Re: [f2fs-dev] [PATCH v3 1/2] f2fs: fix zero-sized extent for precache extents

[Chao Yu <chao@kernel.org>]

On 9/17/25 10:36, wangzijie wrote:
> Script to reproduce:
> f2fs_io write 1 0 1881 rand dsync testfile
> f2fs_io fallocate 0 7708672 4096 testfile
> f2fs_io write 1 1881 1 rand buffered testfile
> fsync testfile
> umount
> mount
> f2fs_io precache_extents testfile
> 
> When the data layout is something like this:
> dnode1:                     dnode2:
> [0]      A                  [0]    NEW_ADDR
> [1]      A+1                [1]    0x0
> ...
> [1016]   A+1016
> [1017]   B (B!=A+1017)      [1017] 0x0
> 
> During precache_extents, we map the last block(valid blkaddr) in dnode1:
> map->m_flags |= F2FS_MAP_MAPPED;
> map->m_pblk = blkaddr(valid blkaddr);
> map->m_len = 1;
> then we goto next_dnode, meet the first block in dnode2(hole), goto sync_out:
> map->m_flags & F2FS_MAP_MAPPED == true, and we make zero-sized extent:
> 
> map->m_len = 1
> ofs = start_pgofs - map->m_lblk = 1882 - 1881 = 1
> ei.fofs = start_pgofs = 1882
> ei.len = map->m_len - ofs = 1 - 1 = 0
> 
> 
> Rebased on patch[1], this patch can cover these cases to avoid zero-sized extent:
> A,B,C is valid blkaddr
> case1:
> dnode1:                     dnode2:
> [0]      A                  [0]    NEW_ADDR
> [1]      A+1                [1]    0x0
> ...                         ....
> [1016]   A+1016
> [1017]   B (B!=A+1017)      [1017] 0x0
> 
> case2:
> dnode1:                     dnode2:
> [0]      A                  [0]    C (C!=B+1)
> [1]      A+1                [1]    C+1
> ...                         ....
> [1016]   A+1016
> [1017]   B (B!=A+1017)      [1017] 0x0
> 
> case3:
> dnode1:                     dnode2:
> [0]      A                  [0]    C (C!=B+2)
> [1]      A+1                [1]    C+1
> ...                         ....
> [1015]   A+1015
> [1016]   B (B!=A+1016)
> [1017]   B+1                [1017] 0x0
> 
> [1] https://lore.kernel.org/linux-f2fs-devel/20250912081250.44383-1-chao@kernel.org/
> 
> Fixes: c4020b2da4c9 ("f2fs: support F2FS_IOC_PRECACHE_EXTENTS")
> Signed-off-by: wangzijie <wangzijie1@honor.com>

Reviewed-by: Chao Yu <chao@kernel.org>

Thanks,