From: Darren Hart <dvhart@infradead.org>
To: Frans Klaver <fransklaver@gmail.com>
Cc: Henrique de Moraes Holschuh <hmh@hmh.eng.br>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Corentin Chary <corentin.chary@gmail.com>,
Rafael Wysocki <rafael.j.wysocki@intel.com>,
acpi4asus-user <acpi4asus-user@lists.sourceforge.net>,
platform-driver-x86 <platform-driver-x86@vger.kernel.org>,
linux-kernel@vger.kernel.org,
linux-acpi <linux-acpi@vger.kernel.org>,
"H. Peter Anvin" <hpa@linux.intel.com>
Subject: Re: [PATCH 10/13] eeepc-laptop: compare proper return values in get_cpufv
Date: Wed, 17 Sep 2014 09:12:23 -0700 [thread overview]
Message-ID: <20140917161223.GA5697@vmdeb7> (raw)
In-Reply-To: <CAH6sp9N8uWaiuPtqqcEgnyqzR=AUg6i-RwWpij-GQ-fE9AS+9g@mail.gmail.com>
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
> <hmh@hmh.eng.br> 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
next prev parent reply other threads:[~2014-09-17 16:12 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-12 23:06 [PATCH 00/13] eeepc-laptop cleanups Frans Klaver
2014-09-12 23:06 ` [PATCH 01/13] eeepc-laptop: coding style: fix indentation Frans Klaver
2014-09-12 23:06 ` [PATCH 02/13] eeepc-laptop: coding style: add curly braces around else compound Frans Klaver
2014-09-12 23:06 ` [PATCH 03/13] " Frans Klaver
2014-09-15 19:41 ` Darren Hart
2014-09-15 19:58 ` Frans Klaver
2014-09-12 23:06 ` [PATCH 04/13] eeepc-laptop: use symbolic permissions in device attributes Frans Klaver
2014-09-12 23:06 ` [PATCH 05/13] eeepc-laptop: use DEVICE_ATTR to instantiate device_attributes Frans Klaver
2014-09-12 23:28 ` Greg Kroah-Hartman
2014-09-14 22:05 ` Frans Klaver
2014-09-12 23:06 ` [PATCH 06/13] eeepc-laptop: pull out ACPI_STORE_FUNC and ACPI_SHOW_FUNC macros Frans Klaver
2014-09-12 23:06 ` [PATCH 07/13] eeepc-laptop: make disp attribute really write-only Frans Klaver
2014-09-15 20:00 ` Darren Hart
2014-09-15 20:01 ` Frans Klaver
2014-09-12 23:06 ` [PATCH 08/13] eeepc-laptop: pull out SENSOR_STORE_FUNC and SENSOR_SHOW_FUNC macros Frans Klaver
2014-09-12 23:06 ` [PATCH 09/13] eeepc-laptop: make fan1_input really read-only Frans Klaver
2014-09-12 23:06 ` [PATCH 10/13] eeepc-laptop: compare proper return values in get_cpufv Frans Klaver
2014-09-15 21:49 ` Darren Hart
2014-09-15 21:51 ` Greg Kroah-Hartman
2014-09-15 21:55 ` Frans Klaver
2014-09-16 11:54 ` Frans Klaver
2014-09-16 20:52 ` Darren Hart
2014-09-16 21:10 ` Frans Klaver
2014-09-16 23:39 ` Darren Hart
2014-09-16 21:27 ` Darren Hart
2014-09-16 21:33 ` Greg Kroah-Hartman
2014-09-16 21:40 ` Frans Klaver
2014-09-16 21:43 ` Darren Hart
2014-09-17 10:34 ` Henrique de Moraes Holschuh
2014-09-17 11:57 ` Frans Klaver
2014-09-17 16:12 ` Darren Hart [this message]
2014-09-12 23:06 ` [PATCH 11/13] eeepc-laptop: propagate errors from get_cpufv Frans Klaver
2014-09-15 21:50 ` Darren Hart
2014-09-12 23:06 ` [PATCH 12/13] eeepc-laptop: store_cpufv: return error if set_acpi fails Frans Klaver
2014-09-12 23:06 ` [PATCH 13/13] eeepc-laptop: return -ENXIO if acpi getter or setter fails Frans Klaver
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