blob: a3ddf97825f0f8a646d22c8d980fa6d59f49a0e9 [file] [log] [blame]
* volume_id - reads filesystem label and uuid
* Copyright (C) 2004 Kay Sievers <>
* Copyright (C) 2009 Vladimir Dronnikov <>
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* Lesser General Public License for more details.
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
//config: bool "btrfs filesystem"
//config: default y
//config: depends on VOLUMEID
//kbuild:lib-$(CONFIG_FEATURE_VOLUMEID_BTRFS) += btrfs.o
#include "volume_id_internal.h"
#define BTRFS_UUID_SIZE 16
#define BTRFS_LABEL_SIZE 256
#define BTRFS_CSUM_SIZE 32
#define BTRFS_FSID_SIZE 16
#define BTRFS_MAGIC "_BHRfS_M"
struct btrfs_dev_item {
uint64_t devid;
uint64_t total_bytes;
uint64_t bytes_used;
uint32_t io_align;
uint32_t io_width;
uint32_t sector_size;
uint64_t type;
uint64_t generation;
uint64_t start_offset;
uint32_t dev_group;
uint8_t seek_speed;
uint8_t bandwidth;
uint8_t uuid[BTRFS_UUID_SIZE];
uint8_t fsid[BTRFS_UUID_SIZE];
struct btrfs_super_block {
uint8_t csum[BTRFS_CSUM_SIZE];
uint8_t fsid[BTRFS_FSID_SIZE]; // UUID
uint64_t bytenr;
uint64_t flags;
uint8_t magic[8];
uint64_t generation;
uint64_t root;
uint64_t chunk_root;
uint64_t log_root;
uint64_t log_root_transid;
uint64_t total_bytes;
uint64_t bytes_used;
uint64_t root_dir_objectid;
uint64_t num_devices;
uint32_t sectorsize;
uint32_t nodesize;
uint32_t leafsize;
uint32_t stripesize;
uint32_t sys_chunk_array_size;
uint64_t chunk_root_generation;
uint64_t compat_flags;
uint64_t compat_ro_flags;
uint64_t incompat_flags;
uint16_t csum_type;
uint8_t root_level;
uint8_t chunk_root_level;
uint8_t log_root_level;
struct btrfs_dev_item dev_item;
uint8_t label[BTRFS_LABEL_SIZE]; // LABEL
// ...
int FAST_FUNC volume_id_probe_btrfs(struct volume_id *id /*,uint64_t off*/)
// btrfs has superblocks at 64K, 64M and 256G
// minimum btrfs size is 256M
// so we never step out the device if we analyze
// the first and the second superblocks
struct btrfs_super_block *sb;
unsigned off = 64;
while (off < 64*1024*1024) {
off *= 1024;
dbg("btrfs: probing at offset 0x%x", off);
sb = volume_id_get_buffer(id, off, sizeof(*sb));
if (sb == NULL)
return -1;
if (memcmp(sb->magic, BTRFS_MAGIC, 8) != 0)
return -1;
// N.B.: btrfs natively supports 256 (>VOLUME_ID_LABEL_SIZE) size labels
volume_id_set_label_string(id, sb->label, VOLUME_ID_LABEL_SIZE);
volume_id_set_uuid(id, sb->fsid, UUID_DCE);
IF_FEATURE_BLKID_TYPE(id->type = "btrfs";)
return 0;