On Sun, Oct 8, 2017 at 8:45 PM, Dave Chinner [off-list ref] wrote:

On Fri, Oct 06, 2017 at 03:36:06PM -0700, Dan Williams wrote:

quoted

A 'lease_direct' lease requires that the vma have a valid MAP_DIRECT
mapping established. For xfs we establish a new lease and then check if
the MAP_DIRECT mapping has been broken. We want to be sure that the
process will receive notification that the MAP_DIRECT mapping is being
torn down so it knows why other code paths are throwing failures.

For example in the RDMA/ibverbs case we want ibv_reg_mr() to fail if the
MAP_DIRECT mapping is invalid or in the process of being invalidated.

Cc: Jan Kara <jack@suse.cz>
Cc: Jeff Moyer <redacted>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dave Chinner <david@fromorbit.com>
Cc: "Darrick J. Wong" <redacted>
Cc: Ross Zwisler <redacted>
Cc: Jeff Layton <redacted>
Cc: "J. Bruce Fields" <redacted>
Signed-off-by: Dan Williams <redacted>
---
 fs/xfs/xfs_file.c |   28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index e35518600e28..823b65f17429 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c

@@ -1166,6 +1166,33 @@ xfs_filemap_direct_close(
      put_map_direct_vma(vma->vm_private_data);
 }

+static struct lease_direct *
+xfs_filemap_direct_lease(
+     struct vm_area_struct   *vma,
+     void                    (*break_fn)(void *),
+     void                    *owner)
+{
+     struct lease_direct     *ld;
+
+     ld = map_direct_lease(vma, break_fn, owner);
+
+     if (IS_ERR(ld))
+             return ld;
+
+     /*
+      * We now have an established lease while the base MAP_DIRECT
+      * lease was not broken. So, we know that the "lease holder" will
+      * receive a SIGIO notification when the lease is broken and
+      * take any necessary cleanup actions.
+      */
+     if (!is_map_direct_broken(vma->vm_private_data))
+             return ld;
+
+     map_direct_lease_destroy(ld);
+
+     return ERR_PTR(-ENXIO);

What's any of this got to do with XFS? Shouldn't it be in generic
code, and called generic_filemap_direct_lease()?

True, I can move this to generic code. The filesystem is in charge of
where it wants to store the 'struct map_direct_state' context, but for
generic_filemap_direct_lease() it can just assume that it is stored in
->vm_private_data. I'll add comments to this effect on the new
routine.