Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754951AbbHYJeT (ORCPT ); Tue, 25 Aug 2015 05:34:19 -0400 Received: from s3.sipsolutions.net ([5.9.151.49]:38066 "EHLO sipsolutions.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751726AbbHYJeS (ORCPT ); Tue, 25 Aug 2015 05:34:18 -0400 Message-ID: <1440495246.2192.13.camel@sipsolutions.net> Subject: Re: [PATCH v2 0/6] perf: Introduce extended syscall error reporting From: Johannes Berg To: Ingo Molnar Cc: Alexander Shishkin , Peter Zijlstra , Ingo Molnar , linux-kernel@vger.kernel.org, adrian.hunter@intel.com, Arnaldo Carvalho de Melo , Vince Weaver , Stephane Eranian , Linus Torvalds , Andrew Morton , Thomas Gleixner , Borislav Petkov , "H. Peter Anvin" Date: Tue, 25 Aug 2015 11:34:06 +0200 In-Reply-To: <20150825091740.GA23488@gmail.com> (sfid-20150825_111744_580370_78C27B08) References: <1440426780-27227-1-git-send-email-alexander.shishkin@linux.intel.com> <1440492739.2192.7.camel@sipsolutions.net> <20150825090252.GB22414@gmail.com> <20150825091740.GA23488@gmail.com> (sfid-20150825_111744_580370_78C27B08) Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.16.3-1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2370 Lines: 58 On Tue, 2015-08-25 at 11:17 +0200, Ingo Molnar wrote: > > If we do that then we don't even have to introduce per system call error code > conversion, but could unconditionally save the last extended error info in the > task struct and continue - this could be done very cheaply with the linker trick > driven integer ID. > > I.e. system calls could opt in to do: > > > return err_str(-EBUSY, "perf/x86: BTS conflicts with active events"); > > and the overhead of this would be minimal, we'd essentially do something like this > to save the error: > > > current->err_code = code; > > where 'code' is a build time constant in essence. > > We could use this even in system calls where the error path is performance > critical, as all the string recovery and copying overhead would be triggered by > applications that opt in via the new system call: > > > struct err_desc { > > const char *message; > > const char *owner; > > const int code; > > }; > > > SyS_err_get_desc(struct err_desc *err_desc __user); > > [ Which could perhaps be a prctl() extension as well (PR_GET_ERR_DESC): finally > some truly matching functionality for prctl(). ] > > Hm? That's neat in a way, but doesn't work in general I think. Considering the wifi case, or more generally any netlink based protocol, the syscall (sendmsg) won't return an error, but a subsequent recvmsg() (which also won't return an error) returns an error message [in the sense of a protocol message, not a human readable message] to a buffer provided by the application. However, this message can be extended relatively easily to include the string information, but the syscall/prctl wouldn't work since the syscalls didn't actually fail. However, it could possibly help with the namespace/module issue if you also store THIS_MODULE (or perhaps instead a pointer to the module's error table) in the task. Again not in the netlink case though, I think, that will always require special handling [although there it could be stored away in the socket or so, similar to the task] johannes -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/