[PATCH 1/4] btrfs-progs: mode-lowmem: Fix false alert about orphan inode

[Qu Wenruo <wqu@suse.com>]

Btrfs can delay inode deletion and in that case btrfs will unlink the
victim inode from its parent dir, and insert a marker to info btrfs to
delete it later.

In that case, such victim inode will have nlinks == 0, but is still
completely valid.
Original mode won't report such problem, but lowmem mode doesn't check
the ORPHAN_ITEM key for such inode, and can report false alert like:
------
ERROR: root 257 INODE[28891726] is orphan item
------

Fix such false alert by checking orphan item for inode whose nlink is 0.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 check/mode-lowmem.c | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/check/mode-lowmem.c b/check/mode-lowmem.c
index 62bcf3d2e126..b11a6d77d102 100644
--- a/check/mode-lowmem.c
+++ b/check/mode-lowmem.c
@@ -1861,6 +1861,24 @@ out:
 	return ret;
 }
 
+static bool has_orphan_item(struct btrfs_root *root, u64 ino)
+{
+	struct btrfs_path path;
+	struct btrfs_key key;
+	int ret;
+
+	btrfs_init_path(&path);
+	key.objectid = BTRFS_ORPHAN_OBJECTID;
+	key.type = BTRFS_ORPHAN_ITEM_KEY;
+	key.offset = ino;
+
+	ret = btrfs_search_slot(NULL, root, &key, &path, 0, 0);
+	btrfs_release_path(&path);
+	if (ret == 0)
+		return true;
+	return false;
+}
+
 /*
  * Check INODE_ITEM and related ITEMs (the same inode number)
  * 1. check link count
@@ -1890,6 +1908,7 @@ static int check_inode_item(struct btrfs_root *root, struct btrfs_path *path,
 	u64 extent_size = 0;
 	unsigned int dir;
 	unsigned int nodatasum;
+	bool is_orphan = false;
 	int slot;
 	int ret;
 	int err = 0;
@@ -2040,10 +2059,11 @@ out:
 				      root->objectid, inode_id, nlink, refs);
 			}
 		} else if (!nlink) {
-			if (repair)
+			is_orphan = has_orphan_item(root, inode_id);
+			if (!is_orphan && repair)
 				ret = repair_inode_orphan_item_lowmem(root,
 							      path, inode_id);
-			if (!repair || ret) {
+			if (!is_orphan && (!repair || ret)) {
 				err |= ORPHAN_ITEM;
 				error("root %llu INODE[%llu] is orphan item",
 				      root->objectid, inode_id);
-- 
2.16.1