[v7,7/9] nfsd: use the getattr operation to fetch i_version

  Now that we can call into vfs_getattr to get the i_version field, use
that facility to fetch it instead of doing it in nfsd4_change_attribute.

Neil also pointed out recently that IS_I_VERSION directory operations
are always logged, and so we only need to mitigate the rollback problem
on regular files. Also, we don't need to factor in the ctime when
reexporting NFS or Ceph.

Set the STATX_VERSION (and BTIME) bits in the request when we're dealing
with a v4 request. Then, instead of looking at IS_I_VERSION when
generating the change attr, look at the result mask and only use it if
STATX_VERSION is set.

Change nfsd4_change_attribute to only factor in the ctime if it's a regular
file and the fs doesn't advertise STATX_ATTR_VERSION_MONOTONIC.

Reviewed-by: NeilBrown <neilb@suse.de>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 fs/nfsd/nfs4xdr.c |  4 +++-
 fs/nfsd/nfsfh.c   | 53 +++++++++++++++++++++++++++++++----------------
 fs/nfsd/vfs.h     |  7 ++++++-
 3 files changed, 44 insertions(+), 20 deletions(-)
  

> On Oct 17, 2022, at 6:57 AM, Jeff Layton <jlayton@kernel.org> wrote:
> 
> Now that we can call into vfs_getattr to get the i_version field, use
> that facility to fetch it instead of doing it in nfsd4_change_attribute.
> 
> Neil also pointed out recently that IS_I_VERSION directory operations
> are always logged, and so we only need to mitigate the rollback problem
> on regular files. Also, we don't need to factor in the ctime when
> reexporting NFS or Ceph.
> 
> Set the STATX_VERSION (and BTIME) bits in the request when we're dealing
> with a v4 request. Then, instead of looking at IS_I_VERSION when
> generating the change attr, look at the result mask and only use it if
> STATX_VERSION is set.
> 
> Change nfsd4_change_attribute to only factor in the ctime if it's a regular
> file and the fs doesn't advertise STATX_ATTR_VERSION_MONOTONIC.
> 
> Reviewed-by: NeilBrown <neilb@suse.de>
> Signed-off-by: Jeff Layton <jlayton@kernel.org>

