Re: [PATCH v3 2/5] block: Add bdev_supports_dax() for dax mount checks

[Dan Williams]

On Thu, May 5, 2016 at 5:29 PM, Toshi Kani <toshi.kani@xxxxxxx> wrote:
> DAX imposes additional requirements to a device.  Add
> bdev_supports_dax() which performs all the precondition checks
> necessary for filesystem to mount the device with dax option.
>
> Also add a new check to verify if a partition is aligned by 4KB.
> When a partition is unaligned, any dax read/write access fails,
> except for metadata update.
>
> Signed-off-by: Toshi Kani <toshi.kani@xxxxxxx>
> Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
> Cc: Jens Axboe <axboe@xxxxxx>
> Cc: "Theodore Ts'o" <tytso@xxxxxxx>
> Cc: Andreas Dilger <adilger.kernel@xxxxxxxxx>
> Cc: Jan Kara <jack@xxxxxxx>
> Cc: Dave Chinner <david@xxxxxxxxxxxxx>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
> Cc: Boaz Harrosh <boaz@xxxxxxxxxxxxx>
> ---
>  fs/block_dev.c         |   42 ++++++++++++++++++++++++++++++++++++++++++
>  include/linux/blkdev.h |    1 +
>  2 files changed, 43 insertions(+)
>
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 7be17c4..e51a2c3 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -509,6 +509,48 @@ long bdev_direct_access(struct block_device *bdev, struct blk_dax_ctl *dax)
>  }
>  EXPORT_SYMBOL_GPL(bdev_direct_access);
>
> +/**
> + * bdev_supports_dax() - Check if the block device supports DAX
> + * @sb: The superblock of the device
> + * @blocksize: The block size of the device
> + *
> + * Return: negative errno if unsupported, 0 if supported.
> + */
> +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?