Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Yangtao Li <frank.li@vivo.com>
To:     gregkh@linuxfoundation.org
Cc:     chao@kernel.org, damien.lemoal@opensource.wdc.com,
        frank.li@vivo.com, huyue2@coolpad.com, jefflexu@linux.alibaba.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, xiang@kernel.org
Subject: Re: [PATCH 2/3] erofs: convert to use kobject_is_added()
Date:   Fri,  7 Apr 2023 14:09:00 +0800
Message-Id: <20230407060901.22446-1-frank.li@vivo.com>
In-Reply-To: <2023040602-stack-overture-d418@gregkh>
References: <2023040602-stack-overture-d418@gregkh>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?TmxZcDQyaHdUTFdMYjNnRkV5OTNJeUZNKzRCVU9RQlNIbTlpZUlzV1YyWXVr?=
 =?utf-8?B?UnBVVTRwQVRxMmtjZmFET0ttNmhibHFmUTdlM0duclowRFVCMkhDbWpDMmsr?=
 =?utf-8?B?Tlo0dnI5dUloR2JNN1h4R3RtVlk0WVV4YmZ1bjkwLzRSQzdzY25jZGlwRmkr?=
 =?utf-8?B?RDFnVGVjNGsrS29BR1Vqbi9RelZWeUF3WUZEeXEwSXpvS01veVZJaFIxUG8v?=
 =?utf-8?B?eEZRTWdNZ2dHd0J3ZlpxRFdxUTd6OTl1UXhYTy9ENjZjdktBY0ZtRVJXV3Uy?=
 =?utf-8?B?Nk1abEdmRHYyMnJTV2h1Z2JkNkowS05sVTd5WFoyRmM2eFl5OHBLYkFqeTJ6?=
 =?utf-8?B?UWJZZGk2WCtIOUlIaTdkRGlpTi94QkVtbmMwMGI2Z0VzODJzTjlwakloem1S?=
 =?utf-8?B?dFNSN2VZYkRON0ZyVlJpaTZVQ3ZUblB0VWRTYTlQTHBSZ3NiUDR5czZUbW5x?=
 =?utf-8?B?SGo3KzBpUUx5ZGdUMjVqUFk1Z2N0N25tT1A1akd6T2Q2OHFqNDVibUpPV29u?=
 =?utf-8?B?Uk1pWkE0MDBKSUg5SEdHeXoxTW5NMTV0UU5yQW10eUNBN3FuU3pBUUVPaU5F?=
 =?utf-8?B?R2xsU2xUbW1Qd2NRdTBkU1lLVWxTSEVmMG5maGsrKzVIWWF1bytZUERFSmxz?=
 =?utf-8?B?RHdPNjNxUnVtd0taT28wU3hJVThZSkIzdUhHNU9sODhWMUZSUGhpcitqTXhx?=
 =?utf-8?B?M3RDYzAzakVDMFFaYlZ2ZmNYamUyWkI0YWFSb1dMSVVueitZWW9VbDM4YXZv?=
 =?utf-8?B?UUxGYVl0cSs3a0xTMDdjQlU4SkVzUWdLTXEyMW1DemtocS9HT3lOY2Z1N01m?=
 =?utf-8?B?R0wzaGhmSXNuTi9BbVhkdFpvYUhMZ1Q2WFFRT3U5dTZLRWR3a1NmT25EZWhj?=
 =?utf-8?B?RHE5SE1YbXQyNjhuZHc2d213Q28yOVgrNFo0RWpES1BqNGRDMWtTb1JJaHJX?=
 =?utf-8?B?SmdiT2FEOGZ4SmdSaGlHK1hWRFZJakV2MkNZRmdCSmtDdlpyY3BUa0Rqcm1y?=
 =?utf-8?B?Qm4wWkZhU3l3b2pwUi9qYUxJME1Ram9QT2E5SzQ3SGhlTmpZdDc4bUNzRTNG?=
 =?utf-8?B?T0RwZDBHKzNNbjdqWVBFOURXcUpraEpCNldNU0NwdjZqL0VPa2x0YWw1bTRG?=
 =?utf-8?B?cVg3eldpTkZBMFBLMzFJZkMzZDZsWnlGMWd6cExNSkIxL2tNTVJXTk83dDhi?=
 =?utf-8?B?S1BPZ0ZHMlVnWk9QYTE3Vmc4ZXIxSnVidGQ3aFR5UTN1WXl3UU1tSW04QWJp?=
 =?utf-8?B?dUtGTmpFdkZlbzVlU2FiMmxsdGF0WXRadUNzNmM0encvTVg2RlB4Y0M3OHpi?=
 =?utf-8?B?S01pb3lLTFU3aTBYMTVSc3ExTDFHQTdJdkpHdkRzQlJ5eFJEQyt5dkU1VS9u?=
 =?utf-8?B?WUJNWmFmWEFrcFpRY0hiRHN1TUtGT2RvSHpDd3BZM3pCekU5K1FlOVVZSy9m?=
 =?utf-8?B?cU9ETmJNb1ZiM01OKzFldjdxSVhvK0NoOWNPWk5IYWlpWXQ3MVBnYXA0OTNW?=
 =?utf-8?B?N2hLUHN0eC9QZ2h1cnlLVHpUUk9OS0VSb1U0T1dJVVlzV2V2TUx3RWdCMkJW?=
 =?utf-8?B?MGc5KytCbjJlTERPY2t2NHJjVUxsQkVlNVMybERFT2EybFU1TUZ6VnErbFM0?=
