Unsquash-4: update to dynamically read directory table

Originally when Unsquashfs was written it decompressed
the entire filesystem, and wrote it out to disk.
As such it made sense to read and decompress the
entire directory table at start-up.

Since then new options have been added to Unsquashfs which
can significantly limit the amount of the filesystem
written to disk, e.g. extract files, and more recently
exclude files and depth limiting (-max option).

So it no longer makes sense to read and decompress
the entire directory table at start-up, when much of it
may never be referenced.  It just adds unnecessary
overhead.

Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>

Author: plougher

squashfs-tools/unsquash-4.c

@@ -29,7 +29,6 @@
 
 static struct squashfs_fragment_entry *fragment_table;
 static unsigned int *id_table;
-static char *directory_table;
 static squashfs_operations ops;
 
 static void read_block_list(unsigned int *block_list, long long start,
@@ -330,8 +329,7 @@ static struct dir *squashfs_opendir(unsigned int block_start, unsigned int offse
 		__attribute__((aligned));
 	struct squashfs_dir_entry *dire = (struct squashfs_dir_entry *) buffer;
 	long long start;
-	long long bytes;
-	int dir_count, size;
+	int bytes = 0, dir_count, size, res;
 	struct dir_ent *new_dir;
 	struct dir *dir;
 
@@ -363,17 +361,15 @@ static struct dir *squashfs_opendir(unsigned int block_start, unsigned int offse
 		return dir;
 
 	start = sBlk.s.directory_table_start + (*i)->start;
-	bytes = lookup_entry(directory_table_hash, start);
-
-	if(bytes == -1)
-		EXIT_UNSQUASH("squashfs_opendir: directory block %lld not "
-			"found!\n", start);
-
-	bytes += (*i)->offset;
+	offset = (*i)->offset;
 	size = (*i)->data + bytes - 3;
 
 	while(bytes < size) {			
-		SQUASHFS_SWAP_DIR_HEADER(directory_table + bytes, &dirh);
+		res = read_directory_data(&dirh, &start, &offset, sizeof(dirh));
+		if(res == FALSE)
+			goto corrupted;
+
+		SQUASHFS_INSWAP_DIR_HEADER(&dirh);
 
 		dir_count = dirh.count + 1;
 		TRACE("squashfs_opendir: Read directory header @ byte position "
@@ -387,7 +383,11 @@ static struct dir *squashfs_opendir(unsigned int block_start, unsigned int offse
 		}
 
 		while(dir_count--) {
-			SQUASHFS_SWAP_DIR_ENTRY(directory_table + bytes, dire);
+			res = read_directory_data(dire, &start, &offset, sizeof(*dire));
+			if(res == FALSE)
+				goto corrupted;
+
+			SQUASHFS_INSWAP_DIR_ENTRY(dire);
 
 			bytes += sizeof(*dire);
 
@@ -397,8 +397,11 @@ static struct dir *squashfs_opendir(unsigned int block_start, unsigned int offse
 				goto corrupted;
 			}
 
-			memcpy(dire->name, directory_table + bytes,
-				dire->size + 1);
+			res = read_directory_data(dire->name, &start, &offset,
+								dire->size + 1);
+			if(res == FALSE)
+				goto corrupted;
+
 			dire->name[dire->size + 1] = '\0';
 
 			/* check name for invalid characters (i.e /, ., ..) */
@@ -410,13 +413,15 @@ static struct dir *squashfs_opendir(unsigned int block_start, unsigned int offse
 			TRACE("squashfs_opendir: directory entry %s, inode "
 				"%d:%d, type %d\n", dire->name,
 				dirh.start_block, dire->offset, dire->type);
+
 			if((dir->dir_count % DIR_ENT_SIZE) == 0) {
 				new_dir = realloc(dir->dirs, (dir->dir_count +
 					DIR_ENT_SIZE) * sizeof(struct dir_ent));
 				if(new_dir == NULL)
 					MEM_ERROR();
 				dir->dirs = new_dir;
 			}
+
 			strcpy(dir->dirs[dir->dir_count].name, dire->name);
 			dir->dirs[dir->dir_count].start_block =
 				dirh.start_block;
@@ -633,19 +638,12 @@ static int read_filesystem_tables()
 		}
 	}
 
-	/* Read directory table */
-
-	/* Sanity check super block contents */
+	/* Sanity check super block directory table values */
 	if(sBlk.s.directory_table_start > table_start) {
 		ERROR("read_filesystem_tables: directory table start too large in super block\n");
 		goto corrupted;
 	}
 
-	directory_table = read_directory_table(sBlk.s.directory_table_start,
-				table_start);
-	if(directory_table == NULL)
-		goto corrupted;
-
 	/* Sanity check super block inode table values */
 	if(sBlk.s.inode_table_start >= sBlk.s.directory_table_start) {
 		ERROR("read_filesystem_tables: inode table start too large in super block\n");