Add support for '.' and '..' entries in sqfs_dir_reader_t

Two flags are added to the dir reader API, one for the create function
that the dir reader should report those entries and one to the open
function to suppress that if it was enabled.

To implement the feature, a mapping of visited directory inodes is
maintained internally, that mapps inode numbers to inode references.

When opening a directory, state is maintained to generate the fake
entries for '.' and '..'. Since all the other functions are based on
the open/read/rewind API, no alterations need to be made. The tree
scan function is modified, to use the suppress flag, so it does not
accidentally catch those entries.

Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>

5 files changed, 257 insertions, 24 deletions

diff --git a/lib/sqfs/Makemodule.am b/lib/sqfs/Makemodule.am
index c37301b..06ffea1 100644
--- a/lib/sqfs/Makemodule.am
+++ b/lib/sqfs/Makemodule.am
@@ -33,7 +33,7 @@ libsquashfs_la_SOURCES += lib/sqfs/block_processor/block_processor.c
 libsquashfs_la_SOURCES += lib/sqfs/block_processor/backend.c
 libsquashfs_la_SOURCES += lib/sqfs/frag_table.c include/sqfs/frag_table.h
 libsquashfs_la_SOURCES += lib/sqfs/block_writer.c include/sqfs/block_writer.h
-libsquashfs_la_SOURCES += lib/sqfs/misc.c
+libsquashfs_la_SOURCES += lib/sqfs/misc.c lib/sqfs/dir_reader/dcache.c
 libsquashfs_la_CPPFLAGS = $(AM_CPPFLAGS)
 libsquashfs_la_LDFLAGS = $(AM_LDFLAGS) -version-info $(LIBSQUASHFS_SO_VERSION)
 libsquashfs_la_CFLAGS = $(AM_CFLAGS) $(PTHREAD_CFLAGS) $(ZLIB_CFLAGS)
diff --git a/lib/sqfs/dir_reader/dcache.c b/lib/sqfs/dir_reader/dcache.c
new file mode 100644
index 0000000..47fbf73
--- /dev/null
+++ b/lib/sqfs/dir_reader/dcache.c
@@ -0,0 +1,73 @@
+/* SPDX-License-Identifier: LGPL-3.0-or-later */
+/*
+ * dcache.c
+ *
+ * Copyright (C) 2019 David Oberhollenzer <goliath@infraroot.at>
+ */
+#define SQFS_BUILDING_DLL
+#include "internal.h"
+
+static int dcache_key_compare(const void *ctx, const void *l, const void *r)
+{
+	sqfs_u32 lhs = *((const sqfs_u32 *)l), rhs = *((const sqfs_u32 *)r);
+	(void)ctx;
+
+	return lhs < rhs ? -1 : (lhs > rhs ? 1 : 0);
+}
+
+int sqfs_dir_reader_dcache_init(sqfs_dir_reader_t *rd, sqfs_u32 flags)
+{
+	if (!(flags & SQFS_DIR_READER_DOT_ENTRIES))
+		return 0;
+
+	return rbtree_init(&rd->dcache, sizeof(sqfs_u32), sizeof(sqfs_u64),
+			   dcache_key_compare);
+}
+
+int sqfs_dir_reader_dcache_init_copy(sqfs_dir_reader_t *copy,
+				     const sqfs_dir_reader_t *rd)
+{
+	if (!(rd->flags & SQFS_DIR_READER_DOT_ENTRIES))
+		return 0;
+
+	return rbtree_copy(&rd->dcache, &copy->dcache);
+}
+
+void sqfs_dir_reader_dcache_cleanup(sqfs_dir_reader_t *rd)
+{
+	if (!(rd->flags & SQFS_DIR_READER_DOT_ENTRIES))
+		return;
+
+	rbtree_cleanup(&rd->dcache);
+}
+
+int sqfs_dir_reader_dcache_add(sqfs_dir_reader_t *rd,
+			       sqfs_u32 inode, sqfs_u64 ref)
+{
+	rbtree_node_t *node;
+
+	if (!(rd->flags & SQFS_DIR_READER_DOT_ENTRIES))
+		return 0;
+
+	node = rbtree_lookup(&rd->dcache, &inode);
+	if (node != NULL)
+		return 0;
+
+	return rbtree_insert(&rd->dcache, &inode, &ref);
+}
+
+int sqfs_dir_reader_dcache_find(sqfs_dir_reader_t *rd,
+				sqfs_u32 inode, sqfs_u64 *ref)
+{
+	rbtree_node_t *node;
+
+	if (!(rd->flags & SQFS_DIR_READER_DOT_ENTRIES))
+		return SQFS_ERROR_NO_ENTRY;
+
+	node = rbtree_lookup(&rd->dcache, &inode);
+	if (node == NULL)
+		return SQFS_ERROR_NO_ENTRY;
+
+	*ref = *((sqfs_u64 *)rbtree_node_value(node));
+	return 0;
+}
diff --git a/lib/sqfs/dir_reader/dir_reader.c b/lib/sqfs/dir_reader/dir_reader.c
index 969b71d..8a074aa 100644
--- a/lib/sqfs/dir_reader/dir_reader.c
+++ b/lib/sqfs/dir_reader/dir_reader.c
@@ -11,6 +11,7 @@ static void dir_reader_destroy(sqfs_object_t *obj)
 {
 	sqfs_dir_reader_t *rd = (sqfs_dir_reader_t *)obj;
 
