xfs: break up xfs_buf_find() into individual pieces

xfs_buf_find() is made up of three main parts: lookup, insert and
locking. The interactions with xfs_buf_get_map() require it to be
called twice - once for a pure lookup, and again on lookup failure
so the insert path can be run. We want to simplify this down a lot,
so split it into a fast path lookup, a slow path insert and a "lock
the found buffer" helper. This will then let us integrate these
operations more effectively into xfs_buf_get_map() in future
patches.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

fs/xfs/xfs_buf.c

@@ -503,6 +503,98 @@ xfs_buf_hash_destroy(
 	rhashtable_destroy(&pag->pag_buf_hash);
 }
 
+static int
+xfs_buf_map_verify(
+	struct xfs_buftarg	*btp,
+	struct xfs_buf_map	*map)
+{
+	xfs_daddr_t		eofs;
+
+	/* Check for IOs smaller than the sector size / not sector aligned */
+	ASSERT(!(BBTOB(map->bm_len) < btp->bt_meta_sectorsize));
+	ASSERT(!(BBTOB(map->bm_bn) & (xfs_off_t)btp->bt_meta_sectormask));
+
+	/*
+	 * Corrupted block numbers can get through to here, unfortunately, so we
+	 * have to check that the buffer falls within the filesystem bounds.
+	 */
+	eofs = XFS_FSB_TO_BB(btp->bt_mount, btp->bt_mount->m_sb.sb_dblocks);
+	if (map->bm_bn < 0 || map->bm_bn >= eofs) {
+		xfs_alert(btp->bt_mount,
+			  "%s: daddr 0x%llx out of range, EOFS 0x%llx",
+			  __func__, map->bm_bn, eofs);
+		WARN_ON(1);
+		return -EFSCORRUPTED;
+	}
+	return 0;
+}
+
+static int
+xfs_buf_find_lock(
+	struct xfs_buf          *bp,
+	xfs_buf_flags_t		flags)
+{
+	if (!xfs_buf_trylock(bp)) {
+		if (flags & XBF_TRYLOCK) {
+			XFS_STATS_INC(bp->b_mount, xb_busy_locked);
+			xfs_buf_rele(bp);
+			return -EAGAIN;
+		}
+		xfs_buf_lock(bp);
+		XFS_STATS_INC(bp->b_mount, xb_get_locked_waited);
+	}
+
+	/*
+	 * if the buffer is stale, clear all the external state associated with
+	 * it. We need to keep flags such as how we allocated the buffer memory
+	 * intact here.
+	 */
+	if (bp->b_flags & XBF_STALE) {
+		ASSERT((bp->b_flags & _XBF_DELWRI_Q) == 0);
+		bp->b_flags &= _XBF_KMEM | _XBF_PAGES;
+		bp->b_ops = NULL;
+	}
+	return 0;
+}
+
+static inline struct xfs_buf *
+xfs_buf_lookup(
+	struct xfs_perag	*pag,
+	struct xfs_buf_map	*map)
+{
+	struct xfs_buf          *bp;
+
+	bp = rhashtable_lookup(&pag->pag_buf_hash, map, xfs_buf_hash_params);
+	if (!bp)
+		return NULL;
+	atomic_inc(&bp->b_hold);
+	return bp;
+}
+
+/*
+ * Insert the new_bp into the hash table. This consumes the perag reference
+ * taken for the lookup.
+ */
+static int
+xfs_buf_find_insert(
+	struct xfs_buftarg	*btp,
+	struct xfs_perag	*pag,
+	struct xfs_buf		*new_bp)
+{
+	/* No match found */
+	if (!new_bp) {
+		xfs_perag_put(pag);
+		XFS_STATS_INC(btp->bt_mount, xb_miss_locked);
+		return -ENOENT;
+	}
+
+	/* the buffer keeps the perag reference until it is freed */
+	new_bp->b_pag = pag;
+	rhashtable_insert_fast(&pag->pag_buf_hash, &new_bp->b_rhash_head,
+			       xfs_buf_hash_params);
+	return 0;
+}
+
 /*
  * Look up a buffer in the buffer cache and return it referenced and locked
  * in @found_bp.
@@ -533,7 +625,7 @@ xfs_buf_find(
 	struct xfs_perag	*pag;
 	struct xfs_buf		*bp;
 	struct xfs_buf_map	cmap = { .bm_bn = map[0].bm_bn };
-	xfs_daddr_t		eofs;
+	int			error;
 	int			i;
 
