Re: [PATCH 09/27] xfs: split xfs_itruncate_finish

Dave Chinner
2011-06-30T02:44:33Z

On Wed, Jun 29, 2011 at 10:01:18AM -0400, Christoph Hellwig wrote:
> Split the guts of xfs_itruncate_finish that loop over the existing extents
> and calls xfs_bunmapi on them into a new helper, xfs_itruncate_externs.
> Make xfs_attr_inactive call it directly instead of xfs_itruncate_finish,
> which allows to simplify the latter a lot, by only letting it deal with
> the data fork. As a result xfs_itruncate_finish is renamed to
> xfs_itruncate_data to make its use case more obvious.
>
> Also remove the sync parameter from xfs_itruncate_data, which has been
> unessecary since the introduction of the busy extent list in 2002, and
> completely dead code since 2003 when the XFS_BMAPI_ASYNC parameter was
> made a no-op.
>
> I can't actually see why the xfs_attr_inactive needs to set the transaction
> sync, but let's keep this patch simple and without changes in behaviour.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Overall, looks good. A few minor comments in line, but consider it

Reviewed-by: Dave Chinner <dchinner@redhat.com>

> + struct xfs_mount *mp = ip->i_mount;
> + struct xfs_trans *ntp = *tpp;
> + xfs_bmap_free_t free_list;
> + xfs_fsblock_t first_block;
> + xfs_fileoff_t first_unmap_block;
> + xfs_fileoff_t last_block;
> + xfs_filblks_t unmap_len;
> + int committed;
> + int error = 0;
> + int done = 0;
>
> ASSERT(xfs_isilocked(ip, XFS_ILOCK_EXCL|XFS_IOLOCK_EXCL));
> - ASSERT((new_size == 0) || (new_size <= ip->i_size));
> - ASSERT(*tp != NULL);
> - ASSERT((*tp)->t_flags & XFS_TRANS_PERM_LOG_RES);
> - ASSERT(ip->i_transp == *tp);
> + ASSERT(new_size == 0 || new_size <= ip->i_size);

If new_size == 0, then it will always be <= ip->i_size, so that's
kind of a redundant check. I think this really should be two
different asserts, one that validates the data fork new_size range,
and one that validates the attr fork truncate to zero length only
condition:

ASSERT(new_size <= ip->i_size);
ASSERT(whichfork != XFS_ATTR_FORK || new_size == 0);

> @@ -1464,15 +1311,16 @@ xfs_itruncate_finish(
> }
>
> ntp = xfs_trans_dup(ntp);
> - error = xfs_trans_commit(*tp, 0);
> - *tp = ntp;
> + error = xfs_trans_commit(*tpp, 0);
> + *tpp = ntp;

I've always found this a mess to follow which transaction is which
because of the rewriting of ntp. This is easier to follow:

ntp = xfs_trans_dup(*tpp);
error = xfs_trans_commit(*tpp, 0);
*tpp = ntp;

Now it's clear that we are duplicating *tpp, then committing it, and
then setting it to the duplicated transaction. Now I don't have to
go look at all the surrounding code to remind myself what ntp
contains to validate that the fragment of code is doing the right
thing.....

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com