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From:   Yangtao Li <frank.li@vivo.com>
To:     gregkh@linuxfoundation.org, xiang@kernel.org,
        Chao Yu <chao@kernel.org>, Yue Hu <huyue2@coolpad.com>,
        Jeffle Xu <jefflexu@linux.alibaba.com>
Cc:     damien.lemoal@opensource.wdc.com, frank.li@vivo.com,
        jth@kernel.org, linux-erofs@lists.ozlabs.org,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        naohiro.aota@wdc.com, rafael@kernel.org
Subject: Re: [PATCH 2/3] erofs: convert to use kobject_is_added()
Date:   Fri,  7 Apr 2023 15:23:03 +0800
Message-Id: <20230407072303.34570-1-frank.li@vivo.com>
In-Reply-To: <2023040602-stack-overture-d418@gregkh>
References: <2023040602-stack-overture-d418@gregkh>
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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)