[PATCH -next v3] erofs: add support for FS_IOC_GETFSSYSFSPATH

[Huang Xiaojia]

FS_IOC_GETFSSYSFSPATH ioctl exposes /sys/fs path of a given filesystem,
potentially standarizing sysfs reporting. This patch add support for
FS_IOC_GETFSSYSFSPATH for erofs, "erofs/<dev>" will be outputted for bdev
cases, "erofs/[domain_id,]<fs_id>" will be outputted for fscache cases.

Signed-off-by: Huang Xiaojia <huangxiaojia2 at huawei.com>
---
v3: fix commit message, overly long line and an else branch.
For bdev, it's tested as following:
mkfs.erofs test.img <SOURCES>
mount -t erofs test.img <mntdir>
ioctl_getfssysfspath <mntdir>
erofs/<dev> will be outputted.
For fscache, it's tested via  https://github.com/lostjeffle/demand-read-cachefilesd.git
./run.sh inputdir mntdir fscachedir
ioctl_getfssysfspath mntdir
erofs/[domain_id,]<fs_id> will be outputted
v2: handle non-bdev case. https://lore.kernel.org/all/20240716112939.2355999-1-huangxiaojia2@huawei.com/
v1: https://lore.kernel.org/all/20240624063801.2476116-1-huangxiaojia2@huawei.com/
---
 fs/erofs/super.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index 1b91d9513013..d7900262aa75 100644
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -576,6 +576,21 @@ static const struct export_operations erofs_export_ops = {
 	.get_parent = erofs_get_parent,
 };
 
+static void erofs_set_sysfs_name(struct super_block *sb)
+{
+	struct erofs_sb_info *sbi = EROFS_SB(sb);
+
+	if (erofs_is_fscache_mode(sb)) {
+		if (sbi->domain_id)
+			super_set_sysfs_name_generic(sb, "%s,%s",sbi->domain_id,
+						     sbi->fsid);
+		else
+			super_set_sysfs_name_generic(sb, "%s", sbi->fsid);
+		return;
+	}
+	super_set_sysfs_name_id(sb);
+}
+
 static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
 {
 	struct inode *inode;
@@ -643,6 +658,7 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
 		sb->s_flags |= SB_POSIXACL;
 	else
 		sb->s_flags &= ~SB_POSIXACL;
+	erofs_set_sysfs_name(sb);
 
 #ifdef CONFIG_EROFS_FS_ZIP
 	xa_init(&sbi->managed_pslots);
-- 
2.34.1