Acked-by: Chuck Lever <chuck.lever@oracle.com>


> ---
> fs/nfsd/nfs4xdr.c |  4 +++-
> fs/nfsd/nfsfh.c   | 53 +++++++++++++++++++++++++++++++----------------
> fs/nfsd/vfs.h     |  7 ++++++-
> 3 files changed, 44 insertions(+), 20 deletions(-)
> 
> diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
> index bcfeb1a922c0..c19b6b00b620 100644
> --- a/fs/nfsd/nfs4xdr.c
> +++ b/fs/nfsd/nfs4xdr.c
> @@ -2906,7 +2906,9 @@ nfsd4_encode_fattr(struct xdr_stream *xdr, struct svc_fh *fhp,
> 			goto out;
> 	}
> 
> -	err = vfs_getattr(&path, &stat, STATX_BASIC_STATS, AT_STATX_SYNC_AS_STAT);
> +	err = vfs_getattr(&path, &stat,
> +			  STATX_BASIC_STATS | STATX_BTIME | STATX_VERSION,
> +			  AT_STATX_SYNC_AS_STAT);
> 	if (err)
> 		goto out_nfserr;
> 	if (!(stat.result_mask & STATX_BTIME))
> diff --git a/fs/nfsd/nfsfh.c b/fs/nfsd/nfsfh.c
> index 7030d9209903..21b64ac97a06 100644
> --- a/fs/nfsd/nfsfh.c
> +++ b/fs/nfsd/nfsfh.c
> @@ -628,6 +628,10 @@ void fh_fill_pre_attrs(struct svc_fh *fhp)
> 		stat.mtime = inode->i_mtime;
> 		stat.ctime = inode->i_ctime;
> 		stat.size  = inode->i_size;
> +		if (v4 && IS_I_VERSION(inode)) {
> +			stat.version = inode_query_iversion(inode);
> +			stat.result_mask |= STATX_VERSION;
> +		}
> 	}
> 	if (v4)
> 		fhp->fh_pre_change = nfsd4_change_attribute(&stat, inode);
> @@ -659,6 +663,10 @@ void fh_fill_post_attrs(struct svc_fh *fhp)
> 	if (err) {
> 		fhp->fh_post_saved = false;
> 		fhp->fh_post_attr.ctime = inode->i_ctime;
> +		if (v4 && IS_I_VERSION(inode)) {
> +			fhp->fh_post_attr.version = inode_query_iversion(inode);
> +			fhp->fh_post_attr.result_mask |= STATX_VERSION;
> +		}
> 	} else
> 		fhp->fh_post_saved = true;
> 	if (v4)
> @@ -750,28 +758,37 @@ enum fsid_source fsid_source(const struct svc_fh *fhp)
> }
> 
> /*
> - * We could use i_version alone as the change attribute.  However,
> - * i_version can go backwards after a reboot.  On its own that doesn't
> - * necessarily cause a problem, but if i_version goes backwards and then
> - * is incremented again it could reuse a value that was previously used
> - * before boot, and a client who queried the two values might
> - * incorrectly assume nothing changed.
> + * We could use i_version alone as the change attribute.  However, i_version
> + * can go backwards on a regular file after an unclean shutdown.  On its own
> + * that doesn't necessarily cause a problem, but if i_version goes backwards
> + * and then is incremented again it could reuse a value that was previously
> + * used before boot, and a client who queried the two values might incorrectly
> + * assume nothing changed.
> + *
> + * By using both ctime and the i_version counter we guarantee that as long as
> + * time doesn't go backwards we never reuse an old value. If the filesystem
> + * advertises STATX_ATTR_VERSION_MONOTONIC, then this mitigation is not needed.
>  *
> - * By using both ctime and the i_version counter we guarantee that as
> - * long as time doesn't go backwards we never reuse an old value.
> + * We only need to do this for regular files as well. For directories, we
> + * assume that the new change attr is always logged to stable storage in some
> + * fashion before the results can be seen.
>  */
> u64 nfsd4_change_attribute(struct kstat *stat, struct inode *inode)
> {
> +	u64 chattr;
> +
> 	if (inode->i_sb->s_export_op->fetch_iversion)
> 		return inode->i_sb->s_export_op->fetch_iversion(inode);
> -	else if (IS_I_VERSION(inode)) {
> -		u64 chattr;
> -
> -		chattr =  stat->ctime.tv_sec;
> -		chattr <<= 30;
> -		chattr += stat->ctime.tv_nsec;
> -		chattr += inode_query_iversion(inode);
> -		return chattr;
> -	} else
> -		return time_to_chattr(&stat->ctime);
> +	if (stat->result_mask & STATX_VERSION) {
> +		chattr = stat->version;
> +
> +		if (S_ISREG(inode->i_mode) &&
> +		    !(stat->attributes & STATX_ATTR_VERSION_MONOTONIC)) {
> +			chattr += (u64)stat->ctime.tv_sec << 30;
> +			chattr += stat->ctime.tv_nsec;
> +		}
> +	} else {
> +		chattr = time_to_chattr(&stat->ctime);
> +	}
> +	return chattr;
> }
> diff --git a/fs/nfsd/vfs.h b/fs/nfsd/vfs.h
> index 120521bc7b24..c98e13ec37b2 100644
> --- a/fs/nfsd/vfs.h
> +++ b/fs/nfsd/vfs.h
> @@ -168,9 +168,14 @@ static inline void fh_drop_write(struct svc_fh *fh)
> 
> static inline __be32 fh_getattr(const struct svc_fh *fh, struct kstat *stat)
> {
> +	u32 request_mask = STATX_BASIC_STATS;
> 	struct path p = {.mnt = fh->fh_export->ex_path.mnt,
> 			 .dentry = fh->fh_dentry};
> -	return nfserrno(vfs_getattr(&p, stat, STATX_BASIC_STATS,
> +
> +	if (fh->fh_maxsize == NFS4_FHSIZE)
> +		request_mask |= (STATX_BTIME | STATX_VERSION);
> +
> +	return nfserrno(vfs_getattr(&p, stat, request_mask,
> 				    AT_STATX_SYNC_AS_STAT));
> }
> 
> -- 
> 2.37.3
> 

--
Chuck Lever