+	sqfs_dir_reader_dcache_cleanup(rd);
 	sqfs_destroy(rd->meta_inode);
 	sqfs_destroy(rd->meta_dir);
 	free(rd);
@@ -26,6 +27,9 @@ static sqfs_object_t *dir_reader_copy(const sqfs_object_t *obj)
 
 	memcpy(copy, rd, sizeof(*copy));
 
+	if (sqfs_dir_reader_dcache_init_copy(copy, rd))
+		goto fail_cache;
+
 	copy->meta_inode = sqfs_copy(rd->meta_inode);
 	if (copy->meta_inode == NULL)
 		goto fail_mino;
@@ -38,6 +42,8 @@ static sqfs_object_t *dir_reader_copy(const sqfs_object_t *obj)
 fail_mdir:
 	sqfs_destroy(copy->meta_inode);
 fail_mino:
+	sqfs_dir_reader_dcache_cleanup(copy);
+fail_cache:
 	free(copy);
 	return NULL;
 }
@@ -50,22 +56,22 @@ sqfs_dir_reader_t *sqfs_dir_reader_create(const sqfs_super_t *super,
 	sqfs_dir_reader_t *rd;
 	sqfs_u64 start, limit;
 
-	if (flags != 0)
+	if (flags & ~SQFS_DIR_READER_ALL_FLAGS)
 		return NULL;
 
 	rd = calloc(1, sizeof(*rd));
 	if (rd == NULL)
 		return NULL;
 
+	if (sqfs_dir_reader_dcache_init(rd, flags))
+		goto fail_dcache;
+
 	start = super->inode_table_start;
 	limit = super->directory_table_start;
 
 	rd->meta_inode = sqfs_meta_reader_create(file, cmp, start, limit);
-
-	if (rd->meta_inode == NULL) {
-		free(rd);
-		return NULL;
-	}
+	if (rd->meta_inode == NULL)
+		goto fail_mino;
 
 	start = super->directory_table_start;
 	limit = super->id_table_start;
@@ -77,17 +83,22 @@ sqfs_dir_reader_t *sqfs_dir_reader_create(const sqfs_super_t *super,
 		limit = super->export_table_start;
 
 	rd->meta_dir = sqfs_meta_reader_create(file, cmp, start, limit);
-
-	if (rd->meta_dir == NULL) {
-		sqfs_destroy(rd->meta_inode);
-		free(rd);
-		return NULL;
-	}
+	if (rd->meta_dir == NULL)
+		goto fail_mdir;
 
