[RFC PATCH mtd-utils 067/110] fsck.ubifs: rebuild_fs: Extract reachable directory entries tree

[Zhihao Cheng]

This is the 5/12 step of rebuilding. Extract reachable directory entries
tree. Make sure that all files can be searched from '/', unreachable
file is deleted. So, all files can be accessible in userspace after
reparing.

Signed-off-by: Zhihao Cheng <chengzhihao1@xxxxxxxxxx>
---
 ubifs-utils/fsck.ubifs/extract_files.c | 94 ++++++++++++++++++++++++++++++++++
 ubifs-utils/fsck.ubifs/fsck.ubifs.h    |  6 +++
 ubifs-utils/fsck.ubifs/rebuild_fs.c    | 44 ++++++++++++++++
 3 files changed, 144 insertions(+)

diff --git a/ubifs-utils/fsck.ubifs/extract_files.c b/ubifs-utils/fsck.ubifs/extract_files.c
index 772e3003..dd5cb310 100644
--- a/ubifs-utils/fsck.ubifs/extract_files.c
+++ b/ubifs-utils/fsck.ubifs/extract_files.c
@@ -525,6 +525,7 @@ static int update_file(struct ubifs_info *c, struct scanned_file *file,
 	{
 		struct scanned_dent_node *dent = (struct scanned_dent_node *)sn;
 
+		dent->file = file;
 		err = insert_file_dentry(file, dent);
 		break;
 	}
@@ -888,3 +889,96 @@ check_dent_node:
 
 	return true;
 }
+
+static bool dentry_is_reachable(struct ubifs_info *c,
+				struct scanned_dent_node *dent_node,
+				struct list_head *path_list,
+				struct rb_root *file_tree)
+{
+	struct scanned_file *parent_file = NULL;
+	struct scanned_dent_node *dn, *parent_dent;
+	struct rb_node *p;
+
+	/* Check whether the path is cyclical. */
+	list_for_each_entry(dn, path_list, list) {
+		if (dn == dent_node)
+			return false;
+	}
+
+	/* Quick path, dentry has already been checked as reachable. */
+	if (dent_node->can_be_found)
+		return true;
+
+	dent_node->can_be_found = true;
+	list_add(&dent_node->list, path_list);
+
+	parent_file = lookup_file(file_tree, key_inum(c, &dent_node->key));
+	/* Parent dentry is not found, unreachable. */
+	if (!parent_file)
+		return false;
+
+	/* Parent dentry is '/', reachable. */
+	if (parent_file->inum == UBIFS_ROOT_INO)
+		return true;
+
+	p = rb_first(&parent_file->dent_nodes);
+	if (!p)
+		return false;
+	parent_dent = rb_entry(p, struct scanned_dent_node, rb);
+
+	return dentry_is_reachable(c, parent_dent, path_list, file_tree);
+}
+
+/**
+ * file_is_reachable - whether the file can be found from '/'.
+ * @c: UBIFS file-system description object
+ * @file: file object
+ * @file_tree: tree of all scanned files
+ *
+ * This function iterates all directory entries in given @file and checks
+ * whether each dentry is reachable. All unreachable directory entries will
+ * be removed.
+ */
+bool file_is_reachable(struct ubifs_info *c, struct scanned_file *file,
+		       struct rb_root *file_tree)
+{
+	struct rb_node *node;
+	struct scanned_dent_node *dent_node;
+
+	if (file->inum == UBIFS_ROOT_INO)
+		goto reachable;
+
+retry:
+	for (node = rb_first(&file->dent_nodes); node; node = rb_next(node)) {
+		LIST_HEAD(path_list);
+
+		dent_node = rb_entry(node, struct scanned_dent_node, rb);
+
+		if (dentry_is_reachable(c, dent_node, &path_list, file_tree))
+			continue;
+
+		while (!list_empty(&path_list)) {
+			dent_node = list_entry(path_list.next,
+					       struct scanned_dent_node, list);
+
+			dbg_fsck("remove unreachable dentry %s, in %s",
+				 c->encrypted && !file->ino.is_xattr ?
+				 "<encrypted>" : dent_node->name, c->dev_name);
+			list_del(&dent_node->list);
+			rb_erase(&dent_node->rb, &dent_node->file->dent_nodes);
+			kfree(dent_node);
+		}
+
+		/* Since dentry node is removed from rb-tree, rescan rb-tree. */
+		goto retry;
+	}
+
+	if (!rb_first(&file->dent_nodes)) {
+		dbg_fsck("file %lu is unreachable, in %s", file->inum, c->dev_name);
+		return false;
+	}
+
+reachable:
+	dbg_fsck("file %lu is reachable, in %s", file->inum, c->dev_name);
+	return true;
+}
diff --git a/ubifs-utils/fsck.ubifs/fsck.ubifs.h b/ubifs-utils/fsck.ubifs/fsck.ubifs.h
index 3885d138..d378a06c 100644
--- a/ubifs-utils/fsck.ubifs/fsck.ubifs.h
+++ b/ubifs-utils/fsck.ubifs/fsck.ubifs.h
@@ -39,6 +39,8 @@ enum { NORMAL_MODE = 0, SAFE_MODE, DANGER_MODE0,
 /* Types of inconsistent problems */
 enum { SB_CORRUPTED = 0 };
 
