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SubjectRe: [PATCH v3 4/5] ext4: disable map_sync for virtio pmem
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@redhat.com>
...
> @@ -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@suse.com>
SUSE Labs, CR

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