 	((sqfs_object_t *)rd)->destroy = dir_reader_destroy;
 	((sqfs_object_t *)rd)->copy = dir_reader_copy;
 	rd->super = super;
+	rd->flags = flags;
+	rd->state = DIR_STATE_NONE;
 	return rd;
+fail_mdir:
+	sqfs_destroy(rd->meta_inode);
+fail_mino:
+	sqfs_dir_reader_dcache_cleanup(rd);
+fail_dcache:
+	free(rd);
+	return NULL;
 }
 
 int sqfs_dir_reader_open_dir(sqfs_dir_reader_t *rd,
@@ -96,15 +107,18 @@ int sqfs_dir_reader_open_dir(sqfs_dir_reader_t *rd,
 {
 	sqfs_u64 block_start;
 	size_t size, offset;
+	sqfs_u32 parent;
 
-	if (flags != 0)
+	if (flags & (~SQFS_DIR_OPEN_ALL_FLAGS))
 		return SQFS_ERROR_UNSUPPORTED;
 
 	if (inode->base.type == SQFS_INODE_DIR) {
+		parent = inode->data.dir.parent_inode;
 		size = inode->data.dir.size;
 		offset = inode->data.dir.offset;
 		block_start = inode->data.dir.start_block;
 	} else if (inode->base.type == SQFS_INODE_EXT_DIR) {
+		parent = inode->data.dir_ext.parent_inode;
 		size = inode->data.dir_ext.size;
 		offset = inode->data.dir_ext.offset;
 		block_start = inode->data.dir_ext.start_block;
@@ -112,6 +126,27 @@ int sqfs_dir_reader_open_dir(sqfs_dir_reader_t *rd,
 		return SQFS_ERROR_NOT_DIR;
 	}
 
+	if ((rd->flags & SQFS_DIR_READER_DOT_ENTRIES) &&
+	    !(flags & SQFS_DIR_OPEN_NO_DOT_ENTRIES)) {
+		if (sqfs_dir_reader_dcache_find(rd, inode->base.inode_number,
+						&rd->cur_ref)) {
+			return SQFS_ERROR_NO_ENTRY;
+		}
+
+		if (rd->cur_ref == rd->super->root_inode_ref) {
+			rd->parent_ref = rd->cur_ref;
+		} else if (sqfs_dir_reader_dcache_find(rd, parent,
+						       &rd->parent_ref)) {
+			return SQFS_ERROR_NO_ENTRY;
+		}
+
+		rd->state = DIR_STATE_OPENED;
+	} else {
+		rd->state = DIR_STATE_ENTRIES;
+	}
+
+	rd->start_state = rd->state;
+
 	memset(&rd->hdr, 0, sizeof(rd->hdr));
 	rd->size = size;
 	rd->entries = 0;
@@ -128,12 +163,50 @@ int sqfs_dir_reader_open_dir(sqfs_dir_reader_t *rd,
 	return sqfs_meta_reader_seek(rd->meta_dir, block_start, offset);
 }
 
+static int mk_dummy_entry(const char *str, sqfs_dir_entry_t **out)
+{
+	size_t len = strlen(str);
+	sqfs_dir_entry_t *ent;
+
+	ent = calloc(1, sizeof(sqfs_dir_entry_t) + len + 1);
+	if (ent == NULL)
+		return SQFS_ERROR_ALLOC;
+
+	ent->type = SQFS_INODE_DIR;
+	ent->size = len - 1;
+
+	strcpy((char *)ent->name, str);
+
+	*out = ent;
+	return 0;
+}
+
 int sqfs_dir_reader_read(sqfs_dir_reader_t *rd, sqfs_dir_entry_t **out)
 {
 	sqfs_dir_entry_t *ent;
 	size_t count;
 	int err;
 
+	switch (rd->state) {
+	case DIR_STATE_OPENED:
+		err = mk_dummy_entry(".", out);
+		if (err == 0)
+			rd->state = DIR_STATE_DOT;
+		return err;
+	case DIR_STATE_DOT:
+		err = mk_dummy_entry("..", out);
+		if (err == 0)
+			rd->state = DIR_STATE_DOT_DOT;
+		return err;
+	case DIR_STATE_DOT_DOT:
+		rd->state = DIR_STATE_ENTRIES;
+		break;
+	case DIR_STATE_ENTRIES:
+		break;
+	default:
+		return SQFS_ERROR_SEQUENCE;
+	}
+
 	if (!rd->entries) {
 		if (rd->size <= sizeof(rd->hdr))
 			return 1;
@@ -173,9 +246,13 @@ int sqfs_dir_reader_read(sqfs_dir_reader_t *rd, sqfs_dir_entry_t **out)
 
