linux-kernel - Re: [PATCH 2/2] f2fs: add sysfs entry for effective lookup mode

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Message-ID: <785306c5-27ba-4a18-b702-1d943c484a56@kernel.org>
Date: Mon, 4 Aug 2025 14:36:04 +0800
From: Chao Yu <chao@...nel.org>
To: Daniel Lee <chullee@...gle.com>, Jaegeuk Kim <jaegeuk@...nel.org>
Cc: chao@...nel.org, linux-f2fs-devel@...ts.sourceforge.net,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] f2fs: add sysfs entry for effective lookup mode

On 8/4/25 14:03, Daniel Lee wrote:
> This commit introduces a new read-only sysfs entry at
> /sys/fs/f2fs/<device>/effective_lookup_mode.
> 
> This entry displays the actual directory lookup mode F2FS is
> currently using. This is needed for debugging and verification,
> as the behavior is determined by both on-disk flags and mount
> options.
> 
> Signed-off-by: Daniel Lee <chullee@...gle.com>
> ---
>  Documentation/ABI/testing/sysfs-fs-f2fs | 14 ++++++++++++++
>  fs/f2fs/sysfs.c                         | 18 ++++++++++++++++++
>  2 files changed, 32 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-fs-f2fs b/Documentation/ABI/testing/sysfs-fs-f2fs
> index bf03263b9f46..e847a50e7403 100644
> --- a/Documentation/ABI/testing/sysfs-fs-f2fs
> +++ b/Documentation/ABI/testing/sysfs-fs-f2fs
> @@ -861,3 +861,17 @@ Description:	This is a read-only entry to show the value of sb.s_encoding_flags,
>  		SB_ENC_STRICT_MODE_FL            0x00000001
>  		SB_ENC_NO_COMPAT_FALLBACK_FL     0x00000002
>  		============================     ==========
> +
> +What:		/sys/fs/f2fs/<disk>/effective_lookup_mode
> +Date:		August 2025
> +Contact:	"Daniel Lee" <chullee@...gle.com>
> +Description:
> +		This is a read-only entry to show the effective directory lookup mode
> +		F2FS is currently using for casefolded directories.
> +		This considers both the "lookup_mode" mount option and the on-disk
> +		encoding flag, SB_ENC_NO_COMPAT_FALLBACK_FL.
> +
> +		Possible values are:
> +		- "perf": Hash-only lookup.
> +		- "compat": Hash-based lookup with a linear search fallback enabled
> +		  for casefolded directories.

Any way to know whether "perf" or "compat" comes from auto mode or not? something
like "auto:perf", "auto:compat", maybe?

Thanks,

> diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
> index 75134d69a0bd..9897dd8564e0 100644
> --- a/fs/f2fs/sysfs.c
> +++ b/fs/f2fs/sysfs.c
> @@ -281,6 +281,22 @@ static ssize_t encoding_flags_show(struct f2fs_attr *a,
>  		le16_to_cpu(F2FS_RAW_SUPER(sbi)->s_encoding_flags));
>  }
>  
> +static ssize_t effective_lookup_mode_show(struct f2fs_attr *a,
> +		struct f2fs_sb_info *sbi, char *buf)
> +{
> +	switch (f2fs_get_lookup_mode(sbi)) {
> +	case LOOKUP_PERF:
> +		return sysfs_emit(buf, "perf\n");
> +	case LOOKUP_COMPAT:
> +		return sysfs_emit(buf, "compat\n");
> +	case LOOKUP_AUTO:
> +		if (sb_no_casefold_compat_fallback(sbi->sb))
> +			return sysfs_emit(buf, "perf\n");
> +		return sysfs_emit(buf, "compat\n");
> +	}
> +	return 0;
> +}
> +
>  static ssize_t mounted_time_sec_show(struct f2fs_attr *a,
>  		struct f2fs_sb_info *sbi, char *buf)
>  {
> @@ -1166,6 +1182,7 @@ F2FS_GENERAL_RO_ATTR(current_reserved_blocks);
>  F2FS_GENERAL_RO_ATTR(unusable);
>  F2FS_GENERAL_RO_ATTR(encoding);
>  F2FS_GENERAL_RO_ATTR(encoding_flags);
> +F2FS_GENERAL_RO_ATTR(effective_lookup_mode);
>  F2FS_GENERAL_RO_ATTR(mounted_time_sec);
>  F2FS_GENERAL_RO_ATTR(main_blkaddr);
>  F2FS_GENERAL_RO_ATTR(pending_discard);
> @@ -1282,6 +1299,7 @@ static struct attribute *f2fs_attrs[] = {
>  	ATTR_LIST(current_reserved_blocks),
>  	ATTR_LIST(encoding),
>  	ATTR_LIST(encoding_flags),
> +	ATTR_LIST(effective_lookup_mode),
>  	ATTR_LIST(mounted_time_sec),
>  #ifdef CONFIG_F2FS_STAT_FS
>  	ATTR_LIST(cp_foreground_calls),