BACKPORT: FROMGIT: 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.
Bug: 432807936
(cherry picked from commit 1bd119da0b93d6d61891edf2b9d036800aba687f
https: //git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs.git dev)
Link: https://lore.kernel.org/linux-f2fs-devel/20250805065228.1473089-1-chullee@google.com/
Change-Id: Iabb9548bb9f73ef42d46ed0506a0372ec37e75d8
[chullee: resolved merge conflicts in the document]
Signed-off-by: Daniel Lee <chullee@google.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/Documentation/ABI/testing/sysfs-fs-f2fs b/Documentation/ABI/testing/sysfs-fs-f2fs
index 90f4dd4..822a2cd 100644
--- a/Documentation/ABI/testing/sysfs-fs-f2fs
+++ b/Documentation/ABI/testing/sysfs-fs-f2fs
@@ -487,3 +487,18 @@
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@google.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
+ - "auto:perf": lookup_mode is auto and fallback is disabled on-disk
+ - "auto:compat": lookup_mode is auto and fallback is enabled on-disk
diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
index 740d0a4..92a4861 100644
--- a/fs/f2fs/sysfs.c
+++ b/fs/f2fs/sysfs.c
@@ -211,6 +211,22 @@ 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, "auto:perf\n");
+ return sysfs_emit(buf, "auto:compat\n");
+ }
+ return 0;
+}
+
static ssize_t mounted_time_sec_show(struct f2fs_attr *a,
struct f2fs_sb_info *sbi, char *buf)
{
@@ -701,6 +717,7 @@ 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);
#ifdef CONFIG_F2FS_STAT_FS
@@ -809,6 +826,7 @@ 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),