 =?utf-8?B?Wm5CcDY4azBFZ3pBM1VzcHMyOE43c1ZXbVBPc003T0lINzBUcVhuMSsxdEVL?=
 =?utf-8?B?YUM1U005dXJ6K3BGQTUvSXNpZGZSSjR5M2JFUCsyL09xR2ZJRzVLMHBJUGsv?=
 =?utf-8?B?MHI5QmdYK01GaXpXUWhrbEpKU0d4Y2t6clc2TzJXSnNzb2ZKWUJTY2NwNWdz?=
 =?utf-8?B?cHMwdlI4SXVIVHpBbVV2YWNkOVNmRHZEL0djNmU2RDJUd3NkaS9CN0E4cmFF?=
 =?utf-8?B?MHFOTmEvend6TWJEbmxnZmJjb0l2cURIa3RsTVIyRmN6Mk5lVldLTHJFenI5?=
 =?utf-8?B?amdUWWhyR1BrNHFGTVNJcEJ3aVIvNjYzS005MnZFS1BEa3VUY1p5aEZEZ29J?=
 =?utf-8?B?WWZ4UUYrV1hKakQ2MHpPRGozM0xkSHNLQzNXdVJEcGl5UlF1cWE2emxCV21W?=
 =?utf-8?B?NXZENjNmeTlnTlNJaE9udTZVT25zd2kzbjhXUDlDaDIzaVJ4aGhIOGtOMUdB?=
 =?utf-8?Q?C/I6CJVRdIgo1XnXlA4jCozIg?=
X-OriginatorOrg: vivo.com
X-MS-Exchange-CrossTenant-Network-Message-Id: c4b22288-b0c3-428d-bb9b-08db372e9a17
X-MS-Exchange-CrossTenant-AuthSource: SEZPR06MB5269.apcprd06.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 07 Apr 2023 06:09:10.0107
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 923e42dc-48d5-4cbe-b582-1a797a6412ed
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: aVEbf2mKqBLfs/qRd4eJ1RId5rF6FMaAvh2c2YfABXnRoFYT0rA72zFVKKw+miTPVOKvEv9m3knkqoBDUsAJSA==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: TYUPR06MB6079
X-Spam-Status: No, score=-0.2 required=5.0 tests=DKIM_SIGNED,DKIM_VALID,
        DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H2,
        SPF_HELO_PASS,SPF_PASS autolearn=unavailable autolearn_force=no
        version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
        lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

Hi Greg,

> just let it hang off as a separate structure (i.e. a pointer to something else.)

I have made some attempts. According to my understanding, the reason why the
filesystem needs to embed the kobj structure (not a pointer) is that the kobj_to_sbi
method is required in the attr_store/attr_show method for subsequent data processing.

130 static ssize_t erofs_attr_store(struct kobject *kobj, struct attribute *attr,
131                                                 const char *buf, size_t len)
132 {
133         struct erofs_sb_info *sbi = container_of(kobj, struct erofs_sb_info,
134                                                 s_kobj);

If we turn the kobject in sbi into a pointer, then we need to insert a pointer
to sbi in the kobject, or perform the following encapsulation.

struct filesystem_kobject {
        struct kobject kobject;
	void *private;
};

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

BTW, Now sysfs.c in many file systems is full of a lot of repetitive code, maybe we can abstract the common part?
Like filesystem_attr、filesystem_kobject_ops、filesystem_kobject_ktype...

Thx,
Yangtao