xfs: stop using generic_file_read_iter for direct I/O

XFS already implement it's own flushing of the pagecache because it
implements proper synchronization for direct I/O reads.  This means
calling generic_file_read_iter for direct I/O is rather useless,
as it doesn't do much but updating the atime and iocb position for
us.  This also gets rid of the buffered I/O fallback that isn't used
for XFS.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

1 files changed, 13 insertions, 2 deletions

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index fdb123ffd616..440bb8b5c64d 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -289,12 +289,17 @@ xfs_file_dio_aio_read(
         struct address_space    *mapping = iocb->ki_filp->f_mapping;
         struct inode            *inode = mapping->host;
         struct xfs_inode        *ip = XFS_I(inode);
+        loff_t                  isize = i_size_read(inode);
         size_t                  count = iov_iter_count(to);
+        struct iov_iter         data;
         struct xfs_buftarg      *target;
         ssize_t                 ret = 0;
 
         trace_xfs_file_direct_read(ip, count, iocb->ki_pos);
 
+        if (!count)
+                return 0; /* skip atime */
+
         if (XFS_IS_REALTIME_INODE(ip))
                 target = ip->i_mount->m_rtdev_targp;
         else
@@ -303,7 +308,7 @@ xfs_file_dio_aio_read(
         if (!IS_DAX(inode)) {
                 /* DIO must be aligned to device logical sector size */
                 if ((iocb->ki_pos | count) & target->bt_logical_sectormask) {
-                        if (iocb->ki_pos == i_size_read(inode))
+                        if (iocb->ki_pos == isize)
                                 return 0;
                         return -EINVAL;
                 }
@@ -354,9 +359,15 @@ xfs_file_dio_aio_read(
                 xfs_rw_ilock_demote(ip, XFS_IOLOCK_EXCL);
         }
 
-        ret = generic_file_read_iter(iocb, to);
+        data = *to;
+        ret = mapping->a_ops->direct_IO(iocb, &data);
+        if (ret > 0) {
+                iocb->ki_pos += ret;
+                iov_iter_advance(to, ret);
+        }
         xfs_rw_iunlock(ip, XFS_IOLOCK_SHARED);
 
+        file_accessed(iocb->ki_filp);
         return ret;
 }