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

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Message-ID: <20250804060327.512247-2-chullee@google.com>
Date: Sun,  3 Aug 2025 23:03:27 -0700
From: Daniel Lee <chullee@...gle.com>
To: Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <chao@...nel.org>
Cc: linux-f2fs-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org, 
	Daniel Lee <chullee@...gle.com>
Subject: [PATCH 2/2] f2fs: add sysfs entry for effective lookup mode

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.
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),
-- 
2.50.1.565.gc32cd1483b-goog