Re: [PATCH v5 4/6] dax: check synchronous mapping is supported

Jan Kara
2019-04-10T08:25:18Z

On Wed 10-04-19 09:38:24, Pankaj Gupta wrote:
> This patch introduces 'daxdev_mapping_supported' helper
> which checks if 'MAP_SYNC' is supported with filesystem
> mapping. It also checks if corresponding dax_device is
> synchronous. Virtio pmem device is asynchronous and
> does not not support VM_SYNC.
>
> Suggested-by: Jan Kara <jack@suse.cz>
> Signed-off-by: Pankaj Gupta <pagupta@redhat.com>
> ---
> include/linux/dax.h | 23 +++++++++++++++++++++++
> 1 file changed, 23 insertions(+)
>
> diff --git a/include/linux/dax.h b/include/linux/dax.h
> index b896706a5ee9..4a2a60ffec86 100644
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -38,6 +38,24 @@ void kill_dax(struct dax_device *dax_dev);
> void dax_write_cache(struct dax_device *dax_dev, bool wc);
> bool dax_write_cache_enabled(struct dax_device *dax_dev);
> bool dax_synchronous(struct dax_device *dax_dev);
> +
> +/*
> + * Callers check if synchronous mapping is enabled for DAX file
> + * and attached dax device is also synchronous.
> + *
> + * dax_synchronous function verifies if dax device is synchronous.
> + * Currently, only virtio pmem device supports asynchronous device
> + * flush.
> + */

Thanks for the patch! I'd restructure this comment like:

/*
* Check if given mapping is supported by the file / underlying device.
*/
> +static inline bool daxdev_mapping_supported(struct vm_area_struct *vma,
> + struct dax_device *dax_dev)
> +{

/* Everyone supports non-sync mappings */
> + if (!(vma->vm_flags & VM_SYNC))
> + return true;
/* Sync mappings are supported only for files using DAX */
> + if (!IS_DAX(file_inode(vma->vm_file)))
> + return false;
/* Underlying device must support persisting through CPU instructions */
> + return dax_synchronous(dax_dev);
> +}
> #else
> static inline struct dax_device *dax_get_by_host(const char *host)
> {
> @@ -69,6 +87,11 @@ static inline bool dax_synchronous(struct dax_device *dax_dev)
> {
> return true;
> }
> +static inline bool daxdev_mapping_supported(struct vm_area_struct *vma,
> + struct dax_device *dax_dev)
> +{
> + return true;

This looks wrong. Shouldn't it rather be:

return !(vma->flags & VM_SYNC);

?

Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR