Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756798AbcJTVWX (ORCPT ); Thu, 20 Oct 2016 17:22:23 -0400 Received: from mx1.redhat.com ([209.132.183.28]:47272 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756403AbcJTVWW (ORCPT ); Thu, 20 Oct 2016 17:22:22 -0400 Date: Thu, 20 Oct 2016 15:22:20 -0600 From: Alex Williamson To: Kirti Wankhede Cc: , , , , , , , , Subject: Re: [PATCH v9 10/12] vfio: Add function to get device_api string from vfio_device_info.flags Message-ID: <20161020152220.57f6ee06@t450s.home> In-Reply-To: <6687c068-33f0-c437-3106-bbd1d22f4d81@nvidia.com> References: <1476739332-4911-1-git-send-email-kwankhede@nvidia.com> <1476739332-4911-11-git-send-email-kwankhede@nvidia.com> <20161020133403.08828f47@t450s.home> <20161020150501.39f28c7e@t450s.home> <6687c068-33f0-c437-3106-bbd1d22f4d81@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Thu, 20 Oct 2016 21:22:21 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4339 Lines: 114 On Fri, 21 Oct 2016 02:44:37 +0530 Kirti Wankhede wrote: > On 10/21/2016 2:35 AM, Alex Williamson wrote: > > On Fri, 21 Oct 2016 01:59:55 +0530 > > Kirti Wankhede wrote: > > > >> On 10/21/2016 1:04 AM, Alex Williamson wrote: > >>> On Tue, 18 Oct 2016 02:52:10 +0530 > >>> Kirti Wankhede wrote: > >>> > >>>> Function vfio_device_api_string() returns string based on flag set in > >>>> vfio_device_info's flag. This should be used by vendor driver to get string > >>>> based on flag for device_api attribute. > >>>> > >>>> Signed-off-by: Kirti Wankhede > >>>> Signed-off-by: Neo Jia > >>>> Change-Id: I42d29f475f02a7132ce13297fbf2b48f1da10995 > >>>> --- > >>>> drivers/vfio/vfio.c | 15 +++++++++++++++ > >>>> include/linux/vfio.h | 2 ++ > >>>> 2 files changed, 17 insertions(+) > >>>> > >>>> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c > >>>> index 10ef1c5fa762..aec470454a13 100644 > >>>> --- a/drivers/vfio/vfio.c > >>>> +++ b/drivers/vfio/vfio.c > >>>> @@ -1917,6 +1917,21 @@ int vfio_set_irqs_validate_and_prepare(struct vfio_irq_set *hdr, int num_irqs, > >>>> } > >>>> EXPORT_SYMBOL(vfio_set_irqs_validate_and_prepare); > >>>> > >>>> +const char *vfio_device_api_string(u32 flags) > >>>> +{ > >>>> + if (flags & VFIO_DEVICE_FLAGS_PCI) > >>>> + return "vfio-pci"; > >>>> + > >>>> + if (flags & VFIO_DEVICE_FLAGS_PLATFORM) > >>>> + return "vfio-platform"; > >>>> + > >>>> + if (flags & VFIO_DEVICE_FLAGS_AMBA) > >>>> + return "vfio-amba"; > >>>> + > >>>> + return ""; > >>>> +} > >>>> +EXPORT_SYMBOL(vfio_device_api_string); > >>>> + > >>>> /* > >>>> * Pin a set of guest PFNs and return their associated host PFNs for local > >>>> * domain only. > >>>> diff --git a/include/linux/vfio.h b/include/linux/vfio.h > >>>> index 31d059f1649b..fca2bf23c4f1 100644 > >>>> --- a/include/linux/vfio.h > >>>> +++ b/include/linux/vfio.h > >>>> @@ -116,6 +116,8 @@ extern int vfio_set_irqs_validate_and_prepare(struct vfio_irq_set *hdr, > >>>> int num_irqs, int max_irq_type, > >>>> size_t *data_size); > >>>> > >>>> +extern const char *vfio_device_api_string(u32 flags); > >>>> + > >>>> struct pci_dev; > >>>> #ifdef CONFIG_EEH > >>>> extern void vfio_spapr_pci_eeh_open(struct pci_dev *pdev); > >>> > >>> Couldn't this simply be a #define in the uapi header? > >>> > >>> #define VFIO_DEVICE_PCI_API_STRING "vfio-pci" > >>> > >>> I don't really see why we need a lookup function. > >>> > >> > >> String is tightly coupled with the FLAG, right? > >> Instead user need to take care of making sure to return proper string, > >> and don't mis-match the string, I think having function is easier. > > > > That's exactly why I proposed putting the #define string in the uapi, > > by that I mean the vfio uapi header. That keeps the tight coupling to > > the flag, they're both defined in the same place, plus it gives > > userspace a reference so they're not just inventing a string to compare > > against. IOW, the vendor driver simply does an sprintf of > > VFIO_DEVICE_PCI_API_STRING and userspace (ie. libvirt) can do a strcmp > > with VFIO_DEVICE_PCI_API_STRING from the same header and everybody > > arrives at the same result. > > > >> Vendor driver should decide the type of device they want to expose and > >> set the flag, using this function vendor driver would return string > >> which is based on flag they set. > > > > Being a function adds no intrinsic value and being in a uapi header does > > add value to userspace. Thanks, > > > > Ok. The strings should be in uapi, but having function (like below) to > return proper string based on flag would be good to have for vendor driver. > > +const char *vfio_device_api_string(u32 flags) > +{ > + if (flags & VFIO_DEVICE_FLAGS_PCI) > + return VFIO_DEVICE_API_PCI_STRING; > + > + if (flags & VFIO_DEVICE_FLAGS_PLATFORM) > + return VFIO_DEVICE_API_PLATFORM_STRING; > + > + if (flags & VFIO_DEVICE_FLAGS_AMBA) > + return VFIO_DEVICE_API_AMBA_STRING; > + > + return ""; > +} > +EXPORT_SYMBOL(vfio_device_api_string); I disagree, it's pointless maintenance overhead. It's yet another function that we need to care about for kABI and it offers almost no value. Thanks, Alex