xfs: simplify xfs_buf_get / xfs_buf_read interfaces

Currently the low-level buffer cache interfaces are highly confusing
as we have a _flags variant of each that does actually respect the
flags, and one without _flags which has a flags argument that gets
ignored and overriden with a default set.  Given that very few places
use the default arguments get rid of the duplication and convert all
callers to pass the flags explicitly.  Also remove the now confusing
_flags postfix.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <david@fromorbit.com>
Signed-off-by: Alex Elder <aelder@sgi.com>
diff --git a/fs/xfs/xfs_rw.c b/fs/xfs/xfs_rw.c
index 3f816ad..6fa1089 100644
--- a/fs/xfs/xfs_rw.c
+++ b/fs/xfs/xfs_rw.c
@@ -277,10 +277,10 @@
 	xfs_buf_t	 *bp;
 	int		 error;
 
-	if (flags)
-		bp = xfs_buf_read_flags(target, blkno, len, flags);
-	else
-		bp = xfs_buf_read(target, blkno, len, flags);
+	if (!flags)
+		flags = XBF_LOCK | XBF_MAPPED;
+
+	bp = xfs_buf_read(target, blkno, len, flags);
 	if (!bp)
 		return XFS_ERROR(EIO);
 	error = XFS_BUF_GETERROR(bp);