linux-kernel - Re: [Xen-devel] [PATCH] xen/xen-scsiback: Need go to fail after xenbus_dev

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Date:	Mon, 29 Sep 2014 17:59:10 +0800
From:	Chen Gang <gang.chen.5i5j@...il.com>
To:	Juergen Gross <jgross@...e.com>, Jan Beulich <JBeulich@...e.com>
CC:	David Vrabel <david.vrabel@...rix.com>,
	xen-devel@...ts.xenproject.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH] xen/xen-scsiback: Need go to fail after xenbus_dev_error()

On 9/29/14 17:34, Juergen Gross wrote:
> On 09/29/2014 11:31 AM, Chen Gang wrote:
>> On 9/29/14 16:41, Jan Beulich wrote:
>>>>>> On 29.09.14 at 06:32, <JGross@...e.com> wrote:
>>>> On 09/26/2014 06:38 PM, Chen Gang wrote:
>>>>> When failure occurs, after xenbus_dev_error(), need go to fail to let
>>>>> upper caller know about it.
>>>>>
>>>>> Signed-off-by: Chen Gang <gang.chen.5i5j@...il.com>
>>>>> ---
>>>>>    drivers/xen/xen-scsiback.c | 4 +++-
>>>>>    1 file changed, 3 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/xen/xen-scsiback.c b/drivers/xen/xen-scsiback.c
>>>>> index 847bc9c..3e430e1 100644
>>>>> --- a/drivers/xen/xen-scsiback.c
>>>>> +++ b/drivers/xen/xen-scsiback.c
>>>>> @@ -1222,8 +1222,10 @@ static int scsiback_probe(struct xenbus_device *dev,
>>>>>
>>>>>        err = xenbus_printf(XBT_NIL, dev->nodename, "feature-sg-grant", "%u",
>>>>>                    SG_ALL);
>>>>> -    if (err)
>>>>> +    if (err) {
>>>>>            xenbus_dev_error(dev, err, "writing feature-sg-grant");
>>>>> +        goto fail;
>>>>> +    }
>>>>>
>>>>>        xenbus_switch_state(dev, XenbusStateInitWait);
>>>>>        return 0;
>>>>>
>>>>
>>>> Hmm, not testing for failure was on purpose. Advertising this feature
>>>> is just for tuning purposes, not mandatory.
>>>>
>>>> OTOH it would really be a strange error if this xenbus_printf() fails
>>>> but all other operations are working, and signaling an error at the
>>>> time when it first shows up is a good thing. So:
>>>
>>> I disagree - failure to announce optional features should not lead to
>>> general failure. And this should be consistent across drivers; for
>>> existing examples see xen_blkbk_flush_diskcache() and
>>> xen_blkbk_discard().
>>>
>>
>> During scsiback_probe(), can we sure that "feature-sg-grant" is optional
>> feature? For me, only according to its name, I guess not: it is about
>> security which is always necessary in kernel (although SG_ALL).
> 
> It is optional. Otherwise the interface would be broken, as I've added
> this feature recently and "old" clients (pre 3.18) don't know about it.
> 
> The feature is NOT about security, but about capability to support
> larger SCSI requests than the old interface did.
> 

OK, thanks. All of you said sounds reasonable to me: "it is optional, need
print related warning and continue".

If no any additional reply within 2 days, I shall send patch v2 for it:

  "use dev_warn() instead of xenbus_dev_error() and remove 'fail' code block"


Thanks.
-- 
Chen Gang

Open, share, and attitude like air, water, and life which God blessed
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