From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753839AbbCJR0V (ORCPT ); Tue, 10 Mar 2015 13:26:21 -0400 Received: from mx1.redhat.com ([209.132.183.28]:39503 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752718AbbCJR0S (ORCPT ); Tue, 10 Mar 2015 13:26:18 -0400 Date: Tue, 10 Mar 2015 13:26:03 -0400 From: Peter Jones To: Andy Lutomirski Cc: Matt Fleming , "Kweh, Hock Leong" , Sam Protsenko , Ming Lei , Greg Kroah-Hartman , "Ong, Boon Leong" , LKML , "linux-efi@vger.kernel.org" Subject: Re: Re: [PATCH v2 3/3] efi: Capsule update with user helper interface Message-ID: <20150310172603.GF1208@fenchurch.internal.datastacks.com> References: <20150306213912.GA8020@fenchurch.internal.datastacks.com> <20150310122652.GA17573@codeblueprint.co.uk> <20150310152155.GB1208@fenchurch.internal.datastacks.com> <20150310154000.GD1208@fenchurch.internal.datastacks.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 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 Tue, Mar 10, 2015 at 08:51:59AM -0700, Andy Lutomirski wrote: > On Tue, Mar 10, 2015 at 8:40 AM, Peter Jones wrote: > > > >> >> So, for the sysfs interface, let's not allow loading from /lib. Let's > >> >> not require a userland tool. Let's just do, > >> >> > >> >> # echo /path/to/my/awesome/capsule.bin > /sys/../capsule > >> > > >> >> > >> >> and be done with it. > >> >> > >> >> Hmmm? > >> > > >> > I assume you're implying a) the capsule header with the guid is embedded > >> > in the .bin there already, and b) one contiguous write(2) with error > >> > reporting coming through something like vars.c's efi_status_to_err()? > >> > > >> > If so, yes, I prefer this API. > >> > > >> > >> Is using a char device really so bad? I have a "simple_char" that > >> makes this really easy that's pending review. > > > > As long as there's straightforward propagation of the EFI_STATUS return > > from UpdateCapsule() back, sysfs file vs char device makes very little > > difference to me. Either way it's open(), write(), close(). Using the > > runtime firmware upload interface designed for wifi and scsi devices is > > the part I don't really like. > > > > I'm not 100% happy with write(2) (which is all we have in sysfs) for > two reasons: > > 1. If we write a file name, eww. That's more complicated, requires > temporary files, has annoying mount namespace issues, etc. > > 2. If we write the full contents, we need to do it in a single call to > write. That means that we can't use cat, which mostly defeats the > purpose. In fact, using cat could be actively harmful. So if what we wind up with is: fd = open("/sys/.../capsule", O_RDWR); write(fd, buf, size/N); ... write(fd, buf + M*size/N, size/N); close(fd); You're suggesting the error code would post on close()? My worry about that is that I imagine a lot less code in the wild checks the error code on close() than on write() - though gnu cat does do so on both. But there are other questions still - will it post on fdatasync()? On fsync()? -- Peter