netdev - Re: [pci PATCH v5 1/4] pci: Add pci_sriov_configure_simple for PFs that don't manage VF resources

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Date:   Mon, 12 Mar 2018 13:17:00 -0700
From:   Alexander Duyck <alexander.duyck@...il.com>
To:     Keith Busch <keith.busch@...el.com>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        "Duyck, Alexander H" <alexander.h.duyck@...el.com>,
        linux-pci@...r.kernel.org, virtio-dev@...ts.oasis-open.org,
        kvm@...r.kernel.org, Netdev <netdev@...r.kernel.org>,
        "Daly, Dan" <dan.daly@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-nvme@...ts.infradead.org, netanel@...zon.com,
        Maximilian Heyne <mheyne@...zon.de>,
        "Wang, Liang-min" <liang-min.wang@...el.com>,
        "Rustad, Mark D" <mark.d.rustad@...el.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Christoph Hellwig <hch@....de>, dwmw@...zon.co.uk
Subject: Re: [pci PATCH v5 1/4] pci: Add pci_sriov_configure_simple for PFs
 that don't manage VF resources

On Mon, Mar 12, 2018 at 11:23 AM, Keith Busch <keith.busch@...el.com> wrote:
> On Mon, Mar 12, 2018 at 11:09:34AM -0700, Alexander Duyck wrote:
>> On Mon, Mar 12, 2018 at 10:40 AM, Keith Busch <keith.busch@...el.com> wrote:
>> > On Mon, Mar 12, 2018 at 10:21:29AM -0700, Alexander Duyck wrote:
>> >> diff --git a/include/linux/pci.h b/include/linux/pci.h
>> >> index 024a1beda008..9cab9d0d51dc 100644
>> >> --- a/include/linux/pci.h
>> >> +++ b/include/linux/pci.h
>> >> @@ -1953,6 +1953,7 @@ static inline void pci_mmcfg_late_init(void) { }
>> >>  int pci_vfs_assigned(struct pci_dev *dev);
>> >>  int pci_sriov_set_totalvfs(struct pci_dev *dev, u16 numvfs);
>> >>  int pci_sriov_get_totalvfs(struct pci_dev *dev);
>> >> +int pci_sriov_configure_simple(struct pci_dev *dev, int nr_virtfn);
>> >>  resource_size_t pci_iov_resource_size(struct pci_dev *dev, int resno);
>> >>  void pci_vf_drivers_autoprobe(struct pci_dev *dev, bool probe);
>> >>  #else
>> >
>> > I recommend stubbing 'pci_sriov_configure_simple' or defining it to
>> > NULL in the '#else' section here so you don't need to repeat the "#ifdef
>> > CONFIG_PCI_IOV" in each driver wishing to use this function. Otherwise
>> > looks fine to me.
>>
>> My concern with defining it as NULL is that somebody may end up
>> calling it in the future directly and that may end up causing issues.
>> One thought I have been debating is moving it to a different file. I
>> am just not sure where the best place to put something like this would
>> be. I could move this function to drivers/pci/pci.c if everyone is
>> okay with it and then I could just strip the contents out by wrapping
>> them in a #ifdef instead.
>
> Okay, instead of NULL, a stub implementation in the header file may
> suffice when CONFIG_PCI_IOV is not defined:
>
> static inline int pci_sriov_configure_simple(struct pci_dev *dev, int nr_virtfn)
> {
>         return -ENOSYS;
> }
>
> See pci_iov_virtfn_bus, pci_iov_virtfn_devfn, pci_iov_add_virtfn, or
> pci_enable_sriov for other examples.

No, I am aware of those. The problem is they aren't accessed as
function pointers. As such converting them to static inline functions
is easy. As I am sure you are aware an "inline" function doesn't
normally generate a function pointer.

Actually my original idea has been complicated further by the fact
that I realized my code is accessing functions that are static in the
iov.c file. I'll need to think about how to come up with a better
solution for this.