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wangzijie 8ec4fa035c f2fs: fix zero-sized extent for precache extents 
[ Upstream commit 8175c86439 ]

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: c4020b2da4 ("f2fs: support F2FS_IOC_PRECACHE_EXTENTS")
Signed-off-by: wangzijie <wangzijie1@honor.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2025-10-15 12:00:12 +02:00
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README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.