linux-kernel - Re: [PATCH v3 2/5] block: Add bdev_supports

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Date:	Mon, 9 May 2016 11:23:03 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Toshi Kani <toshi.kani@....com>
Cc:	Jan Kara <jack@...e.cz>, david <david@...morbit.com>,
	Al Viro <viro@...iv.linux.org.uk>, Jens Axboe <axboe@...com>,
	Christoph Hellwig <hch@...radead.org>,
	Boaz Harrosh <boaz@...xistor.com>,
	"Theodore Ts'o" <tytso@....edu>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	Ross Zwisler <ross.zwisler@...ux.intel.com>,
	micah.parrish@....com,
	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 2/5] block: Add bdev_supports_dax() for dax mount checks

On Mon, May 9, 2016 at 11:12 AM, Toshi Kani <toshi.kani@....com> wrote:
> On Sun, 2016-05-08 at 12:14 -0700, Dan Williams wrote:
>> On Thu, May 5, 2016 at 5:29 PM, Toshi Kani <toshi.kani@....com> wrote:
>  :
>> > +int bdev_supports_dax(struct super_block *sb, int blocksize)
>> > +{
>> > +       struct blk_dax_ctl dax = {
>> > +               .sector = 0,
>> > +               .size = PAGE_SIZE,
>> > +       };
>> > +       int err;
>> > +
>> > +       if (blocksize != PAGE_SIZE) {
>> > +               vfs_msg(sb, KERN_ERR, "error: unsupported blocksize for
>> > dax");
>> > +               return -EINVAL;
>> > +       }
>> > +
>> > +       err = bdev_direct_access(sb->s_bdev, &dax);
>> > +       if (err < 0) {
>> > +               switch (err) {
>> > +               case -EOPNOTSUPP:
>> > +                       vfs_msg(sb, KERN_ERR,
>> > +                               "error: device does not support dax");
>> > +                       break;
>> > +               case -EINVAL:
>> > +                       vfs_msg(sb, KERN_ERR,
>> > +                               "error: unaligned partition for dax");
>> > +                       break;
>> > +               default:
>> > +                       vfs_msg(sb, KERN_ERR,
>> > +                               "error: dax access failed (%d)", err);
>> > +               }
>> > +               return err;
>> > +       }
>> > +
>> > +       return 0;
>> > +}
>> > +EXPORT_SYMBOL_GPL(bdev_supports_dax);
>>
>> This patch should replace blkdev_dax_capable(), or just reuse that
>> existing routine, or am I missing something?
>
> Good question.  bdev_supports_dax() is a helper function tailored for the
> filesystem's mount -o dax case.  While blkdev_dax_capable() is similar, it
> does not need error messages like "device does not support dax" since it
> implicitly enables dax when capable.  So, I think we can keep
> blkdev_dax_capable(), but change it to call bdev_direct_access() so that
> actual check is performed in a single place.

Sounds good to me.