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SubjectRe: [PATCH v3 2/5] block: Add bdev_supports_dax() for dax mount checks
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On Thu, May 5, 2016 at 5:29 PM, Toshi Kani <toshi.kani@hpe.com> 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@hpe.com>
> Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> Cc: Jens Axboe <axboe@fb.com>
> Cc: "Theodore Ts'o" <tytso@mit.edu>
> Cc: Andreas Dilger <adilger.kernel@dilger.ca>
> Cc: Jan Kara <jack@suse.cz>
> Cc: Dave Chinner <david@fromorbit.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
> Cc: Christoph Hellwig <hch@infradead.org>
> Cc: Boaz Harrosh <boaz@plexistor.com>
> ---
> 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?

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