On Fri, Aug 4, 2017 at 1:53 PM, Darrick J. Wong [off-list ref] wrote:

On Fri, Aug 04, 2017 at 01:47:32PM -0700, Dan Williams wrote:

quoted

On Fri, Aug 4, 2017 at 1:14 PM, Darrick J. Wong [off-list ref] wrote:

quoted

On Thu, Aug 03, 2017 at 07:28:35PM -0700, Dan Williams wrote:

quoted

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 <redacted>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Ross Zwisler <redacted>
Suggested-by: Dave Chinner <david@fromorbit.com>
Suggested-by: "Darrick J. Wong" <redacted>
Signed-off-by: Dan Williams <redacted>
---
 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...

quoted

+     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. :)

Ah, got it, thanks.