linux-kernel - Re: [PATCH v2 0/6] perf: Introduce extended syscall error reporting

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Message-ID: <20150825090252.GB22414@gmail.com>
Date:	Tue, 25 Aug 2015 11:02:52 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Johannes Berg <johannes@...solutions.net>
Cc:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	adrian.hunter@...el.com,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Vince Weaver <vince@...ter.net>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH v2 0/6] perf: Introduce extended syscall error reporting


* Johannes Berg <johannes@...solutions.net> wrote:

> 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.

Absolutely, I suggested this as well earlier today, as the scheduler would like to 
make use of it in syscalls with extensible ABIs, such as sched_setattr().

If people really like this then we could go farther as well and add a standalone 
'extended errors system call' as well (SyS_errno_extended_get()), which would 
allow the recovery of error strings even for system calls that are not easily 
extensible. We could cache the last error description in the task struct.

Thanks,

	Ingo
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