From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757702Ab3BYVXu (ORCPT ); Mon, 25 Feb 2013 16:23:50 -0500 Received: from mail-oa0-f45.google.com ([209.85.219.45]:50552 "EHLO mail-oa0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753342Ab3BYVXr (ORCPT ); Mon, 25 Feb 2013 16:23:47 -0500 MIME-Version: 1.0 In-Reply-To: <1361810245.2975.14.camel@lorien2> References: <1360623637.2950.63.camel@lorien2> <1361810245.2975.14.camel@lorien2> From: Bjorn Helgaas Date: Mon, 25 Feb 2013 14:23:27 -0700 Message-ID: Subject: Re: [PATCH 1/4] pci: Add PCI_BUS() and PCI_DEVID() interfaces to return bus number and device id To: shuah.khan@hp.com Cc: dhowells@redhat.com, Joerg Roedel , paulmck@linux.vnet.ibm.com, linasvepstas@gmail.com, davej@redhat.com, tglx@linutronix.de, mtk.manpages@gmail.com, iommu@lists.linux-foundation.org, LKML , linux-pci@vger.kernel.org, shemminger@vyatta.com, jiang.liu@huawei.com, wangyijing@huawei.com, shuahkhan@gmail.com Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 25, 2013 at 9:37 AM, Shuah Khan wrote: > On Wed, 2013-02-20 at 18:19 -0700, Bjorn Helgaas wrote: >> On Mon, Feb 11, 2013 at 4:00 PM, Shuah Khan wrote: >> > pci defines PCI_DEVFN(), PCI_SLOT(), and PCI_FUNC() interfaces, however, >> > it doesn't have interfaces to return PCI bus and PCI device id. Drivers >> > (AMD IOMMU, and AER) implement module specific definitions for PCI_BUS() >> > and AMD_IOMMU driver also has a module specific interface to calculate PCI >> > device id from bus number and devfn. >> > >> > Add PCI_BUS and PCI_DEVID interfaces to return PCI bus number and PCI device >> > id respectively to avoid the need for duplicate definitions in other modules. >> > AER driver code and AMD IOMMU driver define PCI_BUS. AMD IOMMU driver defines >> > an interface to calculate device id from bus number, and devfn pair. >> > >> > Signed-off-by: Shuah Khan >> > --- >> > include/uapi/linux/pci.h | 4 ++++ >> > 1 file changed, 4 insertions(+) >> > >> > diff --git a/include/uapi/linux/pci.h b/include/uapi/linux/pci.h >> > index 3c292bc0..6b2c8b3 100644 >> > --- a/include/uapi/linux/pci.h >> > +++ b/include/uapi/linux/pci.h >> > @@ -30,6 +30,10 @@ >> > #define PCI_DEVFN(slot, func) ((((slot) & 0x1f) << 3) | ((func) & 0x07)) >> > #define PCI_SLOT(devfn) (((devfn) >> 3) & 0x1f) >> > #define PCI_FUNC(devfn) ((devfn) & 0x07) >> > +#define PCI_DEVID(bus, devfn) ((((u16)bus) << 8) | devfn) >> > + >> > +/* return bus from PCI devid = ((u16)bus_number) << 8) | devfn */ >> > +#define PCI_BUS(x) (((x) >> 8) & 0xff) >> > >> > /* Ioctls for /proc/bus/pci/X/Y nodes. */ >> > #define PCIIOC_BASE ('P' << 24 | 'C' << 16 | 'I' << 8) >> >> David, can you point me at a description of include/uapi ... what is >> there and why, and how we should decide what new things go in >> include/uapi/linux/pci.h as opposed to include/linux/pci.h? Maybe >> there should be something in Documentation/? >> >> I'm guessing it's something to do with being exported to userland, but >> I'm not sure the things in this patch (PCI_DEV_ID, PCI_BUS) are really >> exportable in the sense of being used for syscalls, etc. >> > > Bjorn,David, > > Looks like the following thread answers some of the questions about when > this uapi export was done on the existing defines. > > https://lkml.org/lkml/2011/7/28/198 > > Sounds like the concern is that the older defines PCI_DEVFN, PCI_SLOT, > PCI_FUNC, and PCI_DEVID could be exported, but not the new ones I > added. I could find any discussion on whether these four older defines > are exportable or the reasons for the export in the above thread. I think David's disintegration script took include/linux/pci.h, left the #ifdef __KERNEL__ parts there, and moved everything else (which wasn't much) to include/uapi/linux/pci.h. It's obvious that the PCIIOC_ #defines need to be exported to user-space for ioctls. It's not obvious to me why PCI_DEVFN, PCI_SLOT, and PCI_FUNC need to be exported to user-space. But I can imagine user-space using functionality like that, even if it's not connected to a kernel interface. I assume the intent of the disintegration is that only include/uapi would be exposed to user-space, so keeping those definitions in include/linux/pci.h would break any user programs that used them. > So the question is if uapi/linux.pci.h isn't the right place, do you > have a recommendation on where they belong. The only alternative I can > think of is include/linux/pci.h. It makes functional and logical sense > to add the new defines to where the existing ones are defines. At least, > not knowing the details of the change that moved PCI_DEVFN etc. to > uapi/pci.h, that is my conclusion. Using the linux-fullhist tree, I found these: 059d367 Import 2.1.82 -- moved PCI_DEVFN outside #ifdef __KERNEL__ b039547 Import 2.1.76 -- PCI_DEVFN was inside #ifdef __KERNEL__ f6d9739 Import 2.1.68pre1 -- added #ifdef __KERNEL__ (enclosing PCI_DEVFN) 940649f Import 1.3.0 -- added PCI_DEVFN There's no indication of *why* PCI_DEVFN was exported, of course. Bottom line, I think it's reasonable to keep PCI_DEVFN, et al., in uapi/linux/pci.h to keep from breaking user-programs, even though if we were adding them today we would probably put them in the kernel-only linux/pci.h. For the new ones you're adding, I'd propose putting them in the kernel-only linux/pci.h because we know no user programs use them. It's not nice and consistent, but it does follow the simple rule of "don't expose things to user-space unnecessarily." We might want to add a comment to keep somebody from cleaning it up later. Bjorn