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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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