linux-kernel - Re: [PATCH] request_firmware: skip timeout if userspace was not notified

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Message-ID: <20070807125844.4d756b04@gondolin.boeblingen.de.ibm.com>
Date:	Tue, 7 Aug 2007 12:58:44 +0200
From:	Cornelia Huck <cornelia.huck@...ibm.com>
To:	Javier Pello <javier.pello@...c.es>
Cc:	linux-kernel@...r.kernel.org, Greg KH <greg@...ah.com>
Subject: Re: [PATCH] request_firmware: skip timeout if userspace was not
 notified

On Mon, 06 Aug 2007 22:23:07 +0200,
Javier Pello <javier.pello@...c.es> wrote:

> > > 2. The second part changes _request_firmware in
> > > drivers/base/firmware_class.c to actually check the return value
> > > of kobject_uevent and skip the loading_timeout delay if the
> > > loading event was not delivered to userspace at all.
> > 
> > Note that kobject_uevent() returns 0 if the event has been filtered.
> 
> Oops, yes, I had not noticed. This brings another point: When should
> kobject_uevent return a "failure"? The code, as it is, only returns a
> failure when things are really wrong (out of memory, etc.), and
> returns success when the event was simply dropped. This is reasonable
> behaviour, but it prevents callers from knowing whether the event was
> actually delivered (which is what request_firmware needs). On the
> other hand, my patch tries to make nondelivery an error, but on
> second thoughts that could prevent the caller from telling hard
> errors from simple nondelivery.

You could say that not delivering is caused by a hard error when trying
to deliver, though. OTOH, filtering an event is certainly not an error.

> I can think of two possibilities
> to sort this out:
> 
> - kobject_uevent returns an error code both on a hard error and
> on nondelivery; the error codes for both situations are different,
> so the caller can tell them apart.

Tough. For example, both today's kobject_uevent() and
call_usermodehelper() may return -ENOMEM.

> 
> - kobject_uevent returns an error code (<0) only on a hard error,
> returns 0 on nondelivery and 1 on delivery; this makes things
> even clearer.

Hm, I have an aversion against tri-state return values :( OTOH, a)
callers generally don't care and b) it is in line with how
kobject_uevent() is defined if !CONFIG_HOTPLUG.

- Use an extra parameter in which successful delivery can be indicated.
Make this
int kobject_uevent_env_check(struct kobject *kobject,
			     enum kobject_action action,
			     char *envp[], int delivered);
so existing callers that don't care don't have to be changed.

> 
> I am biased towards the latter. Of course, we can do anything as
> the return value is actually never used, but I would still like
> to know other opinions about what the right thing is.
-
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