linux-kernel - Re: [PATCH v2] bcachefs: chardev: make bch_chardev

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Message-ID: <fa1e422c-17bd-4dff-abbd-660e15d87256@huawei.com>
Date: Fri, 12 Apr 2024 10:31:17 +0800
From: Hongbo Li <lihongbo22@...wei.com>
To: "Ricardo B. Marliere" <ricardo@...liere.net>, Kent Overstreet
	<kent.overstreet@...ux.dev>, Brian Foster <bfoster@...hat.com>
CC: <linux-bcachefs@...r.kernel.org>, <linux-kernel@...r.kernel.org>, Greg
 Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v2] bcachefs: chardev: make bch_chardev_class constant

On 2024/3/11 9:41, Hongbo Li wrote:
> It's fine for me.
> 
> On 2024/3/8 20:12, Ricardo B. Marliere wrote:
>> Since commit 43a7206b0963 ("driver core: class: make class_register() 
>> take
>> a const *"), the driver core allows for struct class to be in read-only
>> memory, so move the bch_chardev_class structure to be declared at build
>> time placing it into read-only memory, instead of having to be 
>> dynamically
>> allocated at boot time. Also, correctly clean up after failing paths in
>> bch2_chardev_init().
>>
>> Cc: Hongbo Li <lihongbo22@...wei.com>
>> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>> Suggested-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>> Signed-off-by: Ricardo B. Marliere <ricardo@...liere.net>
>> ---
>> Changes in v2:
>> - Used "free the last thing" pattern in bch2_chardev_init().
>> - Link to v1: 
>> https://lore.kernel.org/r/20240305-bcachefs-v1-1-436196e25729@marliere.net
>> ---
>>   fs/bcachefs/chardev.c | 35 ++++++++++++++++++++++-------------
>>   1 file changed, 22 insertions(+), 13 deletions(-)
>>
>> diff --git a/fs/bcachefs/chardev.c b/fs/bcachefs/chardev.c
>> index 226b39c17667..dc09f547dae6 100644
>> --- a/fs/bcachefs/chardev.c
>> +++ b/fs/bcachefs/chardev.c
>> @@ -940,7 +940,9 @@ static const struct file_operations 
>> bch_chardev_fops = {
>>   };
>>   static int bch_chardev_major;
>> -static struct class *bch_chardev_class;
>> +static const struct class bch_chardev_class = {
>> +    .name = "bcachefs",
>> +};
>>   static struct device *bch_chardev;
>>   void bch2_fs_chardev_exit(struct bch_fs *c)
>> @@ -957,7 +959,7 @@ int bch2_fs_chardev_init(struct bch_fs *c)
>>       if (c->minor < 0)
>>           return c->minor;
>> -    c->chardev = device_create(bch_chardev_class, NULL,
>> +    c->chardev = device_create(&bch_chardev_class, NULL,
>>                      MKDEV(bch_chardev_major, c->minor), c,
>>                      "bcachefs%u-ctl", c->minor);
>>       if (IS_ERR(c->chardev))
>> @@ -968,32 +970,39 @@ int bch2_fs_chardev_init(struct bch_fs *c)
>>   void bch2_chardev_exit(void)
>>   {
>> -    if (!IS_ERR_OR_NULL(bch_chardev_class))
>> -        device_destroy(bch_chardev_class,
>> -                   MKDEV(bch_chardev_major, U8_MAX));
>> -    if (!IS_ERR_OR_NULL(bch_chardev_class))
>> -        class_destroy(bch_chardev_class);
>> +    device_destroy(&bch_chardev_class, MKDEV(bch_chardev_major, 
>> U8_MAX));
>> +    class_unregister(&bch_chardev_class);
>>       if (bch_chardev_major > 0)
>>           unregister_chrdev(bch_chardev_major, "bcachefs");
>>   }
>>   int __init bch2_chardev_init(void)
>>   {
>> +    int ret;
>> +
>>       bch_chardev_major = register_chrdev(0, "bcachefs-ctl", 
>> &bch_chardev_fops);
>>       if (bch_chardev_major < 0)
>>           return bch_chardev_major;
>> -    bch_chardev_class = class_create("bcachefs");
>> -    if (IS_ERR(bch_chardev_class))
>> -        return PTR_ERR(bch_chardev_class);
>> +    ret = class_register(&bch_chardev_class);
>> +    if (ret)
>> +        goto major_out;
>> -    bch_chardev = device_create(bch_chardev_class, NULL,
>> +    bch_chardev = device_create(&bch_chardev_class, NULL,
>>                       MKDEV(bch_chardev_major, U8_MAX),
>>                       NULL, "bcachefs-ctl");
>> -    if (IS_ERR(bch_chardev))
>> -        return PTR_ERR(bch_chardev);
>> +    if (IS_ERR(bch_chardev)) {
>> +        ret = PTR_ERR(bch_chardev);
>> +        goto class_out;
>> +    }
>>       return 0;
>> +
>> +class_out:
>> +    class_unregister(&bch_chardev_class);
>> +major_out:
>> +    unregister_chrdev(bch_chardev_major, "bcachefs-ctl");
>> +    return ret;
>>   }
>>   #endif /* NO_BCACHEFS_CHARDEV */
>>
>> ---
>> base-commit: 90d35da658da8cff0d4ecbb5113f5fac9d00eb72
>> change-id: 20240305-bcachefs-27a4bb8b9f4f
>>
>> Best regards,
> 

This is a useful patch, and also works on latest code. Maybe we almost 
forgot it.

Reviewed-by: Hongbo Li <lihongbo22@...wei.com>