Message-ID: <1440492739.2192.7.camel@sipsolutions.net>
Subject: Re: [PATCH v2 0/6] perf: Introduce extended syscall error reporting
From: Johannes Berg <johannes@sipsolutions.net>
To: Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Ingo Molnar <mingo@redhat.com>
Cc: linux-kernel@vger.kernel.org, adrian.hunter@intel.com,
        Arnaldo Carvalho de Melo <acme@infradead.org>,
        Vince Weaver <vince@deater.net>, Stephane Eranian <eranian@google.com>
Date: Tue, 25 Aug 2015 10:52:19 +0200
In-Reply-To: <1440426780-27227-1-git-send-email-alexander.shishkin@linux.intel.com>
References: <1440426780-27227-1-git-send-email-alexander.shishkin@linux.intel.com>
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On Mon, 2015-08-24 at 17:32 +0300, Alexander Shishkin wrote:

> This time around, I employed a linker trick to convert the structures
> containing extended error information into integers, which are then
> made to look just like normal error codes so that IS_ERR_VALUE() and
> friends would still work correctly on them. So no extra pointers in
> the struct perf_event or anywhere else; the extended error codes are
> passed around like normal error codes. They only need to be converted
> in syscalls' topmost return statements. This is done in 1/6.
> 

For the record, as we discussed separately, I'd love to see this move
to more general infrastructure. In wireless (nl80211), for example, we
have a few hundred (!) callsites returning -EINVAL, mostly based on
malformed netlink attributes, and it can be very difficult to figure
out what went wrong; debugging mostly employs a variation of Hugh's
trick.

It would be absolutely necessary to support modules, however that could
get tricky: unless we pass a THIS_MODULE through in some way to
netlink_ack() (in the nl80211 case) we'd have to store the actual index
inside the err_site and assign it on module load somehow. Passing the
module pointer seems better, but has even more wrinkles like what to do
when the error came from a nested call (e.g. nla_parse()) that's in a
different modules ...


Unrelated to all that - maybe perf_errno_to_site() should have some
range checking?

johannes
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