 int sqfs_dir_reader_rewind(sqfs_dir_reader_t *rd)
 {
+	if (rd->state == DIR_STATE_NONE)
+		return SQFS_ERROR_SEQUENCE;
+
 	memset(&rd->hdr, 0, sizeof(rd->hdr));
 	rd->size = rd->start_size;
 	rd->entries = 0;
+	rd->state = rd->start_state;
 
 	if (rd->size <= sizeof(rd->hdr))
 		return 0;
@@ -189,7 +266,10 @@ int sqfs_dir_reader_find(sqfs_dir_reader_t *rd, const char *name)
 	sqfs_dir_entry_t *ent;
 	int ret;
 
-	if (rd->size != rd->start_size) {
+	if (rd->state == DIR_STATE_NONE)
+		return SQFS_ERROR_SEQUENCE;
+
+	if (rd->size != rd->start_size || rd->state != rd->start_state) {
 		ret = sqfs_dir_reader_rewind(rd);
 		if (ret)
 			return ret;
@@ -213,12 +293,42 @@ int sqfs_dir_reader_get_inode(sqfs_dir_reader_t *rd,
 			      sqfs_inode_generic_t **inode)
 {
 	sqfs_u64 block_start;
+	sqfs_u16 offset;
+	int ret;
+
+	switch (rd->state) {
+	case DIR_STATE_DOT:
+		block_start = rd->cur_ref >> 16;
+		offset = rd->cur_ref & 0x0FFFF;
+		break;
+	case DIR_STATE_DOT_DOT:
+		block_start = rd->parent_ref >> 16;
+		offset = rd->parent_ref & 0x0FFFF;
+		break;
+	case DIR_STATE_ENTRIES:
+		block_start = rd->hdr.start_block;
+		offset = rd->inode_offset;
+		break;
+	default:
+		return SQFS_ERROR_SEQUENCE;
+	}
 
-	block_start = rd->hdr.start_block;
+	ret = sqfs_meta_reader_read_inode(rd->meta_inode, rd->super,
+					  block_start, offset, inode);
+	if (ret != 0)
+		return ret;
 
-	return sqfs_meta_reader_read_inode(rd->meta_inode, rd->super,
-					   block_start, rd->inode_offset,
-					   inode);
+	if ((*inode)->base.type == SQFS_INODE_DIR ||
+	    (*inode)->base.type == SQFS_INODE_EXT_DIR) {
+		sqfs_u32 inum = (*inode)->base.inode_number;
+		sqfs_u64 ref = (block_start << 16) | rd->inode_offset;
+
+		ret = sqfs_dir_reader_dcache_add(rd, inum, ref);
+		if (ret != 0)
+			return ret;
+	}
+
+	return 0;
 }
 
 int sqfs_dir_reader_get_root_inode(sqfs_dir_reader_t *rd,
@@ -226,7 +336,23 @@ int sqfs_dir_reader_get_root_inode(sqfs_dir_reader_t *rd,
 {
 	sqfs_u64 block_start = rd->super->root_inode_ref >> 16;
 	sqfs_u16 offset = rd->super->root_inode_ref & 0xFFFF;
+	int ret;
+
+	ret = sqfs_meta_reader_read_inode(rd->meta_inode, rd->super,
+					  block_start, offset, inode);
 
-	return sqfs_meta_reader_read_inode(rd->meta_inode, rd->super,
-					   block_start, offset, inode);
+	if (ret != 0)
+		return ret;
+
+	if ((*inode)->base.type == SQFS_INODE_DIR ||
+	    (*inode)->base.type == SQFS_INODE_EXT_DIR) {
+		sqfs_u32 inum = (*inode)->base.inode_number;
+		sqfs_u64 ref = rd->super->root_inode_ref;
+
+		ret = sqfs_dir_reader_dcache_add(rd, inum, ref);
+		if (ret != 0)
+			return ret;
+	}
+
+	return 0;
 }
diff --git a/lib/sqfs/dir_reader/internal.h b/lib/sqfs/dir_reader/internal.h
index ff162ff..cd20b69 100644
--- a/lib/sqfs/dir_reader/internal.h
+++ b/lib/sqfs/dir_reader/internal.h
@@ -17,11 +17,20 @@
 #include "sqfs/inode.h"
 #include "sqfs/error.h"
 #include "sqfs/dir.h"
+#include "rbtree.h"
 #include "util.h"
 
