Re: [PATCH v4 1/7] block: Introduce blk_mq_debugfs_init()

From: Bart Van Assche <bvanassche@acm.org>
To: Luis Chamberlain <mcgrof@kernel.org>,
	Pankaj Raghav <p.raghav@samsung.com>
Cc: Jens Axboe <axboe@kernel.dk>,
	linux-block@vger.kernel.org, linux-scsi@vger.kernel.org,
	Jaegeuk Kim <jaegeuk@kernel.org>,
	Avri Altman <avri.altman@wdc.com>,
	Adrian Hunter <adrian.hunter@intel.com>,
	Christoph Hellwig <hch@lst.de>, Ming Lei <ming.lei@redhat.com>,
	Keith Busch <kbusch@kernel.org>
Subject: Re: [PATCH v4 1/7] block: Introduce blk_mq_debugfs_init()
Date: Wed, 1 Feb 2023 14:01:18 -0800	[thread overview]
Message-ID: <4c9b87dc-aeeb-43b6-0c18-4d04495683da@acm.org> (raw)
In-Reply-To: <20230201212332.p3mdb5ab3qisuo2x@garbanzo>

On 2/1/23 13:23, Luis Chamberlain wrote:
> On Wed, Feb 01, 2023 at 12:58:00PM -0800, Luis Chamberlain wrote:
>> On Mon, Jan 30, 2023 at 01:26:50PM -0800, Bart Van Assche wrote:
>>> Move the code for creating the block layer debugfs root directory into
>>> blk-mq-debugfs.c. This patch prepares for adding more debugfs
>>> initialization code by introducing the function blk_mq_debugfs_init().
>>>
>>> Cc: Christoph Hellwig <hch@lst.de>
>>> Cc: Ming Lei <ming.lei@redhat.com>
>>> Cc: Keith Busch <kbusch@kernel.org>
>>> Signed-off-by: Bart Van Assche <bvanassche@acm.org>
>>
>> Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
> 
> Sorry but actually a neuron triggered after this to remind me of commit
> 85e0cbbb8a  ("block: create the request_queue debugfs_dir on
> registration") and so using the terminology on that commit, wouldn't
> this not create now the root block debugfs dir for request-based block
> drivers?

Hi Luis,

This patch should not change any behavior with CONFIG_DEBUG_FS=y.

As one can see in include/linux/debugfs.h, debugfs_create_dir() does not 
create a directory with CONFIG_DEBUG_FS=n:

static inline struct dentry *debugfs_create_dir(const char *name,
						struct dentry *parent)
{
	return ERR_PTR(-ENODEV);
}

I think the only behavior change introduced by this patch is that 
blk_debugfs_root remains NULL with CONFIG_DEBUG_FS=n instead of being 
set to ERR_PTR(-ENODEV).

Thanks,

Bart.