linux-ext4 - Re: [PATCH v5 3/6] libnvdimm: add dax

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Date:   Thu, 11 Apr 2019 07:56:36 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Pankaj Gupta <pagupta@...hat.com>
Cc:     linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org,
        KVM list <kvm@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux ACPI <linux-acpi@...r.kernel.org>,
        Qemu Developers <qemu-devel@...gnu.org>,
        linux-ext4 <linux-ext4@...r.kernel.org>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        Ross Zwisler <zwisler@...nel.org>,
        Vishal L Verma <vishal.l.verma@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Christoph Hellwig <hch@...radead.org>,
        Len Brown <lenb@...nel.org>, Jan Kara <jack@...e.cz>,
        "Theodore Ts'o" <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        lcapitulino@...hat.com, Kevin Wolf <kwolf@...hat.com>,
        Igor Mammedov <imammedo@...hat.com>,
        jmoyer <jmoyer@...hat.com>,
        Nitesh Narayan Lal <nilal@...hat.com>,
        Rik van Riel <riel@...riel.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        david <david@...morbit.com>, cohuck@...hat.com,
        Xiao Guangrong <xiaoguangrong.eric@...il.com>,
        Paolo Bonzini <pbonzini@...hat.com>, kilobyte@...band.pl,
        yuval.shaia@...cle.com
Subject: Re: [PATCH v5 3/6] libnvdimm: add dax_dev sync flag

On Tue, Apr 9, 2019 at 9:10 PM Pankaj Gupta <pagupta@...hat.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@...hat.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);