[PATCH v3] erofs: add sysfs feature entry for xattr prefixes

[Jingbo Xu <jefflexu@linux.alibaba.com>]

Let /sys/fs/erofs/features/xattr_prefixes advertise that this kernel
supports the EROFS_FEATURE_INCOMPAT_XATTR_PREFIXES on-disk format.

Fixes: 6a318ccd7e08 ("erofs: enable long extended attribute name prefixes")
Cc: <stable@vger.kernel.org> # 6.4+
Reviewed-by: Gao Xiang <xiang@kernel.org>
Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
---
changes since v2:
- add Reviewed-by tag (Gao Xiang)
- update list in Documentation/ABI/testing/sysfs-fs-erofs
(https://sashiko.dev/#/patchset/20260901062243.109172-1-jefflexu%40linux.alibaba.com)
---
 Documentation/ABI/testing/sysfs-fs-erofs | 2 +-
 fs/erofs/sysfs.c                         | 2 ++
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/Documentation/ABI/testing/sysfs-fs-erofs b/Documentation/ABI/testing/sysfs-fs-erofs
index e4cf6fc6a106..0b8b4354e40b 100644
--- a/Documentation/ABI/testing/sysfs-fs-erofs
+++ b/Documentation/ABI/testing/sysfs-fs-erofs
@@ -5,7 +5,7 @@ Description:	Shows all enabled kernel features.
 		Supported features:
 		compr_cfgs, big_pcluster, chunked_file, device_table,
 		compr_head2, sb_chksum, ztailpacking, dedupe, fragments,
-		48bit, metabox.
+		xattr_prefixes, 48bit, metabox.
 
 What:		/sys/fs/erofs/<disk>/sync_decompress
 Date:		November 2021
diff --git a/fs/erofs/sysfs.c b/fs/erofs/sysfs.c
index 6734483a440f..dfcec9376cd5 100644
--- a/fs/erofs/sysfs.c
+++ b/fs/erofs/sysfs.c
@@ -95,6 +95,7 @@ EROFS_ATTR_FEATURE(sb_chksum);
 EROFS_ATTR_FEATURE(ztailpacking);
 EROFS_ATTR_FEATURE(fragments);
 EROFS_ATTR_FEATURE(dedupe);
+EROFS_ATTR_FEATURE(xattr_prefixes);
 EROFS_ATTR_FEATURE(48bit);
 EROFS_ATTR_FEATURE(metabox);
 
@@ -108,6 +109,7 @@ static struct attribute *erofs_feat_attrs[] = {
 	ATTR_LIST(ztailpacking),
 	ATTR_LIST(fragments),
 	ATTR_LIST(dedupe),
+	ATTR_LIST(xattr_prefixes),
 	ATTR_LIST(48bit),
 	ATTR_LIST(metabox),
 	NULL,
-- 
2.19.1.6.gb485710b