Re: [PATCH v3 4/5] ext4: disable map_sync for virtio pmem

[Jan Kara]

On Wed 09-01-19 19:26:05, Pankaj Gupta wrote:
> Virtio pmem provides asynchronous host page cache flush
> mechanism. We don't support 'MAP_SYNC' with virtio pmem 
> and ext4. 
> 
> Signed-off-by: Pankaj Gupta <pagupta@xxxxxxxxxx>
...
> @@ -371,6 +373,13 @@ static int ext4_file_mmap(struct file *file, struct vm_area_struct *vma)
>  	if (!IS_DAX(file_inode(file)) && (vma->vm_flags & VM_SYNC))
>  		return -EOPNOTSUPP;
>  
> +	/* We don't support synchronous mappings with guest direct access
> +	 * and virtio based host page cache flush mechanism.
> +	 */
> +	if (IS_DAX(file_inode(file)) && virtio_pmem_host_cache_enabled(dax_dev)
> +						&& (vma->vm_flags & VM_SYNC))
> +		return -EOPNOTSUPP;
> +

Shouldn't there rather be some generic way of doing this? Having
virtio_pmem_host_cache_enabled() check in filesystem code just looks like
filesystem sniffing into details is should not care about... Maybe just
naming this (or having a wrapper) dax_dev_map_sync_supported()?

								Honza
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR