Re: [PATCH v8 3/6] libnvdimm: add dax_dev sync flag

Dan Williams
2019-05-10T20:14:24Z

On Fri, May 10, 2019 at 8:53 AM Pankaj Gupta <pagupta@redhat.com> wrote:
>
> This patch adds 'DAXDEV_SYNC' flag which is set
> for nd_region doing synchronous flush. This later
> is used to disable MAP_SYNC functionality for
> ext4 & xfs filesystem for devices don't support
> synchronous flush.
>
> Signed-off-by: Pankaj Gupta <pagupta@redhat.com>
> ---
> drivers/dax/bus.c | 2 +-
> drivers/dax/super.c | 13 ++++++++++++-
> drivers/md/dm.c | 3 ++-
> drivers/nvdimm/pmem.c | 5 ++++-
> drivers/nvdimm/region_devs.c | 7 +++++++
> include/linux/dax.h | 8 ++++++--
> include/linux/libnvdimm.h | 1 +
> 7 files changed, 33 insertions(+), 6 deletions(-)
[..]
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index 043f0761e4a0..ee007b75d9fd 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -1969,7 +1969,8 @@ static struct mapped_device *alloc_dev(int minor)
> sprintf(md->disk->disk_name, "dm-%d", minor);
>
> if (IS_ENABLED(CONFIG_DAX_DRIVER)) {
> - dax_dev = alloc_dax(md, md->disk->disk_name, &dm_dax_ops);
> + dax_dev = alloc_dax(md, md->disk->disk_name, &dm_dax_ops,
> + DAXDEV_F_SYNC);

Apologies for not realizing this until now, but this is broken.
Imaging a device-mapper configuration composed of both 'async'
virtio-pmem and 'sync' pmem. The 'sync' flag needs to be unified
across all members. I would change this argument to '0' and then
arrange for it to be set at dm_table_supports_dax() time after
validating that all components support synchronous dax.