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 09:41:06 +0100
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Chen Gang" <gang.chen.5i5j@...il.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 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().

Jan

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