linux-kernel - Re: [PATCH 3/8] bdi: add a ->dev_name field to struct backing_dev

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Date:   Sat, 18 Apr 2020 08:40:20 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Jan Kara <jack@...e.cz>, Christoph Hellwig <hch@....de>
Cc:     axboe@...nel.dk, yuyufen@...wei.com, tj@...nel.org, tytso@....edu,
        gregkh@...uxfoundation.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/8] bdi: add a ->dev_name field to struct
 backing_dev_info

On 2020-04-17 01:59, Jan Kara wrote:
> On Thu 16-04-20 18:54:48, Christoph Hellwig wrote:
>> @@ -938,7 +938,8 @@ int bdi_register_va(struct backing_dev_info *bdi, const char *fmt, va_list args)
>>  	if (bdi->dev)	/* The driver needs to use separate queues per device */
>>  		return 0;
>>  
>> -	dev = device_create_vargs(bdi_class, NULL, MKDEV(0, 0), bdi, fmt, args);
>> +	vsnprintf(bdi->dev_name, sizeof(bdi->dev_name), fmt, args);
>> +	dev = device_create(bdi_class, NULL, MKDEV(0, 0), bdi, bdi->dev_name);
>>  	if (IS_ERR(dev))
>>  		return PTR_ERR(dev);
>>  
> 
> This can have a sideeffect not only bdi->dev_name will be truncated to 64
> chars (which generally doesn't matter) but possibly also kobject name will
> be truncated in the same way.  Which may have user visible effects. E.g.
> for fs/vboxsf 64 chars need not be enough. So shouldn't we rather do it the
> other way around - i.e., let device_create_vargs() create the device name
> and then copy to bdi->dev_name whatever fits?

How about using kvasprintf() instead of vsnprintf()?

Thanks,

Bart.