 #include <string.h>
 #include <stdlib.h>
 
+enum {
+	DIR_STATE_NONE = 0,
+	DIR_STATE_OPENED = 1,
+	DIR_STATE_DOT = 2,
+	DIR_STATE_DOT_DOT = 3,
+	DIR_STATE_ENTRIES = 4,
+};
+
 struct sqfs_dir_reader_t {
 	sqfs_object_t base;
 
@@ -37,6 +46,28 @@ struct sqfs_dir_reader_t {
 	size_t start_size;
 	sqfs_u16 dir_offset;
 	sqfs_u16 inode_offset;
+
+	sqfs_u32 flags;
+
+	int start_state;
+	int state;
+	sqfs_u64 parent_ref;
+	sqfs_u64 cur_ref;
+	rbtree_t dcache;
 };
 
+SQFS_INTERNAL int sqfs_dir_reader_dcache_init(sqfs_dir_reader_t *rd,
+					      sqfs_u32 flags);
+
+SQFS_INTERNAL int sqfs_dir_reader_dcache_init_copy(sqfs_dir_reader_t *copy,
+						   const sqfs_dir_reader_t *rd);
+
+SQFS_INTERNAL int sqfs_dir_reader_dcache_add(sqfs_dir_reader_t *rd,
+					     sqfs_u32 inode, sqfs_u64 ref);
+
+SQFS_INTERNAL int sqfs_dir_reader_dcache_find(sqfs_dir_reader_t *rd,
+					      sqfs_u32 inode, sqfs_u64 *ref);
+
+SQFS_INTERNAL void sqfs_dir_reader_dcache_cleanup(sqfs_dir_reader_t *rd);
+
 #endif /* DIR_READER_INTERNAL_H */
diff --git a/lib/sqfs/dir_reader/read_tree.c b/lib/sqfs/dir_reader/read_tree.c
index d173ef7..7fa944a 100644
--- a/lib/sqfs/dir_reader/read_tree.c
+++ b/lib/sqfs/dir_reader/read_tree.c
@@ -113,7 +113,8 @@ static int fill_dir(sqfs_dir_reader_t *dr, sqfs_tree_node_t *root,
 		if (n->inode->base.type == SQFS_INODE_DIR ||
 		    n->inode->base.type == SQFS_INODE_EXT_DIR) {
 			if (!(flags & SQFS_TREE_NO_RECURSE)) {
-				err = sqfs_dir_reader_open_dir(dr, n->inode, 0);
+				err = sqfs_dir_reader_open_dir(dr, n->inode,
+					       SQFS_DIR_OPEN_NO_DOT_ENTRIES);
 				if (err)
 					return err;
 
@@ -212,7 +213,8 @@ int sqfs_dir_reader_get_full_hierarchy(sqfs_dir_reader_t *rd,
 			continue;
 		}
 
-		ret = sqfs_dir_reader_open_dir(rd, tail->inode, 0);
+		ret = sqfs_dir_reader_open_dir(rd, tail->inode,
+					       SQFS_DIR_OPEN_NO_DOT_ENTRIES);
 		if (ret)
 			goto fail;
 
@@ -271,7 +273,8 @@ int sqfs_dir_reader_get_full_hierarchy(sqfs_dir_reader_t *rd,
 
 	if (tail->inode->base.type == SQFS_INODE_DIR ||
 	    tail->inode->base.type == SQFS_INODE_EXT_DIR) {
-		ret = sqfs_dir_reader_open_dir(rd, tail->inode, 0);
+		ret = sqfs_dir_reader_open_dir(rd, tail->inode,
+					       SQFS_DIR_OPEN_NO_DOT_ENTRIES);
 		if (ret)
 			goto fail;