From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756169AbaIQQMb (ORCPT ); Wed, 17 Sep 2014 12:12:31 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:48788 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755608AbaIQQM1 (ORCPT ); Wed, 17 Sep 2014 12:12:27 -0400 Date: Wed, 17 Sep 2014 09:12:23 -0700 From: Darren Hart To: Frans Klaver Cc: Henrique de Moraes Holschuh , Greg Kroah-Hartman , Corentin Chary , Rafael Wysocki , acpi4asus-user , platform-driver-x86 , linux-kernel@vger.kernel.org, linux-acpi , "H. Peter Anvin" Subject: Re: [PATCH 10/13] eeepc-laptop: compare proper return values in get_cpufv Message-ID: <20140917161223.GA5697@vmdeb7> References: <1410563212-31565-1-git-send-email-fransklaver@gmail.com> <1410563212-31565-11-git-send-email-fransklaver@gmail.com> <20140915214902.GB64909@vmdeb7> <20140915215125.GA21435@kroah.com> <20140915215527.GC7867@gmail.com> <20140916205247.GA6856@vmdeb7> <20140916212715.GB6856@vmdeb7> <20140917103446.GA8594@khazad-dum.debian.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 17, 2014 at 01:57:33PM +0200, Frans Klaver wrote: > On Wed, Sep 17, 2014 at 12:34 PM, Henrique de Moraes Holschuh > wrote: > > On Tue, 16 Sep 2014, Darren Hart wrote: > >> - When reading and writing sysfs device attribute files, avoid dependency > >> on specific error codes wherever possible. This minimizes coupling to > >> the error handling implemementation within the kernel. > >> > >> In general, failures to read or write sysfs device attributes shall > >> propogate errors wherever possible. Common errors include, but are not > >> limited to: > >> > >> -EIO: The read or store operation is not supported, typically returned by > >> the sysfs system itself if the read or store pointer is NULL. > >> > >> -ENXIO: The read or store operation failed > > > > from errno(3): > > EIO Input/output error (POSIX.1) > > ENXIO No such device or address (POSIX.1) > > > > It makes sense to retry EIO. ENXIO means there's nobody listening at the > > time, and isn't usually retried. > > > > The device-based interfaces get it right. A typical example is the > > cpu-based devices, where ENXIO means "no such processor", while EIO means > > "whatever you're trying to do failed", so a MSR read would return ENXIO if > > the processor core is offline/doesn't exist, and EIO if the processor core > > is there, but raised a #GP when the MSR read was attempted. > > Here's something I don't quite understand. How should one then > distinguish between sysfs's use of EIO "can't (read from|write to) > this file", and this example's EIO "something went wrong, you might > want to try again"? Why not use EAGAIN "Resource temporarily > unavailable" in the case where trying again makes sense? I wouldn't > normally retry the last operation if I was just told something > actually went wrong. > > I've only been at it for a couple of weeks, but I get the impression > that sysfs has never really been guided regarding error codes, or has > gone to live its own life now kept in check with "don't change the > errors, it may break userspace". Does that make sense? Right, this was the distinction I was trying to make with the above description. Henrique's points are valid, but based on the sysfs subsystem already using EIO in the way that it does, I felt the above made sense. That said, I'm not personally tied to them, it's just what I have derived from recent discussions on the subject and what I observed in existing usage. -- Darren Hart Intel Open Source Technology Center