On Mon, 2017-01-23 at 16:36 +0100, Christoph Hellwig wrote:
> On Mon, Jan 23, 2017 at 01:33:48PM +0100, Christoph Hellwig wrote:
> > I'll need to look at the exact NFS semantics in that area, but after
> > a bit of research I can probably come up with something that will work.
>
> Here is my first attempt. As vfs_truncate will add the ctime and mtime
> updates when needed it just leaves handling that quirk to vfs_truncate
> and then exits early if no other attributes are set.
>
> Unfortunately at least the Linux client always seems to also request
> a mtime update with a size update. We could keep the
>
> if (iap->ia_size != i_size_read(inode))
>
> check from the old code and remove ATTR_MTIME, but these racy checks
> outside i_rwsem make me feel a bit uneasy. Jeff, Bruce - any opinion
> if we should add something like this:
>
Ok, that's more complicated than it looked at first blush. :)
To be clear, the client is requesting to set the mtime to current server
time and not to a specific mtime, right?
> /* vfs_truncate will update ctime and mtime if the size changes */
> if (iap->ia_size != i_size_read(inode))
> iap->ia_valid &= ATTR_MTIME;
>
> back to nfsd_setattr? This would avoid the additional setattr call,
> but make me feel dirty :)
>
I agree that I wouldn't want to go with a potentially racy check.
I don't see where vfs_truncate will handle the times though. do_truncate
will, but you have to pass in a non-zero time_attrs and vfs_truncate
always sets that to 0.
If we did want to do this, it seems like it might be better to just add
a new time_attrs arg to vfs_truncate that gets passed to do_truncate.
Most callers would set it to zero, but nfsd could set it to:
iap->ia_valid & (ATTR_MTIME|ATTR_CTIME)
Would that work?
> ---
> From 0e06e2fc6157bb97692ed47c21e36120efb9f15c Mon Sep 17 00:00:00 2001
> From: Christoph Hellwig <hch@xxxxxx>
> Date: Sun, 22 Jan 2017 17:17:48 +0100
> Subject: nfsd: special case truncates some more
> MIME-Version: 1.0
> Content-Type: text/plain; charset=UTF-8
> Content-Transfer-Encoding: 8bit
>
> 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 ІD 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@xxxxxx>
> ---
> fs/nfsd/vfs.c | 92 +++++++++++++++++++----------------------------------------
> 1 file changed, 30 insertions(+), 62 deletions(-)
>
> diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
> index 26c6fdb..4ca5b92 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 +373,50 @@ 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.
> + *
> + * Note that vfs_truncate will also update ctime and mtime if
> + * the file size changes.
> */
> 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,
> + };
>
> - /*
> - * 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)
> - */
> - if (iap->ia_size != i_size_read(inode))
> - iap->ia_valid |= ATTR_MTIME;
> + host_err = vfs_truncate(&path, iap->ia_size);
> + if (host_err)
> + goto out_host_err;
> +
> + iap->ia_valid &= ~ATTR_SIZE;
> + if (!iap->ia_valid)
> + goto done;
> }
>
> iap->ia_valid |= ATTR_CTIME;
>
> - if (check_guard && guardtime != inode->i_ctime.tv_sec) {
> - err = nfserr_notsync;
> - goto out_put_write_access;
> - }
> -
> 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)
--
Jeff Layton <jlayton@xxxxxxxxxxxxxxx>
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