xfs: flag all buffers as metadata

Now that REQ_META bios aren't treated specially in the CFQ I/O schedule
anymore, we can tag all buffers as metadata to make blktrace traces more
meaningful.  Note that we use buffers also to zero out partial blocks
in the preallocation / hole punching code, and while they operate on
data blocks the zeros written certainly aren't data.  I think this case
is borderline metadata enough to not bother special casing it.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alex Elder <aelder@sgi.com>

fs/xfs/linux-2.6/xfs_buf.c

@@ -1224,6 +1224,9 @@ _xfs_buf_ioapply(
 		rw = READ;
 	}
 
+	/* we only use the buffer cache for meta-data */
+	rw |= REQ_META;
+
 next_chunk:
 	atomic_inc(&bp->b_io_remaining);
 	nr_pages = BIO_MAX_SECTORS >> (PAGE_SHIFT - BBSHIFT);