linux-kernel - Re: [PATCH 10/12] bdi: replace BDI_CAP_STABLE

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Date:   Sat, 19 Sep 2020 08:51:26 +0200
From:   Christoph Hellwig <hch@....de>
To:     Jan Kara <jack@...e.cz>
Cc:     Christoph Hellwig <hch@....de>, Jens Axboe <axboe@...nel.dk>,
        Song Liu <song@...nel.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Richard Weinberger <richard@....at>,
        Minchan Kim <minchan@...nel.org>,
        linux-mtd@...ts.infradead.org, dm-devel@...hat.com,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        drbd-dev@...ts.linbit.com, linux-raid@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        cgroups@...r.kernel.org
Subject: Re: [PATCH 10/12] bdi: replace BDI_CAP_STABLE_WRITES with a queue
 and a sb flag

On Thu, Sep 17, 2020 at 11:25:24AM +0200, Jan Kara wrote:
> On Thu 10-09-20 16:48:30, Christoph Hellwig wrote:
> > The BDI_CAP_STABLE_WRITES is one of the few bits of information in the
> > backing_dev_info shared between the block drivers and the writeback code.
> > To help untangling the dependency replace it with a queue flag and a
> > superblock flag derived from it.  This also helps with the case of e.g.
> > a file system requiring stable writes due to its own checksumming, but
> > not forcing it on other users of the block device like the swap code.
> > 
> > One downside is that we can't support the stable_pages_required bdi
> > attribute in sysfs anymore.  It is replaced with a queue attribute, that
> > can also be made writable for easier testing.
>   ^^^^^^^^^^^^^^^^
>   is also made
> 
> For a while I was confused thinking that the new attribute is not writeable
> but when I checked the code I saw that it is.
> 
> Not supporting stable_pages_required attribute is not nice but probably it
> isn't widely used. Maybe the deprecation message can even mention to use
> the queue attribute? Otherwise the patch looks good to me so feel free to
> add:
> 
> Reviewed-by: Jan Kara <jack@...e.cz>

Thanks.  I've fixed the commit log and changed the warning to:

	dev_warn_once(dev, 
                 "the stable_pages_required attribute has been removed. Use the
		 stable_writes queue attribute instead.\n");