+struct scanned_file;
+
 /**
  * scanned_node - common header node.
  * @exist: whether the node is found by scanning
@@ -92,6 +94,7 @@ struct scanned_ino_node {
  * @nlen: name length
  * @name: dentry name
  * @inum: target inode number
+ * @file: corresponding file
  * @rb: link in the trees of:
  *  1) valid dentry nodes or deleted dentry node
  *  2) all scanned dentry nodes from same file
@@ -105,6 +108,7 @@ struct scanned_dent_node {
 	unsigned int nlen;
 	char name[UBIFS_MAX_NLEN + 1];
 	ino_t inum;
+	struct scanned_file *file;
 	struct rb_node rb;
 	struct list_head list;
 };
@@ -266,6 +270,8 @@ void destroy_file_tree(struct ubifs_info *c, struct rb_root *file_tree);
 struct scanned_file *lookup_file(struct rb_root *file_tree, ino_t inum);
 bool file_is_valid(struct ubifs_info *c, struct scanned_file *file,
 		   struct rb_root *file_tree);
+bool file_is_reachable(struct ubifs_info *c, struct scanned_file *file,
+		       struct rb_root *file_tree);
 
 /* rebuild_fs.c */
 int ubifs_rebuild_filesystem(struct ubifs_info *c);
diff --git a/ubifs-utils/fsck.ubifs/rebuild_fs.c b/ubifs-utils/fsck.ubifs/rebuild_fs.c
index 31f1b3ba..669b61d1 100644
--- a/ubifs-utils/fsck.ubifs/rebuild_fs.c
+++ b/ubifs-utils/fsck.ubifs/rebuild_fs.c
@@ -588,6 +588,46 @@ static void filter_invalid_files(struct ubifs_info *c)
 }
 
 /**
+ * extract_dentry_tree - extract reachable directory entries.
+ * @c: UBIFS file-system description object
+ *
+ * This function iterates all directory entries and remove those
+ * unreachable ones. 'Unreachable' means that a directory entry can
+ * not be searched from '/'.
+ */
+static void extract_dentry_tree(struct ubifs_info *c)
+{
+	struct rb_node *node;
+	struct scanned_file *file;
+	struct rb_root *tree = &FSCK(c)->rebuild->scanned_files;
+	LIST_HEAD(unreachable);
+
+	for (node = rb_first(tree); node; node = rb_next(node)) {
+		file = rb_entry(node, struct scanned_file, rb);
+
+		/*
+		 * Since all xattr files are already attached to corresponding
+		 * host file, there are only non-xattr files in the file tree.
+		 */
+		ubifs_assert(c, !file->ino.is_xattr);
+		if (!file_is_reachable(c, file, tree))
+			list_add(&file->list, &unreachable);
+	}
+
+	/* Remove unreachable files. */
+	while (!list_empty(&unreachable)) {
+		file = list_entry(unreachable.next, struct scanned_file, list);
+
+		dbg_fsck("remove unreachable file %lu, in %s",
+			 file->inum, c->dev_name);
+		list_del(&file->list);
+		destroy_file_content(c, file);
+		rb_erase(&file->rb, tree);
+		kfree(file);
+	}
+}
+
+/**
  * ubifs_rebuild_filesystem - Rebuild filesystem.
  * @c: UBIFS file-system description object
  *
@@ -633,6 +673,10 @@ int ubifs_rebuild_filesystem(struct ubifs_info *c)
 	log_out(c, "Filter invalid files");
 	filter_invalid_files(c);
 
+	/* Step 5: Extract reachable directory entries. */
+	log_out(c, "Extract reachable files");
+	extract_dentry_tree(c);
+
 out:
 	destroy_scanned_info(c, &si);
 	destroy_rebuild_info(c);
-- 
2.13.6