xfs: refactor unlinked list search and mapping to a separate function

There's a loop that searches an unlinked bucket list to find the inode
that points to a given inode.  Hoist this into a separate function;
later we'll use our iunlink backref cache to bypass the slow list
operation.  No functional changes.
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>

fs/xfs/xfs_inode.c

@@ -2082,6 +2082,97 @@ xfs_iunlink(
 	return xfs_iunlink_update_bucket(tp, agno, agibp, bucket_index, agino);
 }
 
+/* Return the imap, dinode pointer, and buffer for an inode. */
+STATIC int
+xfs_iunlink_map_ino(
+	struct xfs_trans	*tp,
+	xfs_agnumber_t		agno,
+	xfs_agino_t		agino,
+	struct xfs_imap		*imap,
+	struct xfs_dinode	**dipp,
+	struct xfs_buf		**bpp)
+{
+	struct xfs_mount	*mp = tp->t_mountp;
+	int			error;
+
+	imap->im_blkno = 0;
+	error = xfs_imap(mp, tp, XFS_AGINO_TO_INO(mp, agno, agino), imap, 0);
+	if (error) {
+		xfs_warn(mp, "%s: xfs_imap returned error %d.",
+				__func__, error);
+		return error;
+	}
+
+	error = xfs_imap_to_bp(mp, tp, imap, dipp, bpp, 0, 0);
+	if (error) {
+		xfs_warn(mp, "%s: xfs_imap_to_bp returned error %d.",
+				__func__, error);
+		return error;
+	}
+
+	return 0;
+}
+
+/*
+ * Walk the unlinked chain from @head_agino until we find the inode that
+ * points to @target_agino.  Return the inode number, map, dinode pointer,
+ * and inode cluster buffer of that inode as @agino, @imap, @dipp, and @bpp.
+ *
+ * @tp, @pag, @head_agino, and @target_agino are input parameters.
+ * @agino, @imap, @dipp, and @bpp are all output parameters.
+ *
+ * Do not call this function if @target_agino is the head of the list.
+ */
+STATIC int
+xfs_iunlink_map_prev(
+	struct xfs_trans	*tp,
+	xfs_agnumber_t		agno,
+	xfs_agino_t		head_agino,
+	xfs_agino_t		target_agino,
+	xfs_agino_t		*agino,
+	struct xfs_imap		*imap,
+	struct xfs_dinode	**dipp,
+	struct xfs_buf		**bpp)
+{
+	struct xfs_mount	*mp = tp->t_mountp;
+	xfs_agino_t		next_agino;
+	int			error;
+
+	ASSERT(head_agino != target_agino);
+	*bpp = NULL;
+
+	next_agino = head_agino;
+	while (next_agino != target_agino) {
+		xfs_agino_t	unlinked_agino;
+
+		if (*bpp)
+			xfs_trans_brelse(tp, *bpp);
+
+		*agino = next_agino;
+		error = xfs_iunlink_map_ino(tp, agno, next_agino, imap, dipp,
+				bpp);
+		if (error)
+			return error;
+
+		unlinked_agino = be32_to_cpu((*dipp)->di_next_unlinked);
+		/*
+		 * Make sure this pointer is valid and isn't an obvious
+		 * infinite loop.
+		 */
+		if (!xfs_verify_agino(mp, agno, unlinked_agino) ||
+		    next_agino == unlinked_agino) {
+			XFS_CORRUPTION_ERROR(__func__,
+					XFS_ERRLEVEL_LOW, mp,
+					*dipp, sizeof(**dipp));
+			error = -EFSCORRUPTED;
+			return error;
+		}
+		next_agino = unlinked_agino;
+	}
+
+	return 0;
+}
+
 /*
  * Pull the on-disk inode from the AGI unlinked list.
  */
@@ -2095,7 +2186,6 @@ xfs_iunlink_remove(
 	struct xfs_buf		*agibp;
 	struct xfs_buf		*last_ibp;
 	struct xfs_dinode	*last_dip = NULL;
-	xfs_ino_t		next_ino;
 	xfs_agnumber_t		agno = XFS_INO_TO_AGNO(mp, ip->i_ino);
 	xfs_agino_t		agino = XFS_INO_TO_AGINO(mp, ip->i_ino);
 	xfs_agino_t		next_agino;
@@ -2138,43 +2228,11 @@ xfs_iunlink_remove(
 		struct xfs_imap	imap;
 		xfs_agino_t	prev_agino;
 
-		/*
-		 * We need to search the list for the inode being freed.
-		 */
-		last_ibp = NULL;
-		while (next_agino != agino) {
-			if (last_ibp)
-				xfs_trans_brelse(tp, last_ibp);
-
-			imap.im_blkno = 0;
-			next_ino = XFS_AGINO_TO_INO(mp, agno, next_agino);
-
-			error = xfs_imap(mp, tp, next_ino, &imap, 0);
-			if (error) {
-				xfs_warn(mp,
-	"%s: xfs_imap returned error %d.",
-					 __func__, error);
-				return error;
-			}
-
-			error = xfs_imap_to_bp(mp, tp, &imap, &last_dip,
-					       &last_ibp, 0, 0);
-			if (error) {
-				xfs_warn(mp,
-	"%s: xfs_imap_to_bp returned error %d.",
-					__func__, error);
-				return error;
-			}
-
-			prev_agino = next_agino;
-			next_agino = be32_to_cpu(last_dip->di_next_unlinked);
-			if (!xfs_verify_agino(mp, agno, next_agino)) {
-				XFS_CORRUPTION_ERROR(__func__,
-						XFS_ERRLEVEL_LOW, mp,
-						last_dip, sizeof(*last_dip));
-				return -EFSCORRUPTED;
-			}
-		}
+		/* We need to search the list for the inode being freed. */
+		error = xfs_iunlink_map_prev(tp, agno, next_agino, agino,
+				&prev_agino, &imap, &last_dip, &last_ibp);
+		if (error)
+			return error;
 
 		/*
 		 * Now last_ibp points to the buffer previous to us on the