Re: [PATCH 10/12] bdi: replace BDI_CAP_STABLE_WRITES with a queue and a sb flag

Christoph Hellwig
2020-09-19T06:51:34Z

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@suse.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");