@@ -811,6 +811,9 @@ struct btrfs_csum_item {
u8 csum;
} __attribute__ ((__packed__));
+/* we have reserved 1M for superblock at the begging of device */
+#define BTRFS_BLOCK_RESERVED_1M_FOR_SUPER ((u64)1024 * 1024)
+
/* tag for the radix tree of block groups in ram */
#define BTRFS_BLOCK_GROUP_DATA (1ULL << 0)
#define BTRFS_BLOCK_GROUP_SYSTEM (1ULL << 1)
@@ -283,7 +283,7 @@ static int find_free_dev_extent(struct btrfs_trans_handle *trans,
/* we don't want to overwrite the superblock on the drive,
* so we make sure to start at an offset of at least 1MB
*/
- search_start = max((u64)1024 * 1024, search_start);
+ search_start = max(BTRFS_BLOCK_RESERVED_1M_FOR_SUPER, search_start);
if (root->fs_info->alloc_start + num_bytes <= device->total_bytes)
search_start = max(root->fs_info->alloc_start, search_start);
@@ -783,6 +783,11 @@ again:
while(index < num_stripes) {
device = list_entry(cur, struct btrfs_device, dev_list);
avail = device->total_bytes - device->bytes_used;
+ /* we have reserved 1M for superblock at the head of device */
+ if (avail > BTRFS_BLOCK_RESERVED_1M_FOR_SUPER)
+ avail -= BTRFS_BLOCK_RESERVED_1M_FOR_SUPER;
+ else
+ avail = 0;
cur = cur->next;
if (avail >= min_free) {
list_move_tail(&device->dev_list, &private_devs);
I found that mkfs.btrfs aborts when assigned multi volumes contain a small volume: # parted /dev/sdf p Model: LSI MegaRAID SAS RMB (scsi) Disk /dev/sdf: 72.8GB Sector size (logical/physical): 512B/512B Partition Table: msdos Number Start End Size Type File system Flags 1 32.3kB 72.4GB 72.4GB primary 2 72.4GB 72.8GB 461MB primary # ./mkfs.btrfs -f /dev/sdf1 /dev/sdf2 : SMALL VOLUME: forcing mixed metadata/data groups adding device /dev/sdf2 id 2 mkfs.btrfs: volumes.c:852: btrfs_alloc_chunk: Assertion `!(ret)' failed. Aborted (core dumped) This failure of btrfs_alloc_chunk was caused by following steps: 1) since there is only small space in the small device, mkfs was going to allocate a chunk from free space as much as available. So mkfs called btrfs_alloc_chunk with size = device->total_bytes - device->used_bytes. 2) To avoid overwriting superblock, btrfs_alloc_chunk starts taking chunks at an offset of 1MB. It means that the layout of a disk will be like: [[1MB at begging for sb][allocated chunks]* ... free space ... ] and you can see that the available free space for allocation is: avail = device->total_bytes - device->used_bytes - 1MB. 3) Therefore there is only free space 1MB less than requested. damn. So this fix let mkfs know how much spaces are really there. Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com> --- ctree.h | 3 +++ volumes.c | 7 ++++++- 2 files changed, 9 insertions(+), 1 deletions(-)