Re: [PATCH v2 5/5] xfs: toggle XFS_DIFLAG2_IOMAP_IMMUTABLE in response to fallocate

Darrick J. Wong
2017-08-04T20:51:34Z

On Fri, Aug 04, 2017 at 01:47:32PM -0700, Dan Williams wrote:
> On Fri, Aug 4, 2017 at 1:14 PM, Darrick J. Wong <darrick.wong@oracle.com> wrote:
> > On Thu, Aug 03, 2017 at 07:28:35PM -0700, Dan Williams wrote:
> >> After validating the state of the file as not having holes, shared
> >> extents, or active mappings try to commit the
> >> XFS_DIFLAG2_IOMAP_IMMUTABLE flag to the on-disk inode metadata. If that
> >> succeeds then allow the S_IOMAP_IMMUTABLE to be set on the vfs inode.
> >>
> >> Cc: Jan Kara <jack@suse.cz>
> >> Cc: Jeff Moyer <jmoyer@redhat.com>
> >> Cc: Christoph Hellwig <hch@lst.de>
> >> Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
> >> Suggested-by: Dave Chinner <david@fromorbit.com>
> >> Suggested-by: "Darrick J. Wong" <darrick.wong@oracle.com>
> >> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> >> ---
> >> fs/xfs/xfs_bmap_util.c | 32 ++++++++++++++++++++++++++++++++
> >> 1 file changed, 32 insertions(+)
> >>
> >> diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
> >> index 70ac2d33ab27..8464c25a2403 100644
> >> --- a/fs/xfs/xfs_bmap_util.c
> >> +++ b/fs/xfs/xfs_bmap_util.c
> >> @@ -1436,9 +1436,11 @@ xfs_seal_file_space(
> >> xfs_off_t offset,
> >> xfs_off_t len)
> >> {
> >> + struct xfs_mount *mp = ip->i_mount;
> >> struct inode *inode = VFS_I(ip);
> >> struct address_space *mapping = inode->i_mapping;
> >> int error;
> >> + struct xfs_trans *tp;
> >>
> >> ASSERT(xfs_isilocked(ip, XFS_MMAPLOCK_EXCL));
> >>
> >> @@ -1454,6 +1456,10 @@ xfs_seal_file_space(
> >> if (error)
> >> return error;
> >>
> >> + error = xfs_trans_alloc(mp, &M_RES(mp)->tr_ichange, 0, 0, 0, &tp);
> >> + if (error)
> >> + return error;
> >> +
> >> xfs_ilock(ip, XFS_ILOCK_EXCL);
> >> /*
> >> * Either the size changed after we performed allocation /
> >> @@ -1486,10 +1492,20 @@ xfs_seal_file_space(
> >> if (error < 0)
> >> goto out_unlock;
> >>
> >> + xfs_trans_ijoin(tp, ip, 0);
> >
> > FWIW if you change that third parameter to XFS_ILOCK_EXCL then
> > xfs_trans_commit will do the xfs_iunlock(ip, XFS_ILOCK_EXCL) for you if
> > the commit succeeds...
> >
> >> + ip->i_d.di_flags2 |= XFS_DIFLAG2_IOMAP_IMMUTABLE;
> >> + xfs_trans_log_inode(tp, ip, XFS_ILOG_CORE);
> >> + error = xfs_trans_commit(tp);
> >> + tp = NULL; /* nothing to cancel */
> >> + if (error)
> >> + goto out_unlock;
> >> +
> >> inode->i_flags |= S_IOMAP_IMMUTABLE;
> >
> > ...and then you can just return out here.
>
> Do we not need to hold XFS_ILOCK_EXCL over ->i_flags changes, or is
> XFS_IOLOCK_EXCL enough?

Oh, heh, I missed a piece. Set the flag before the transaction commit,
because if the commit fails the fs is shut down anyway. :)

--D

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