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SubjectRe: [PATCH v3 13/15] block, dax: make dax mappings opt-in by default
On Sun, Nov 01, 2015 at 11:30:53PM -0500, Dan Williams wrote:
> Now that we have the ability to dynamically enable DAX for a raw block
> inode, make the behavior opt-in by default. DAX does not have feature
> parity with pagecache backed mappings, so applications should knowingly
> enable DAX semantics.
>
> Note, this is only for mappings returned to userspace. For the
> synchronous usages of DAX, dax_do_io(), there is no semantic difference
> with the bio submission path, so that path remains default enabled.
>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
> block/ioctl.c | 3 +--
> fs/block_dev.c | 33 +++++++++++++++++++++++----------
> include/linux/fs.h | 8 ++++++++
> 3 files changed, 32 insertions(+), 12 deletions(-)
>
> diff --git a/block/ioctl.c b/block/ioctl.c
> index 205d57612fbd..c4c3a09d9ca9 100644
> --- a/block/ioctl.c
> +++ b/block/ioctl.c
> @@ -298,13 +298,12 @@ static inline int is_unrecognized_ioctl(int ret)
> #ifdef CONFIG_FS_DAX
> static int blkdev_set_dax(struct block_device *bdev, int n)
> {
> - struct gendisk *disk = bdev->bd_disk;
> int rc = 0;
>
> if (n)
> n = S_DAX;
>
> - if (n && !disk->fops->direct_access)
> + if (n && !blkdev_dax_capable(bdev))
> return -ENOTTY;
>
> mutex_lock(&bdev->bd_inode->i_mutex);
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 13ce6d0ff7f6..ee34a31e6fa4 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -152,16 +152,37 @@ static struct inode *bdev_file_inode(struct file *file)
> return file->f_mapping->host;
> }
>
> +#ifdef CONFIG_FS_DAX
> +bool blkdev_dax_capable(struct block_device *bdev)
> +{
> + struct gendisk *disk = bdev->bd_disk;
> +
> + if (!disk->fops->direct_access)
> + return false;
> +
> + /*
> + * If the partition is not aligned on a page boundary, we can't
> + * do dax I/O to it.
> + */
> + if ((bdev->bd_part->start_sect % (PAGE_SIZE / 512))
> + || (bdev->bd_part->nr_sects % (PAGE_SIZE / 512)))
> + return false;
> +
> + return true;

Where do you check that S_DAX has been enabled on the block device
now?

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com


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