Hi all,

> Later, I thought I could send some demo code that strips the kobject in sbi 
> into a pointer.

I made the following modifications, not sure if I'm going the right way.

diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
index 1db018f8c2e8..8e1799f690c0 100644
--- a/fs/erofs/internal.h
+++ b/fs/erofs/internal.h
@@ -165,8 +165,7 @@ struct erofs_sb_info {
        u32 feature_incompat;
 
        /* sysfs support */
-       struct kobject s_kobj;          /* /sys/fs/erofs/<devname> */
-       struct completion s_kobj_unregister;
+       struct filesystem_kobject *f_kobj;
 
        /* fscache support */
        struct fscache_volume *volume;
diff --git a/fs/erofs/sysfs.c b/fs/erofs/sysfs.c
index 435e515c0792..70e915906012 100644
--- a/fs/erofs/sysfs.c
+++ b/fs/erofs/sysfs.c
@@ -8,6 +8,33 @@
 
 #include "internal.h"
 
+//maybe we should add following thins to include/linux/filesystem_kobject.h ?
+struct filesystem_kobject {
+       struct kobject kobject;
+       void *private;
+};
+
+void filesystem_kobject_put(struct filesystem_kobject *f_kobj)
+{
+       if (f_kobj)
+               kobject_put(&f_kobj->kobject);
+}
+
+void filesystem_kobject_set_private(struct filesystem_kobject *f_kobj, void *p)
+{
+       f_kobj->private = p;
+}
+
+void *filesystem_kobject_get_private(struct filesystem_kobject *f_kobj)
+{
+       return f_kobj->private;
+}
+
+struct kobject *filesystem_kobject_get_kobject(struct filesystem_kobject 
*f_kobj)
+{
+       return &f_kobj->kobject;
+}
+
 enum {
        attr_feature,
        attr_pointer_ui,
@@ -107,8 +134,9 @@ static unsigned char *__struct_ptr(struct erofs_sb_info 
*sbi,
 static ssize_t erofs_attr_show(struct kobject *kobj,
                                struct attribute *attr, char *buf)
 {
-       struct erofs_sb_info *sbi = container_of(kobj, struct erofs_sb_info,
-                                               s_kobj);
+       struct filesystem_kobject *f_kobject = container_of(kobj, struct 
filesystem_kobject,
+                                               kobject);
+       struct erofs_sb_info *sbi = filesystem_kobject_get_private(f_kobject);
        struct erofs_attr *a = container_of(attr, struct erofs_attr, attr);
        unsigned char *ptr = __struct_ptr(sbi, a->struct_type, a->offset);
 
@@ -130,8 +158,9 @@ static ssize_t erofs_attr_show(struct kobject *kobj,
 static ssize_t erofs_attr_store(struct kobject *kobj, struct attribute *attr,
                                                const char *buf, size_t len)
 {
-       struct erofs_sb_info *sbi = container_of(kobj, struct erofs_sb_info,
-                                               s_kobj);
+       struct filesystem_kobject *f_kobject = container_of(kobj, struct 
filesystem_kobject,
+                                               kobject);
+       struct erofs_sb_info *sbi = filesystem_kobject_get_private(f_kobject);
        struct erofs_attr *a = container_of(attr, struct erofs_attr, attr);
        unsigned char *ptr = __struct_ptr(sbi, a->struct_type, a->offset);
        unsigned long t;
@@ -169,9 +198,12 @@ static ssize_t erofs_attr_store(struct kobject *kobj, 
struct attribute *attr,
 
 static void erofs_sb_release(struct kobject *kobj)
 {
-       struct erofs_sb_info *sbi = container_of(kobj, struct erofs_sb_info,
-                                                s_kobj);
-       complete(&sbi->s_kobj_unregister);
+       struct filesystem_kobject *f_kobject = container_of(kobj, struct 
filesystem_kobject,
+                                               kobject);
+       struct erofs_sb_info *sbi = filesystem_kobject_get_private(f_kobject);
+
+       kfree(f_kobject);
+       sbi->f_kobj = NULL;
 }
 
 static const struct sysfs_ops erofs_attr_ops = {
@@ -205,6 +237,7 @@ static struct kobject erofs_feat = {
 int erofs_register_sysfs(struct super_block *sb)
 {
        struct erofs_sb_info *sbi = EROFS_SB(sb);
+       struct kobject *kobj;
        char *name;
        char *str = NULL;
        int err;
@@ -222,17 +255,24 @@ int erofs_register_sysfs(struct super_block *sb)
        } else {
                name = sb->s_id;
        }
-       sbi->s_kobj.kset = &erofs_root;
-       init_completion(&sbi->s_kobj_unregister);
-       err = kobject_init_and_add(&sbi->s_kobj, &erofs_sb_ktype, NULL, "%s", 
name);
+
+       sbi->f_kobj = kzalloc(sizeof(struct filesystem_kobject), GFP_KERNEL);
+       if (!sbi->f_kobj) {
+               kfree(str);
+               return -ENOMEM;
+       }
+       filesystem_kobject_set_private(sbi->f_kobj, sbi);
+       kobj = filesystem_kobject_get_kobject(sbi->f_kobj);
+       kobj->kset = &erofs_root;
+
+       err = kobject_init_and_add(&sbi->f_kobj->kobject, &erofs_sb_ktype, 
NULL, "%s", name);
        kfree(str);
        if (err)
                goto put_sb_kobj;
        return 0;
 
 put_sb_kobj:
-       kobject_put(&sbi->s_kobj);
-       wait_for_completion(&sbi->s_kobj_unregister);
+       filesystem_kobject_put(sbi->f_kobj);
        return err;
 }
 
@@ -240,11 +280,7 @@ void erofs_unregister_sysfs(struct super_block *sb)
 {
        struct erofs_sb_info *sbi = EROFS_SB(sb);
 
-       if (sbi->s_kobj.state_in_sysfs) {
-               kobject_del(&sbi->s_kobj);
-               kobject_put(&sbi->s_kobj);
-               wait_for_completion(&sbi->s_kobj_unregister);
-       }
+       filesystem_kobject_put(sbi->f_kobj);
 }
 
 int __init erofs_init_sysfs(void)

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