iomap: Add done_before argument to iomap_dio_rw

Add a done_before argument to iomap_dio_rw that indicates how much of
the request has already been transferred.  When the request succeeds, we
report that done_before additional bytes were tranferred.  This is
useful for finishing a request asynchronously when part of the request
has already been completed synchronously.

We'll use that to allow iomap_dio_rw to be used with page faults
disabled: when a page fault occurs while submitting a request, we
synchronously complete the part of the request that has already been
submitted.  The caller can then take care of the page fault and call
iomap_dio_rw again for the rest of the request, passing in the number of
bytes already tranferred.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

1 files changed, 3 insertions, 2 deletions

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index f37211d3bb69..9d41b28c67ba 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1957,7 +1957,7 @@ relock:
 	}
 
 	dio = __iomap_dio_rw(iocb, from, &btrfs_dio_iomap_ops, &btrfs_dio_ops,
-			     0);
+			     0, 0);
 
 	btrfs_inode_unlock(inode, ilock_flags);
 
@@ -3658,7 +3658,8 @@ static ssize_t btrfs_direct_read(struct kiocb *iocb, struct iov_iter *to)
 		return 0;
 
 	btrfs_inode_lock(inode, BTRFS_ILOCK_SHARED);
-	ret = iomap_dio_rw(iocb, to, &btrfs_dio_iomap_ops, &btrfs_dio_ops, 0);
+	ret = iomap_dio_rw(iocb, to, &btrfs_dio_iomap_ops, &btrfs_dio_ops,
+			   0, 0);
 	btrfs_inode_unlock(inode, BTRFS_ILOCK_SHARED);
 	return ret;
 }