btrfs-progs: check: repair inode nlink in lowmem

New function repair_inode_nlinks_lowmem() sets nlink of the inode to refs.

If refs equals 0, move the inode to lost+found and set refs to 1
initially.

Signed-off-by: Su Yue <suy.fnst@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>

cmds-check.c

@@ -3018,15 +3018,79 @@ static int get_highest_inode(struct btrfs_trans_handle *trans,
 	return ret;
 }
 
+/*
+ * Link inode to dir 'lost+found'. Increase @ref_count.
+ *
+ * Returns 0 means success.
+ * Returns <0 means failure.
+ */
+static int link_inode_to_lostfound(struct btrfs_trans_handle *trans,
+				   struct btrfs_root *root,
+				   struct btrfs_path *path,
+				   u64 ino, char *namebuf, u32 name_len,
+				   u8 filetype, u64 *ref_count)
+{
+	char *dir_name = "lost+found";
+	u64 lost_found_ino;
+	int ret;
+	u32 mode = 0700;
+
+	btrfs_release_path(path);
+	ret = get_highest_inode(trans, root, path, &lost_found_ino);
+	if (ret < 0)
+		goto out;
+	lost_found_ino++;
+
+	ret = btrfs_mkdir(trans, root, dir_name, strlen(dir_name),
+			  BTRFS_FIRST_FREE_OBJECTID, &lost_found_ino,
+			  mode);
+	if (ret < 0) {
+		error("failed to create '%s' dir: %s", dir_name, strerror(-ret));
+		goto out;
+	}
+	ret = btrfs_add_link(trans, root, ino, lost_found_ino,
+			     namebuf, name_len, filetype, NULL, 1, 0);
+	/*
+	 * Add ".INO" suffix several times to handle case where
+	 * "FILENAME.INO" is already taken by another file.
+	 */
+	while (ret == -EEXIST) {
+		/*
+		 * Conflicting file name, add ".INO" as suffix * +1 for '.'
+		 */
+		if (name_len + count_digits(ino) + 1 > BTRFS_NAME_LEN) {
+			ret = -EFBIG;
+			goto out;
+		}
+		snprintf(namebuf + name_len, BTRFS_NAME_LEN - name_len,
+			 ".%llu", ino);
+		name_len += count_digits(ino) + 1;
+		ret = btrfs_add_link(trans, root, ino, lost_found_ino, namebuf,
+				     name_len, filetype, NULL, 1, 0);
+	}
+	if (ret < 0) {
+		error("failed to link the inode %llu to %s dir: %s",
+		      ino, dir_name, strerror(-ret));
+		goto out;
+	}
+
+	++*ref_count;
+	printf("Moving file '%.*s' to '%s' dir since it has no valid backref\n",
+	       name_len, namebuf, dir_name);
+out:
+	btrfs_release_path(path);
+	if (ret)
+		error("failed to move file '%.*s' to '%s' dir", name_len,
+				namebuf, dir_name);
+	return ret;
+}
+
 static int repair_inode_nlinks(struct btrfs_trans_handle *trans,
 			       struct btrfs_root *root,
 			       struct btrfs_path *path,
 			       struct inode_record *rec)
 {
-	char *dir_name = "lost+found";
 	char namebuf[BTRFS_NAME_LEN] = {0};
-	u64 lost_found_ino;
-	u32 mode = 0700;
 	u8 type = 0;
 	int namelen = 0;
 	int name_recovered = 0;
@@ -3063,55 +3127,11 @@ static int repair_inode_nlinks(struct btrfs_trans_handle *trans,
 	}
 
 	if (rec->found_link == 0) {
-		ret = get_highest_inode(trans, root, path, &lost_found_ino);
+		ret = link_inode_to_lostfound(trans, root, path, rec->ino,
-		if (ret < 0)
+					      namebuf, namelen, type,
+					      (u64 *)&rec->found_link);
+		if (ret)
 			goto out;
-		lost_found_ino++;
-		ret = btrfs_mkdir(trans, root, dir_name, strlen(dir_name),
-				  BTRFS_FIRST_FREE_OBJECTID, &lost_found_ino,
-				  mode);
-		if (ret < 0) {
-			fprintf(stderr, "Failed to create '%s' dir: %s\n",
-				dir_name, strerror(-ret));
-			goto out;
-		}
-		ret = btrfs_add_link(trans, root, rec->ino, lost_found_ino,
-				     namebuf, namelen, type, NULL, 1, 0);
-		/*
-		 * Add ".INO" suffix several times to handle case where
-		 * "FILENAME.INO" is already taken by another file.
-		 */
-		while (ret == -EEXIST) {
-			/*
-			 * Conflicting file name, add ".INO" as suffix * +1 for '.'
-			 */
-			if (namelen + count_digits(rec->ino) + 1 >
-			    BTRFS_NAME_LEN) {
-				ret = -EFBIG;
-				goto out;
-			}
-			snprintf(namebuf + namelen, BTRFS_NAME_LEN - namelen,
-				 ".%llu", rec->ino);
-			namelen += count_digits(rec->ino) + 1;
-			ret = btrfs_add_link(trans, root, rec->ino,
-					     lost_found_ino, namebuf,
-					     namelen, type, NULL, 1, 0);
-		}
-		if (ret < 0) {
-			fprintf(stderr,
-				"Failed to link the inode %llu to %s dir: %s\n",
-				rec->ino, dir_name, strerror(-ret));
-			goto out;
-		}
-		/*
-		 * Just increase the found_link, don't actually add the
-		 * backref. This will make things easier and this inode
-		 * record will be freed after the repair is done.
-		 * So fsck will not report problem about this inode.
-		 */
-		rec->found_link++;
-		printf("Moving file '%.*s' to '%s' dir since it has no valid backref\n",
-		       namelen, namebuf, dir_name);
 	}
 	printf("Fixed the nlink of inode %llu\n", rec->ino);
 out:
@@ -5592,6 +5612,92 @@ out:
 	return err;
 }
 
