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

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Message-ID: <54292707.90008@gmail.com>
Date:	Mon, 29 Sep 2014 17:31:51 +0800
From:	Chen Gang <gang.chen.5i5j@...il.com>
To:	Jan Beulich <JBeulich@...e.com>, Juergen Gross <JGross@...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 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).


Thanks
-- 
Chen Gang

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