 	*found_bp = NULL;
@@ -541,47 +633,22 @@ xfs_buf_find(
 	for (i = 0; i < nmaps; i++)
 		cmap.bm_len += map[i].bm_len;
 
-	/* Check for IOs smaller than the sector size / not sector aligned */
-	ASSERT(!(BBTOB(cmap.bm_len) < btp->bt_meta_sectorsize));
-	ASSERT(!(BBTOB(cmap.bm_bn) & (xfs_off_t)btp->bt_meta_sectormask));
-
-	/*
-	 * Corrupted block numbers can get through to here, unfortunately, so we
-	 * have to check that the buffer falls within the filesystem bounds.
-	 */
-	eofs = XFS_FSB_TO_BB(btp->bt_mount, btp->bt_mount->m_sb.sb_dblocks);
-	if (cmap.bm_bn < 0 || cmap.bm_bn >= eofs) {
-		xfs_alert(btp->bt_mount,
-			  "%s: daddr 0x%llx out of range, EOFS 0x%llx",
-			  __func__, cmap.bm_bn, eofs);
-		WARN_ON(1);
-		return -EFSCORRUPTED;
-	}
+	error = xfs_buf_map_verify(btp, &cmap);
+	if (error)
+		return error;
 
 	pag = xfs_perag_get(btp->bt_mount,
 			    xfs_daddr_to_agno(btp->bt_mount, cmap.bm_bn));
 
 	spin_lock(&pag->pag_buf_lock);
-	bp = rhashtable_lookup_fast(&pag->pag_buf_hash, &cmap,
-				    xfs_buf_hash_params);
-	if (bp) {
-		atomic_inc(&bp->b_hold);
+	bp = xfs_buf_lookup(pag, &cmap);
+	if (bp)
 		goto found;
-	}
 
-	/* No match found */
-	if (!new_bp) {
-		XFS_STATS_INC(btp->bt_mount, xb_miss_locked);
-		spin_unlock(&pag->pag_buf_lock);
-		xfs_perag_put(pag);
-		return -ENOENT;
-	}
-
-	/* the buffer keeps the perag reference until it is freed */
-	new_bp->b_pag = pag;
-	rhashtable_insert_fast(&pag->pag_buf_hash, &new_bp->b_rhash_head,
-			       xfs_buf_hash_params);
+	error = xfs_buf_find_insert(btp, pag, new_bp);
 	spin_unlock(&pag->pag_buf_lock);
+	if (error)
+		return error;
 	*found_bp = new_bp;
 	return 0;
 
@@ -589,26 +656,9 @@ found:
 	spin_unlock(&pag->pag_buf_lock);
 	xfs_perag_put(pag);
 
-	if (!xfs_buf_trylock(bp)) {
-		if (flags & XBF_TRYLOCK) {
-			xfs_buf_rele(bp);
-			XFS_STATS_INC(btp->bt_mount, xb_busy_locked);
-			return -EAGAIN;
-		}
-		xfs_buf_lock(bp);
-		XFS_STATS_INC(btp->bt_mount, xb_get_locked_waited);
-	}
-
-	/*
-	 * if the buffer is stale, clear all the external state associated with
-	 * it. We need to keep flags such as how we allocated the buffer memory
-	 * intact here.
-	 */
-	if (bp->b_flags & XBF_STALE) {
-		ASSERT((bp->b_flags & _XBF_DELWRI_Q) == 0);
-		bp->b_flags &= _XBF_KMEM | _XBF_PAGES;
-		bp->b_ops = NULL;
-	}
+	error = xfs_buf_find_lock(bp, flags);
+	if (error)
+		return error;
 
 	trace_xfs_buf_find(bp, flags, _RET_IP_);
 	XFS_STATS_INC(btp->bt_mount, xb_get_locked);