From 03e95396153d325caa01c33d5664ef0aefe7944d Mon Sep 17 00:00:00 2001 From: Hidetoshi Seto Date: Thu, 5 Sep 2013 15:57:19 +0900 Subject: btrfs-progs: calculate available blocks on device properly 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) (According to the comment in source code, 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 beginning 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. >From further investigations I also found that this issue is easily reproduced by using -A, --alloc-start option: # truncate --size=1G testfile # ./mkfs.btrfs -A900M -f testfile : mkfs.btrfs: volumes.c:852: btrfs_alloc_chunk: Assertion `!(ret)' failed. Aborted (core dumped) In this case there is only 100MB for allocation but btrfs_alloc_chunk was going to allocate more than the 100MB. The root cause of both of above troubles is a same simple bug: btrfs_chunk_alloc does not calculate available bytes properly even though it researches how many devices have enough room to have a chunk to be allocated. So this patch introduces new function btrfs_device_avail_bytes() which returns available bytes for allocation in specified device. Signed-off-by: Hidetoshi Seto Signed-off-by: David Sterba Signed-off-by: Chris Mason --- ctree.h | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'ctree.h') diff --git a/ctree.h b/ctree.h index fedb79a..41a037c 100644 --- a/ctree.h +++ b/ctree.h @@ -814,6 +814,14 @@ struct btrfs_csum_item { u8 csum; } __attribute__ ((__packed__)); +/* + * We don't want to overwrite 1M at the beginning of device, even though + * there is our 1st superblock at 64k. Some possible reasons: + * - the first 64k blank is useful for some boot loader/manager + * - the first 1M could be scratched by buggy partitioner or somesuch + */ +#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) -- cgit v1.2.1