+/* Set inode_item nlink to @ref_count.
+ * If @ref_count == 0, move it to "lost+found" and increase @ref_count.
+ *
+ * Returns 0 on success
+ */
+static int repair_inode_nlinks_lowmem(struct btrfs_root *root,
+				      struct btrfs_path *path, u64 ino,
+				      const char *name, u32 namelen,
+				      u64 ref_count, u8 filetype, u64 *nlink)
+{
+	struct btrfs_trans_handle *trans;
+	struct btrfs_inode_item *ii;
+	struct btrfs_key key;
+	struct btrfs_key old_key;
+	char namebuf[BTRFS_NAME_LEN] = {0};
+	int name_len;
+	int ret;
+	int ret2;
+
+	/* save the key */
+	btrfs_item_key_to_cpu(path->nodes[0], &old_key, path->slots[0]);
+
+	if (name && namelen) {
+		ASSERT(namelen <= BTRFS_NAME_LEN);
+		memcpy(namebuf, name, namelen);
+		name_len = namelen;
+	} else {
+		sprintf(namebuf, "%llu", ino);
+		name_len = count_digits(ino);
+		printf("Can't find file name for inode %llu, use %s instead\n",
+		       ino, namebuf);
+	}
+
+	trans = btrfs_start_transaction(root, 1);
+	if (IS_ERR(trans)) {
+		ret = PTR_ERR(trans);
+		goto out;
+	}
+
+	btrfs_release_path(path);
+	/* if refs is 0, put it into lostfound */
+	if (ref_count == 0) {
+		ret = link_inode_to_lostfound(trans, root, path, ino, namebuf,
+					      name_len, filetype, &ref_count);
+		if (ret)
+			goto fail;
+	}
+
+	/* reset inode_item's nlink to ref_count */
+	key.objectid = ino;
+	key.type = BTRFS_INODE_ITEM_KEY;
+	key.offset = 0;
+
+	btrfs_release_path(path);
+	ret = btrfs_search_slot(trans, root, &key, path, 0, 1);
+	if (ret > 0)
+		ret = -ENOENT;
+	if (ret)
+		goto fail;
+
+	ii = btrfs_item_ptr(path->nodes[0], path->slots[0],
+			    struct btrfs_inode_item);
+	btrfs_set_inode_nlink(path->nodes[0], ii, ref_count);
+	btrfs_mark_buffer_dirty(path->nodes[0]);
+
+	if (nlink)
+		*nlink = ref_count;
+fail:
+	btrfs_commit_transaction(trans, root);
+out:
+	if (ret)
+		error(
+	"fail to repair nlink of inode %llu root %llu name %s filetype %u",
+		       root->objectid, ino, namebuf, filetype);
+	else
+		printf("Fixed nlink of inode %llu root %llu name %s filetype %u\n",
+		       root->objectid, ino, namebuf, filetype);
+
+	/* research */
+	btrfs_release_path(path);
+	ret2 = btrfs_search_slot(NULL, root, &old_key, path, 0, 0);
+	if (ret2 < 0)
+		return ret |= ret2;
+	return ret;
+}
+
 /*
  * Check INODE_ITEM and related ITEMs (the same inode number)
  * 1. check link count
@@ -5715,6 +5821,13 @@ out:
 			err &= ~DIR_COUNT_AGAIN;
 			count_dir_isize(root, inode_id, &size);
 		}
+
+		if ((nlink != 1 || refs != 1) && repair) {
+			ret = repair_inode_nlinks_lowmem(root, path, inode_id,
+				namebuf, name_len, refs, imode_to_type(mode),
+				&nlink);
+		}
+
 		if (nlink != 1) {
 			err |= LINK_COUNT_ERROR;
 			error("root %llu DIR INODE[%llu] shouldn't have more than one link(%llu)",
@@ -5744,9 +5857,16 @@ out:
 		}
 	} else {
 		if (nlink != refs) {
-			err |= LINK_COUNT_ERROR;
+			if (repair)
-			error("root %llu INODE[%llu] nlink(%llu) not equal to inode_refs(%llu)",
+				ret = repair_inode_nlinks_lowmem(root, path,
-			      root->objectid, inode_id, nlink, refs);
+					 inode_id, namebuf, name_len, refs,
+					 imode_to_type(mode), &nlink);
+			if (!repair || ret) {
+				err |= LINK_COUNT_ERROR;
+				error(
+		"root %llu INODE[%llu] nlink(%llu) not equal to inode_refs(%llu)",
+				      root->objectid, inode_id, nlink, refs);
+			}
 		} else if (!nlink) {
 			if (repair)
 				ret = repair_inode_orphan_item_lowmem(root,