Re: [PATCH v2] nfsd: special case truncates some more

[Jeff Layton <jlayton@redhat.com>]

On Tue, 2017-01-24 at 09:22 +0100, Christoph Hellwig wrote:
> Both the NFS protocols and the Linux VFS use a setattr operation with a
> bitmap of attributs to set to set various file attributes including the
> file size and the uid/gid.
> 
> The Linux syscalls never mixe size updates with unrelated updates like
> the uid/gid, and some file systems like XFS and GFS2 rely on the fact
> that truncates might not update random other attributes, and many
> other file systems handle the case but do not update the different
> attributes in the same transaction.  NFSD on the other hand passes
> the attributes it gets on the wire more or less directly through to
> the VFS, leading to updates the file systems don't expect.  XFS at
> least has an assert on the allowed attributes, which cought an NFS
> client sets the size and group at the same time.
> 
> To handles this issue properly this switches nfsd to call vfs_truncate
> for size changes, and then handling all other attributes through
> notify_change.  As a side effect this also means less boilerplace
> code around the size change as we can now reuse the VFS code.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> 
> Changes since V1:
>  - avoid an extra setattr just for a MTIME attribute on the wire
> 
>  fs/nfsd/vfs.c | 97 +++++++++++++++++++++++------------------------------------
>  1 file changed, 37 insertions(+), 60 deletions(-)
> 
> diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
> index 26c6fdb..e91107a 100644
> --- a/fs/nfsd/vfs.c
> +++ b/fs/nfsd/vfs.c
> @@ -332,37 +332,6 @@ nfsd_sanitize_attrs(struct inode *inode, struct iattr *iap)
>  	}
>  }
>  
> -static __be32
> -nfsd_get_write_access(struct svc_rqst *rqstp, struct svc_fh *fhp,
> -		struct iattr *iap)
> -{
> -	struct inode *inode = d_inode(fhp->fh_dentry);
> -	int host_err;
> -
> -	if (iap->ia_size < inode->i_size) {
> -		__be32 err;
> -
> -		err = nfsd_permission(rqstp, fhp->fh_export, fhp->fh_dentry,
> -				NFSD_MAY_TRUNC | NFSD_MAY_OWNER_OVERRIDE);
> -		if (err)
> -			return err;
> -	}
> -
> -	host_err = get_write_access(inode);
> -	if (host_err)
> -		goto out_nfserrno;
> -
> -	host_err = locks_verify_truncate(inode, NULL, iap->ia_size);
> -	if (host_err)
> -		goto out_put_write_access;
> -	return 0;
> -
> -out_put_write_access:
> -	put_write_access(inode);
> -out_nfserrno:
> -	return nfserrno(host_err);
> -}
> -
>  /*
>   * Set various file attributes.  After this call fhp needs an fh_put.
>   */
> @@ -377,7 +346,6 @@ nfsd_setattr(struct svc_rqst *rqstp, struct svc_fh *fhp, struct iattr *iap,
>  	__be32		err;
>  	int		host_err;
>  	bool		get_write_count;
> -	int		size_change = 0;
>  
>  	if (iap->ia_valid & (ATTR_ATIME | ATTR_MTIME | ATTR_SIZE))
>  		accmode |= NFSD_MAY_WRITE|NFSD_MAY_OWNER_OVERRIDE;
> @@ -390,11 +358,11 @@ nfsd_setattr(struct svc_rqst *rqstp, struct svc_fh *fhp, struct iattr *iap,
>  	/* Get inode */
>  	err = fh_verify(rqstp, fhp, ftype, accmode);
>  	if (err)
> -		goto out;
> +		return err;
>  	if (get_write_count) {
>  		host_err = fh_want_write(fhp);
>  		if (host_err)
> -			return nfserrno(host_err);
> +			goto out_host_err;
>  	}
>  
>  	dentry = fhp->fh_dentry;
> @@ -405,50 +373,59 @@ nfsd_setattr(struct svc_rqst *rqstp, struct svc_fh *fhp, struct iattr *iap,
>  		iap->ia_valid &= ~ATTR_MODE;
>  
>  	if (!iap->ia_valid)
> -		goto out;
> +		return 0;
>  
>  	nfsd_sanitize_attrs(inode, iap);
>  
> +	if (check_guard && guardtime != inode->i_ctime.tv_sec)
> +		return nfserr_notsync;
> +
>  	/*
>  	 * The size case is special, it changes the file in addition to the
> -	 * attributes.
> +	 * attributes, and file systems don't expect it to be mixed with
> +	 * "random" attribute changes.  We thus split out the size change
> +	 * into a separate calo for vfs_truncate, and do the rest as a
> +	 * a separate setattr call.
>  	 */
>  	if (iap->ia_valid & ATTR_SIZE) {
> -		err = nfsd_get_write_access(rqstp, fhp, iap);
> -		if (err)
> -			goto out;
> -		size_change = 1;
> +		struct path path = {
> +			.mnt	= fhp->fh_export->ex_path.mnt,
> +			.dentry	= dentry,
> +		};
> +		bool implicit_mtime = false;
>  
>  		/*
> -		 * RFC5661, Section 18.30.4:
> -		 *   Changing the size of a file with SETATTR indirectly
> -		 *   changes the time_modify and change attributes.
> -		 *
> -		 * (and similar for the older RFCs)
> +		 * vfs_truncate implicity updates the mtime IFF the file size
> +		 * actually changes.  Avoid the additional seattr call below if
> +		 * the only other attribute that the client sends is the mtime.
>  		 */
> -		if (iap->ia_size != i_size_read(inode))
> -			iap->ia_valid |= ATTR_MTIME;
> -	}
> +		if (iap->ia_size != i_size_read(inode) &&
> +		    ((iap->ia_valid & ~(ATTR_SIZE | ATTR_MTIME)) == 0))
> +			implicit_mtime = true;
>  
> -	iap->ia_valid |= ATTR_CTIME;
> +		host_err = vfs_truncate(&path, iap->ia_size);
> +		if (host_err)
> +			goto out_host_err;
>  
> -	if (check_guard && guardtime != inode->i_ctime.tv_sec) {
> -		err = nfserr_notsync;
> -		goto out_put_write_access;
> +		iap->ia_valid &= ~ATTR_SIZE;
> +		if (implicit_mtime)
> +			iap->ia_valid &= ~ATTR_MTIME;
> +		if (!iap->ia_valid)
> +			goto done;
>  	}
>  
> +	iap->ia_valid |= ATTR_CTIME;
> +
>  	fh_lock(fhp);
>  	host_err = notify_change(dentry, iap, NULL);
>  	fh_unlock(fhp);
> -	err = nfserrno(host_err);
> +	if (host_err)
> +		goto out_host_err;
>  
> -out_put_write_access:
> -	if (size_change)
> -		put_write_access(inode);
> -	if (!err)
> -		err = nfserrno(commit_metadata(fhp));
> -out:
> -	return err;
> +done:
> +	host_err = commit_metadata(fhp);
> +out_host_err:
> +	return nfserrno(host_err);
>  }
>  
>  #if defined(CONFIG_NFSD_V4)

Reviewed-by: Jeff Layton <jlayton@redhat.com>