linux-kernel - Re: [RFC 1/3] block: move main block debugfs initialization to its own file

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Date:   Mon, 6 Apr 2020 14:23:47 +0000
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Bart Van Assche <bvanassche@....org>
Cc:     axboe@...nel.dk, viro@...iv.linux.org.uk,
        gregkh@...uxfoundation.org, rostedt@...dmis.org, mingo@...hat.com,
        jack@...e.cz, ming.lei@...hat.com, nstange@...e.de,
        mhocko@...e.com, linux-block@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Omar Sandoval <osandov@...com>,
        Hannes Reinecke <hare@...e.com>,
        Michal Hocko <mhocko@...nel.org>
Subject: Re: [RFC 1/3] block: move main block debugfs initialization to its
 own file

On Sat, Apr 04, 2020 at 08:12:53PM -0700, Bart Van Assche wrote:
> On 2020-04-01 17:00, Luis Chamberlain wrote:
> > Single and multiqeueue block devices share some debugfs code. By
>              ^^^^^^^^^^^
>              multiqueue?
> > moving this into its own file it makes it easier to expand and audit
> > this shared code.
> 
> [ ... ]
> 
> > diff --git a/block/blk-debugfs.c b/block/blk-debugfs.c
> > new file mode 100644
> > index 000000000000..634dea4b1507
> > --- /dev/null
> > +++ b/block/blk-debugfs.c
> > @@ -0,0 +1,15 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +/*
> > + * Shared debugfs mq / non-mq functionality
> > + */
> 
> The legacy block layer is gone, so not sure why the above comment refers
> to non-mq?

Will adjust the language, thanks.

> 
> > diff --git a/block/blk.h b/block/blk.h
> > index 0a94ec68af32..86a66b614f08 100644
> > --- a/block/blk.h
> > +++ b/block/blk.h
> > @@ -487,5 +487,12 @@ struct request_queue *__blk_alloc_queue(int node_id);
> >  int __bio_add_pc_page(struct request_queue *q, struct bio *bio,
> >  		struct page *page, unsigned int len, unsigned int offset,
> >  		bool *same_page);
> > +#ifdef CONFIG_DEBUG_FS
> > +void blk_debugfs_register(void);
> > +#else
> > +static inline void blk_debugfs_register(void)
> > +{
> > +}
> > +#endif /* CONFIG_DEBUG_FS */
> 
> Do we really need a new header file that only declares a single
> function? How about adding the above into block/blk-mq-debugfs.h?

Moving forward rq->debugfs_dir will created when CONFIG_DEBUG_FS is
enabled to enable blktrace to use it. This creation won't depend on
CONFIG_BLK_DEBUG_FS, so we can definitely sprinkly the #ifdef
CONFIG_DEBUG_FS stuff in block/blk-mq-debugfs.h but it just didn't
seem the best place. Let me know.

  Luis