linux-kernel - Re: [PATCH] livepatch: core: Return ENOTSUPP instead of ENOSYS

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Message-ID: <20190129165054.vyi7n6in5v2omkpu@treble>
Date:   Tue, 29 Jan 2019 10:50:54 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Joe Lawrence <joe.lawrence@...hat.com>
Cc:     Alice Ferrazzi <alicef@...cef.me>, jeyu@...nel.org,
        jikos@...nel.org, mbenes@...e.cz, pmladek@...e.com,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        Alice Ferrazzi <alice.ferrazzi@...aclelinux.com>
Subject: Re: [PATCH] livepatch: core: Return ENOTSUPP instead of ENOSYS

On Mon, Jan 28, 2019 at 02:49:43PM -0500, Joe Lawrence wrote:
> On Sun, Jan 27, 2019 at 04:26:30AM +0900, Alice Ferrazzi wrote:
> > This patch fixes a checkpatch warning:
> >     WARNING: ENOSYS means 'invalid syscall nr' and nothing else
> > 
> > Signed-off-by: Alice Ferrazzi <alice.ferrazzi@...aclelinux.com>
> > ---
> >  kernel/livepatch/core.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> > index 5b77a7314e01..eea6b94fef89 100644
> > --- a/kernel/livepatch/core.c
> > +++ b/kernel/livepatch/core.c
> > @@ -897,7 +897,7 @@ int klp_register_patch(struct klp_patch *patch)
> >  
> >  	if (!klp_have_reliable_stack()) {
> >  		pr_err("This architecture doesn't have support for the livepatch consistency model.\n");
> > -		return -ENOSYS;
> > +		return -ENOTSUPP;
> >  	}
> >  
> >  	return klp_init_patch(patch);
> > -- 
> > 2.19.2
> > 
> 
> Hi Alice,
> 
> Patches should be based off the upstream livepatching tree, found here:
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/livepatching/livepatching.git
> 
> and in this case, the for-next branch, which holds patches that have
> already been queued up for the next release.  This one:
> 
>   958ef1e39d24 ("livepatch: Simplify API by removing registration step")
> 
> has moved the code in question from klp_register_patch() to
> klp_enable_patch().
> 
> 
> As far as the change itself, I don't have strong opinion about it
> either way.
> 
> On the one hand, there is the checkpatch warning and -ENOTSUPP reads
> more intuitively than -ENOSYS. 
> 
> However, the current pattern seems to be more prevelent in the kernel.
> I wonder if the checkpatch warning would be better specified for return
> values that are actually passed back to userspace.
> 
> Also, klp_register_patch(), now klp_enable_patch(), is exported for
> module use, though I don't believe anyone (samples / tests / kpatch /
> kgraft?) is inspecting which error value is returned.
> 
> I would defer to whichever convention the maintainers prefer here.

Based on the commit description from 91c9afaf97ee ("checkpatch.pl: new
instances of ENOSYS are errors"), it sounds like there was a decision at
Kernel Summit to limit ENOSYS to mean "bad syscall" and nothing else.

So I'm ok with this change, though the patch description should have a
little more background on why it's being done -- checkpatch.pl alone
isn't a good justification because some checkpatch warnings are best
taken with a grain of salt.

-- 
Josh