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>

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index fdb123f..440bb8b 100644 (file)
--- 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;
 }