xfs: rename buffer cache index variable b_bn

To stop external users from using b_bn as the disk address of the
buffer, rename it to b_rhash_key to indicate that it is the buffer
cache index, not the block number of the buffer. Code that needs the
disk address should use xfs_buf_daddr() to obtain it.

Do the rename and clean up any of the remaining internal b_bn users.
Also clean up any remaining b_bn cruft that is now unused.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index c1bb6e4..047bd6e 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -251,7 +251,7 @@
 		return error;
 	}
 
-	bp->b_bn = map[0].bm_bn;
+	bp->b_rhash_key = map[0].bm_bn;
 	bp->b_length = 0;
 	for (i = 0; i < nmaps; i++) {
 		bp->b_maps[i].bm_bn = map[i].bm_bn;
@@ -459,7 +459,7 @@
 	 */
 	BUILD_BUG_ON(offsetof(struct xfs_buf_map, bm_bn) != 0);
 
-	if (bp->b_bn != map->bm_bn)
+	if (bp->b_rhash_key != map->bm_bn)
 		return 1;
 
 	if (unlikely(bp->b_length != map->bm_len)) {
@@ -481,7 +481,7 @@
 	.min_size		= 32,	/* empty AGs have minimal footprint */
 	.nelem_hint		= 16,
 	.key_len		= sizeof(xfs_daddr_t),
-	.key_offset		= offsetof(struct xfs_buf, b_bn),
+	.key_offset		= offsetof(struct xfs_buf, b_rhash_key),
 	.head_offset		= offsetof(struct xfs_buf, b_rhash_head),
 	.automatic_shrinking	= true,
 	.obj_cmpfn		= _xfs_buf_obj_cmp,
@@ -853,7 +853,9 @@
 
 /*
  * Read an uncached buffer from disk. Allocates and returns a locked
- * buffer containing the disk contents or nothing.
+ * buffer containing the disk contents or nothing. Uncached buffers always have
+ * a cache index of XFS_BUF_DADDR_NULL so we can easily determine if the buffer
+ * is cached or uncached during fault diagnosis.
  */
 int
 xfs_buf_read_uncached(
@@ -875,7 +877,7 @@
 
 	/* set up the buffer for a read IO */
 	ASSERT(bp->b_map_count == 1);
-	bp->b_bn = XFS_BUF_DADDR_NULL;  /* always null for uncached buffers */
+	bp->b_rhash_key = XFS_BUF_DADDR_NULL;
 	bp->b_maps[0].bm_bn = daddr;
 	bp->b_flags |= XBF_READ;
 	bp->b_ops = ops;
@@ -1513,7 +1515,7 @@
 						   SHUTDOWN_CORRUPT_INCORE);
 				return;
 			}
-		} else if (bp->b_bn != XFS_BUF_DADDR_NULL) {
+		} else if (bp->b_rhash_key != XFS_BUF_DADDR_NULL) {
 			struct xfs_mount *mp = bp->b_mount;
 
 			/*
@@ -1523,7 +1525,8 @@
 			if (xfs_has_crc(mp)) {
 				xfs_warn(mp,
 					"%s: no buf ops on daddr 0x%llx len %d",
-					__func__, bp->b_bn, bp->b_length);
+					__func__, xfs_buf_daddr(bp),
+					bp->b_length);
 				xfs_hex_dump(bp->b_addr,
 						XFS_CORRUPTION_DUMP_LEN);
 				dump_stack();
@@ -1793,7 +1796,7 @@
 				xfs_buf_alert_ratelimited(bp,
 					"XFS: Corruption Alert",
 "Corruption Alert: Buffer at daddr 0x%llx had permanent write failures!",
-					(long long)bp->b_bn);
+					(long long)xfs_buf_daddr(bp));
 			}
 			xfs_buf_rele(bp);
 		}
diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h
index 6db2fba..6b0200b 100644
--- a/fs/xfs/xfs_buf.h
+++ b/fs/xfs/xfs_buf.h
@@ -134,11 +134,7 @@
 	 */
 	struct rhash_head	b_rhash_head;	/* pag buffer hash node */
 
-	/*
-	 * b_bn is the cache index. Do not use directly, use b_maps[0].bm_bn
-	 * for the buffer disk address instead.
-	 */
-	xfs_daddr_t		b_bn;
+	xfs_daddr_t		b_rhash_key;	/* buffer cache index */
 	int			b_length;	/* size of buffer in BBs */
 	atomic_t		b_hold;		/* reference count */
 	atomic_t		b_lru_ref;	/* lru reclaim ref count */
@@ -301,18 +297,6 @@
 extern int xfs_buf_init(void);
 extern void xfs_buf_terminate(void);
 
-/*
- * These macros use the IO block map rather than b_bn. b_bn is now really
- * just for the buffer cache index for cached buffers. As IO does not use b_bn
- * anymore, uncached buffers do not use b_bn at all and hence must modify the IO
- * map directly. Uncached buffers are not allowed to be discontiguous, so this
- * is safe to do.
- *
- * In future, uncached buffers will pass the block number directly to the io
- * request function and hence these macros will go away at that point.
- */
-#define XFS_BUF_SET_ADDR(bp, bno)	((bp)->b_maps[0].bm_bn = (xfs_daddr_t)(bno))
-
 static inline xfs_daddr_t xfs_buf_daddr(struct xfs_buf *bp)
 {
 	return bp->b_maps[0].bm_bn;