[PATCH v2] erofs: derive fsid from on-disk UUID for .statfs() if possible

[Hongzhen Luo]

Use the superblock's UUID to generate the fsid when it's non-null.

Reviewed-by: Gao Xiang <hsiangkao at linux.alibaba.com>
Reviewed-by: Jingbo Xu <jefflexu at linux.alibaba.com>
Signed-off-by: Hongzhen Luo <hongzhen at linux.alibaba.com>
---
v2: update the conversion of UUID to fsid, which looks
	cleaner.
v1: https://lore.kernel.org/all/20240409081135.6102-1-hongzhen@linux.alibaba.com/
---
 fs/erofs/super.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index c0eb139adb07..58e41dc201fc 100644
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -923,22 +923,20 @@ static int erofs_statfs(struct dentry *dentry, struct kstatfs *buf)
 {
 	struct super_block *sb = dentry->d_sb;
 	struct erofs_sb_info *sbi = EROFS_SB(sb);
-	u64 id = 0;
-
-	if (!erofs_is_fscache_mode(sb))
-		id = huge_encode_dev(sb->s_bdev->bd_dev);
 
 	buf->f_type = sb->s_magic;
 	buf->f_bsize = sb->s_blocksize;
 	buf->f_blocks = sbi->total_blocks;
 	buf->f_bfree = buf->f_bavail = 0;
-
 	buf->f_files = ULLONG_MAX;
 	buf->f_ffree = ULLONG_MAX - sbi->inos;
-
 	buf->f_namelen = EROFS_NAME_LEN;
 
-	buf->f_fsid    = u64_to_fsid(id);
+	if (uuid_is_null(&sb->s_uuid))
+		buf->f_fsid = u64_to_fsid(erofs_is_fscache_mode(sb) ? 0 :
+				huge_encode_dev(sb->s_bdev->bd_dev));
+	else
+		buf->f_fsid = uuid_to_fsid(sb->s_uuid.b);
 	return 0;
 }
 
-- 
2.37.1