linux-kernel - Re: [Xen-devel] [PATCH v2] xen-blkfront: remove type check from blkfront_setup

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Message-Id: <52D3FF0E02000078001131A5@nat28.tlf.novell.com>
Date:	Mon, 13 Jan 2014 13:58:22 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"David Vrabel" <david.vrabel@...rix.com>
Cc:	"Olaf Hering" <olaf@...fle.de>,
	"Ian Campbell" <Ian.Campbell@...rix.com>,
	<xen-devel@...ts.xen.org>, <boris.ostrovsky@...cle.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH v2] xen-blkfront: remove type check
 from blkfront_setup_discard

>>> On 13.01.14 at 14:45, David Vrabel <david.vrabel@...rix.com> wrote:
> On 13/01/14 13:16, Jan Beulich wrote:
>>>>> On 13.01.14 at 14:00, Ian Campbell <Ian.Campbell@...rix.com> wrote:
>>> On Mon, 2014-01-13 at 12:34 +0000, Jan Beulich wrote:
>>>>>>> On 13.01.14 at 13:01, Olaf Hering <olaf@...fle.de> wrote:
>>>>> On Mon, Jan 13, Jan Beulich wrote:
>>>>>
>>>>>> You can't do this in one go - the first two and the last one may be
>>>>>> set independently (and are independent in their meaning), and
>>>>>> hence need to be queried independently (xenbus_gather() fails
>>>>>> on the first absent value).
>>>>>
>>>>> Yes, thats the purpose. Since the properties are required its an all or
>>>>> nothing thing. If they are truly optional then blkif.h should be updated
>>>>> to say that.
>>>>
>>>> They _are_ optional.
>>>
>>> But is it true that either they are all present or they are all absent?
>> 
>> No, it's not. discard-secure is independent of the other two (but
>> those other two are tied together).
> 
> Can we have a patch to blkif.h that clarifies this?
> 
> e.g.,
> 
> feature-discard
> 
>    ...
> 
>    discard-granularity and discard-offset must also be present if
>    feature-discard is enabled

It would be "may" here too afaict. But I'll defer to Konrad, who
has done more work in this area...

Jan

>    discard-secure may also be present if feature-discard is enabled.
> 
> David



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