Re: [PATCH v5 3/6] libnvdimm: add dax_dev sync flag

[Dan Williams <dan.j.williams@intel.com>]

On Tue, Apr 9, 2019 at 9:10 PM 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              |  2 +-
>  drivers/nvdimm/pmem.c        |  3 ++-
>  drivers/nvdimm/region_devs.c |  7 +++++++
>  include/linux/dax.h          |  9 +++++++--
>  include/linux/libnvdimm.h    |  1 +
>  7 files changed, 31 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
> index 2109cfe80219..431bf7d2a7f9 100644
> --- a/drivers/dax/bus.c
> +++ b/drivers/dax/bus.c
> @@ -388,7 +388,7 @@ struct dev_dax *__devm_create_dev_dax(struct dax_region *dax_region, int id,
>          * No 'host' or dax_operations since there is no access to this
>          * device outside of mmap of the resulting character device.
>          */
> -       dax_dev = alloc_dax(dev_dax, NULL, NULL);
> +       dax_dev = alloc_dax(dev_dax, NULL, NULL, true);

I find apis that take a boolean as unreadable. What does 'true' mean?
It wastes time to go look at the function definition vs something
like:

    alloc_dax(dev_dax, NULL, NULL, DAXDEV_F_SYNC);