linux-kernel - Re: [PATCH v1] : Switch to use new generic UUID API

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Message-Id: <5FF168CC-9372-4DE5-BF62-DD3A2EE08384@javigon.com>
Date:   Thu, 24 Jan 2019 15:36:47 +0100
From:   Javier González <javier@...igon.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Christoph Hellwig <hch@....de>,
        Matias Bjørling <mb@...htnvm.io>,
        linux-block@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] : Switch to use new generic UUID API


> On 24 Jan 2019, at 15.13, Andy Shevchenko <andy.shevchenko@...il.com> wrote:
> 
> On Thu, Jan 24, 2019 at 3:45 PM Javier González <javier@...igon.com> wrote:
>>> On 24 Jan 2019, at 14.36, Andy Shevchenko <andy.shevchenko@...il.com> wrote:
>>> On Thu, Jan 24, 2019 at 3:19 PM Javier González <javier@...igon.com> wrote:
>>>>> On 24 Jan 2019, at 13.16, Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:
> 
>>>>> header.uuid is defined using __u8 type, I'm not sure we can use guid_t there.
>>>> 
>>>> We can turn it into a guid_t and bump the minor version.
>>> 
>>> It's not so easy. __uXX types are dedicated for external APIs. guid_t
>>> is kernel internal type disregard of (still) presence some uapi bits.
>>> So, the question is those __uXX types in the driver definition is a
>>> simple mistake, (weird) style decision, or what?
>> 
>> I would define it as a mistake and I think it is worth fixing it. At the
>> moment we are only using this uuid for recovery purposes, to discard
>> data from a different pblk instance,
> 
> Does this come from outside of the kernel in any mean (user space,
> data from device, etc)?
> It sounds to me like it does. In this case there is no mistake and we
> may not use guid_t there.

pblk manages the metadata layout without involvement of the device or
user space, so no, no dependency at this moment.

It is not pushed anywhere yet, but I have been working on a tool to make
a pblk recovery tool to enable FTL repairs if something fails in the
kernel recovery path. Here, I use this uuid to identify the
instance - is there a way to reconcile guid_t with user space, which
currently uses the __u8?

Javier

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