linux-kernel - Re: [PATCH] Drivers: hv: vmbus: Return -EINVAL for the sys files for unopened channels

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Message-ID: <20181217101703.78e8bb3f@xeon-e3>
Date:   Mon, 17 Dec 2018 10:17:03 -0800
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Dexuan Cui <decui@...rosoft.com>
Cc:     "'gregkh@...uxfoundation.org'" <gregkh@...uxfoundation.org>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>,
        "'devel@...uxdriverproject.org'" <devel@...uxdriverproject.org>,
        "'olaf@...fle.de'" <olaf@...fle.de>,
        "'jasowang@...hat.com'" <jasowang@...hat.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        Sasha Levin <Alexander.Levin@...rosoft.com>,
        "'apw@...onical.com'" <apw@...onical.com>,
        vkuznets <vkuznets@...hat.com>
Subject: Re: [PATCH] Drivers: hv: vmbus: Return -EINVAL for the sys files
 for unopened channels

On Mon, 17 Dec 2018 18:00:29 +0000
Dexuan Cui <decui@...rosoft.com> wrote:

> > From: Stephen Hemminger <stephen@...workplumber.org>
> > On Thu, 13 Dec 2018 16:35:43 +0000
> > Dexuan Cui <decui@...rosoft.com> wrote:
> >   
> > > Before 98f4c651762c, we returned zeros for unopened channels.
> > > With 98f4c651762c, we started to return random on-stack values.
> > >
> > > We'd better return -EINVAL instead.  
> > 
> > The concept looks fine, but maybe it would be simpler to move it into
> > hv_ringbuffer_get_debuginfo and have it return an error code.
> > 
> > Since so much of the code is repeated, I would probably make a
> > macro which generates the code as well.
> > 
> > Something like this:  
> 
> Thanks, Stephen! Now the patch has been in char-misc's char-misc-linus
> branch, so IMO we may as well leave it as is (considering the code here is
> unlikely to be frqeuencly changed), and we have a smaller patch this way. :-)
> 
> But, yes, I agree with you that generally we should make a common
> function to avoid duplicate code.
> 
> Thanks,
> -- Dexuan

The old code was risky because it would silently return stack garbage.
Having an error check in get_debuginfo would eliminate that.