linux-kernel - Re: [PATCH v2] pci: export class IDs from pci

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Message-ID: <20150402215921.GA3942@kroah.com>
Date:	Thu, 2 Apr 2015 23:59:21 +0200
From:	Greg KH <gregkh@...uxfoundation.org>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>, linux-kernel@...r.kernel.org,
	Jonathan Corbet <corbet@....net>,
	"David S. Miller" <davem@...emloft.net>,
	Hans Verkuil <hans.verkuil@...co.com>,
	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	stephen hemminger <stephen@...workplumber.org>,
	Masahiro Yamada <yamada.m@...panasonic.com>,
	linux-pci@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-api@...r.kernel.org
Subject: Re: [PATCH v2] pci: export class IDs from pci_ids.h

On Thu, Apr 02, 2015 at 11:28:19PM +0200, Michael S. Tsirkin wrote:
> On Thu, Apr 02, 2015 at 03:53:47PM -0500, Bjorn Helgaas wrote:
> > On Mon, Mar 30, 2015 at 01:33:28PM +0200, Michael S. Tsirkin wrote:
> > > The basic class ID macros in pci_ids.h are pretty useful for userspace
> > > using the pci sysfs interface, and they aren't fundamentally different
> > > from the constants in pci_regs.h - both are defined in the
> > > pci spec.
> > > 
> > > At the moment userspace is forced to duplicate these macros
> > > (e.g. QEMU does this, so do seabios, gpxe, and others), it is better to
> > > expose them in /usr/include/linux/pci_ids.h so everyone can just include
> > > this header.
> > 
> > I agree that it would be nice for applications to get these definitions
> > from a single place, but I'm not sure that include/uapi/linux/pci_ids.h
> > needs to be that place.
> > 
> > These constants are just copies of what's in the spec, and I don't think
> > you're suggesting that the constants are necessary to use a kernel API.
> > 
> > I know the kernel does provide access to values via sysfs "class" files,
> > but the kernel is just passing the values through from the hardware.
> > That's analogous to reading the class with setpci, and I don't think it
> > leads to a requirement that the kernel export all the information about how
> > to interpret the class values.
> > 
> > I haven't looked at libpci or libudev, but it sounds like you think those
> > are not good solutions.  Is that because they don't currently have this
> > information?  People don't want to add dependencies on them?
> > 
> > Bjorn
> 
> People don't want to add dependencies on them.

So you want us to create yet-a-third-location for these values?  Both
libpci and libudev are on all systems.  And it's not a run-time
dependancy you are talking about here, but a build-time one, which is
quite different.  Having a build-time dependancy on packages that ship
with all Linux distributions seems acceptable to me.

thanks,

greg k-h
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