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From:   Dan Williams <dan.j.williams@intel.com>
Date:   Fri, 31 Jul 2020 07:52:36 -0700
Message-ID: <CAPcyv4iueciTchM+tkhHZd6PhmbgKhQuBWaxm2Ff2bvvZWBBOw@mail.gmail.com>
Subject: Re: [PATCH v1 2/4] device-dax: Add an 'align' attribute
To:     Joao Martins <joao.m.martins@oracle.com>
Cc:     linux-nvdimm <linux-nvdimm@lists.01.org>,
        Vishal Verma <vishal.l.verma@intel.com>,
        Dave Jiang <dave.jiang@intel.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux MM <linux-mm@kvack.org>
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On Thu, Jul 16, 2020 at 10:31 AM Joao Martins <joao.m.martins@oracle.com> wrote:
>
> Introduce a device align attribute. While doing so,
> rename the region align attribute to be more explicitly
> named as so, but keep it named as @align to retain the API
> for tools like daxctl.
>
> Changes on align may not always be valid, when say certain
> mappings were created with 2M and then we switch to 1G. So, we
> validate all ranges against the new value being attempted,
> post resizing.
>
> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
> ---
>  drivers/dax/bus.c | 101 +++++++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 92 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
> index 2578651c596e..eb384dd6a376 100644
> --- a/drivers/dax/bus.c
> +++ b/drivers/dax/bus.c
> @@ -230,14 +230,15 @@ static ssize_t region_size_show(struct device *dev,
>  static struct device_attribute dev_attr_region_size = __ATTR(size, 0444,
>                 region_size_show, NULL);
>
> -static ssize_t align_show(struct device *dev,
> +static ssize_t region_align_show(struct device *dev,
>                 struct device_attribute *attr, char *buf)
>  {
>         struct dax_region *dax_region = dev_get_drvdata(dev);
>
>         return sprintf(buf, "%u\n", dax_region->align);
>  }
> -static DEVICE_ATTR_RO(align);
> +static struct device_attribute dev_attr_region_align =
> +               __ATTR(align, 0400, region_align_show, NULL);
>
>  #define for_each_dax_region_resource(dax_region, res) \
>         for (res = (dax_region)->res.child; res; res = res->sibling)
> @@ -488,7 +489,7 @@ static umode_t dax_region_visible(struct kobject *kobj, struct attribute *a,
>  static struct attribute *dax_region_attributes[] = {
>         &dev_attr_available_size.attr,
>         &dev_attr_region_size.attr,
> -       &dev_attr_align.attr,
> +       &dev_attr_region_align.attr,
>         &dev_attr_create.attr,
>         &dev_attr_seed.attr,
>         &dev_attr_delete.attr,
> @@ -855,14 +856,13 @@ static ssize_t size_show(struct device *dev,
>         return sprintf(buf, "%llu\n", size);
>  }
>
> -static bool alloc_is_aligned(struct dax_region *dax_region,
> -               resource_size_t size)
> +static bool alloc_is_aligned(resource_size_t size, unsigned long align)

For type safety, let's make this take @dev_dax as a parameter. For the
dev_dax_set_align() case I think it is ok to provisionally adjust
dev_dax->align under the lock before entry and revert to the old
alignment on failure.

I can fix that up locally on applying.