Re: [PATCH] f2fs: expose resizable_tail feature via sysfs

[Daeho Jeong]

+ cc: zhengdaniel@xxxxxxxxxx

On Wed, Oct 14, 2026 at 8:21 AM Daeho Jeong <daeho43@xxxxxxxxx> wrote:
>
> From: Daeho Jeong <daehojeong@xxxxxxxxxx>
>
> Userspace has no way to know whether the kernel supports the
> resizable_tail_secno mount option before mounting. Passing it to a
> kernel without the support fails the mount with -EINVAL, and checking
> /sys/fs/f2fs/<disk>/pinned_area_max_secno requires an f2fs instance
> to be mounted already.
>
> Export /sys/fs/f2fs/features/resizable_tail so that userspace can check
> the support before formatting or mounting a filesystem that relies on
> resizable_tail_secno, e.g. a filesystem whose tail is going to be shrunk
> online later.
>
> Fixes: c966d29e01bb ("f2fs: support resizable tail section and unify pinned allocation")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Daeho Jeong <daehojeong@xxxxxxxxxx>
> ---
>  Documentation/ABI/testing/sysfs-fs-f2fs | 2 +-
>  fs/f2fs/sysfs.c                         | 2 ++
>  2 files changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/ABI/testing/sysfs-fs-f2fs b/Documentation/ABI/testing/sysfs-fs-f2fs
> index c4746c416ac..8df18b5d479 100644
> --- a/Documentation/ABI/testing/sysfs-fs-f2fs
> +++ b/Documentation/ABI/testing/sysfs-fs-f2fs
> @@ -271,7 +271,7 @@ Description:        Shows all enabled kernel features.
>                 inode_crtime, lost_found, verity, sb_checksum,
>                 casefold, readonly, compression, test_dummy_encryption_v2,
>                 atomic_write, pin_file, encrypted_casefold, linear_lookup,
> -               fserror.
> +               fserror, resizable_tail.
>
>  What:          /sys/fs/f2fs/<disk>/inject_rate
>  Date:          May 2016
> diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
> index 9749da70089..8b844a8b0bf 100644
> --- a/fs/f2fs/sysfs.c
> +++ b/fs/f2fs/sysfs.c
> @@ -1421,6 +1421,7 @@ F2FS_FEATURE_RO_ATTR(linear_lookup);
>  #endif
>  F2FS_FEATURE_RO_ATTR(packed_ssa);
>  F2FS_FEATURE_RO_ATTR(fserror);
> +F2FS_FEATURE_RO_ATTR(resizable_tail);
>
>  #define ATTR_LIST(name) (&f2fs_attr_##name.attr)
>  static struct attribute *f2fs_attrs[] = {
> @@ -1592,6 +1593,7 @@ static struct attribute *f2fs_feat_attrs[] = {
>  #endif
>         BASE_ATTR_LIST(packed_ssa),
>         BASE_ATTR_LIST(fserror),
> +       BASE_ATTR_LIST(resizable_tail),
>         NULL,
>  };
>  ATTRIBUTE_GROUPS(f2fs_feat);
> --
> 2.56.0.385.gd3acb90ef8-goog
>