATURE_COMPAT_MTIME              0x00000002
>>>>> +#define EROFS_FEATURE_COMPAT_XATTR_FILTER    0x00000004
>>>>
>>>> I'd suggest that if we could leave one reserved byte in the
>>>> superblock for now (and checking if it's 0) since
>>>>      1) xattr filter feature is a compatible feature;
>>>>      2) I'm not sure if the implementation could be changed.
>>>>
>>>> so that later implementation changes won't bother compat bits
>>>> again.
>>>
>>> I would very much like to generate these bloom filters in composefs
>>> right now, before the composefs v1 format is completely locked down,
>>> and this should be fully possible given that this is a backwards
>>> compat change. But this is only possible if it doesn't require a
>>> feature flag like this that makes old erofs versions not mount the
>>> image.
>>
>> EROFS has two types of feature bits:
>>
>>    1) compat flags, which doesn't block mounting on old kernels;
>>    2) incompat flags, which will block mounting on old kernels.
>>
>> here bloom filter use a new compat flag, so old kernels will just
>> ignore this and mount.  compat flags just indicates that "an image
>> with a feature, and you could use it or not".
>>
>> Here I just meant the bloom filter internals are fixed for now,
>> so that we might reserve a byte in the on-disk super block for
>> later potential changes (if any).  And don't need to bother another
>> new compat flag.
> 
> Cool. Then we're all good!

:)

>
diff mbox series

Patch

diff --git a/fs/erofs/erofs_fs.h b/fs/erofs/erofs_fs.h
index 2c7b16e340fe..b4b6235fd720 100644
--- a/fs/erofs/erofs_fs.h
+++ b/fs/erofs/erofs_fs.h
@@ -13,6 +13,7 @@ 
 
 #define EROFS_FEATURE_COMPAT_SB_CHKSUM          0x00000001
 #define EROFS_FEATURE_COMPAT_MTIME              0x00000002
+#define EROFS_FEATURE_COMPAT_XATTR_FILTER	0x00000004
 
 /*
  * Any bits that aren't in EROFS_ALL_FEATURE_INCOMPAT should
@@ -200,7 +201,7 @@  struct erofs_inode_extended {
  * for read-only fs, no need to introduce h_refcount
  */
 struct erofs_xattr_ibody_header {
-	__le32 h_reserved;
+	__le32 h_name_filter;		/* bit value 1 indicates not-present */
 	__u8   h_shared_count;
 	__u8   h_reserved2[7];
 	__le32 h_shared_xattrs[];       /* shared xattr id array */
@@ -221,6 +222,11 @@  struct erofs_xattr_ibody_header {
 #define EROFS_XATTR_LONG_PREFIX		0x80
 #define EROFS_XATTR_LONG_PREFIX_MASK	0x7f
 
+#define EROFS_XATTR_FILTER_BITS		32
+#define EROFS_XATTR_FILTER_MASK		(EROFS_XATTR_FILTER_BITS - 1)
+#define EROFS_XATTR_FILTER_DEFAULT	UINT32_MAX
+#define EROFS_XATTR_FILTER_SEED		0x25BBE08F
+
 /* xattr entry (for both inline & shared xattrs) */
 struct erofs_xattr_entry {
 	__u8   e_name_len;      /* length of name */