Re: [RFC PATCH 2/2] xfs_export_operations.commit_metadata

Christoph Hellwig
2010-02-10T09:07:51Z

On Tue, Feb 09, 2010 at 06:33:37PM -0600, Ben Myers wrote:
> Here is the commit_metadata export_operation for xfs. We take two dentries and
> force the log up to the larger lsn. It looks to me that in nfsd the child is
> always modified after the parent so generally we expect the child's lsn to be
> larger. If that's not the case we'll just force the entire thing.
>
> The basic form of this is based upon one of Christoph's suggestions. I'm an
> xfs newbie so I'm not very comfortable with it yet. My understanding is that I
> need to verify that all of the necessary changes make it into the transations
> we're forcing into the log here. I am still looking into that and hopefully
> the XFS gurus can continue to provide guidance.

Ccing the xfs list would help with that :) Anyway, I think it looks
pretty good, but there's quite a few smaller nitpicks:

> +STATIC int
> +xfs_fs_nfs_commit_metadata(
> + struct dentry *parent,
> + struct dentry *child)
> +{
> + struct xfs_inode *p_xip = NULL, *c_xip = NULL;

Normal xfs naming would be dp for the parent, and ip for the child,
it would be good to stick to that.

> + struct xfs_mount *i_mount = NULL;

Normal name all over xfs would be mp.

> + } else if (parent && child) {
> + p_xip = XFS_I(parent->d_inode);
> + c_xip = XFS_I(child->d_inode);
> + xfs_ilock(p_xip, XFS_ILOCK_SHARED);
> + xfs_ilock(c_xip, XFS_ILOCK_SHARED);

If we need to lock both parent and child we need to use
xfs_lock_two_inodes to make sure the lock order is correct.

> + if (xfs_ipincount(c_xip)) {
> + /*
> + * AFAICS the child is always modified after the parent
> + * in nfsd so should always have a larger lsn.
> + */
> + if (c_xip->i_itemp->ili_last_lsn > force_lsn) {
> + force_lsn = c_xip->i_itemp->ili_last_lsn;
> + } else {
> + force_lsn = 0; /* whole thing */
> + }

I wouldn't rely on that and always take the larger one.

Now with the simplification of always having a non-zero first argument
suggested in the previous mail this might be simplified down to:

STATIC int
xfs_fs_nfs_commit_metadata(
struct dentry *parent,
struct dentry *child)
{
struct xfs_inode *dp = XFS_I(parent->d_inode);
struct xfs_inode *ip = NULL;
struct xfs_mount *mp = dp->i_mount;
xfs_lsn_t force_lsn = 0;
int error = 0;

if (child) {
ip = XFS_I(child->d_inode);
xfs_lock_two_inodes(dp, ip, XFS_ILOCK_SHARED);
} else {
xfs_ilock(dp, XFS_ILOCK_SHARED);
}

if (xfs_ipincount(dp))
force_lsn = dp->i_itemp->ili_last_lsn;
if (ip && xfs_ipincount(ip))
force_lsn = max(force_lsn, ip->i_itemp->ili_last_lsn);

error = _xfs_log_force_lsn(mp, force_lsn, NULL);

if (ip)
xfs_iunlock(ip, XFS_ILOCK_SHARED);
xfs_iunlock(dp, XFS_ILOCK_SHARED);

return error;
}

Note that _xfs_log_force_lsn is new in the XFS tree, mainline still
has _xfs_log_force with an lsn argument.

Also note that ->commit_metadata probably should take just two inodes
instead of two dentires given the level it operates on, but it shouldn't
matter too much.