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

["J. Bruce Fields" <bfields@fieldses.org>]

On Tue, Jan 24, 2017 at 09:06:04AM -0500, Jeff Layton wrote:
> 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>

OK, applying.--b.