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Date:   Mon, 8 Jul 2019 08:05:27 -0700
From:   Stephen Hemminger <stephen@networkplumber.org>
To:     Randy Dunlap <rdunlap@infradead.org>
Cc:     Haiyang Zhang <haiyangz@microsoft.com>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-pci <linux-pci@vger.kernel.org>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Matthew Wilcox <willy@infradead.org>,
        Jake Oshins <jakeo@microsoft.com>,
        KY Srinivasan <kys@microsoft.com>,
        Sasha Levin <sashal@kernel.org>,
        Bjorn Helgaas <bhelgaas@google.com>,
        "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
        Dexuan Cui <decui@microsoft.com>,
        Yuehaibing <yuehaibing@huawei.com>
Subject: Re: [PATCH v2] PCI: hv: fix pci-hyperv build when SYSFS not enabled
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On Sun, 7 Jul 2019 10:46:22 -0700
Randy Dunlap <rdunlap@infradead.org> wrote:

> On 7/3/19 11:06 AM, Haiyang Zhang wrote:
> > 
> >   
> >> -----Original Message-----
> >> From: Randy Dunlap <rdunlap@infradead.org>
> >> Sent: Wednesday, July 3, 2019 12:59 PM
> >> To: LKML <linux-kernel@vger.kernel.org>; linux-pci <linux-  
> >> pci@vger.kernel.org>  
> >> Cc: Matthew Wilcox <willy@infradead.org>; Jake Oshins
> >> <jakeo@microsoft.com>; KY Srinivasan <kys@microsoft.com>; Haiyang
> >> Zhang <haiyangz@microsoft.com>; Stephen Hemminger
> >> <sthemmin@microsoft.com>; Sasha Levin <sashal@kernel.org>; Bjorn
> >> Helgaas <bhelgaas@google.com>; linux-hyperv@vger.kernel.org; Dexuan
> >> Cui <decui@microsoft.com>; Yuehaibing <yuehaibing@huawei.com>
> >> Subject: [PATCH v2] PCI: hv: fix pci-hyperv build when SYSFS not enabled
> >>
> >> From: Randy Dunlap <rdunlap@infradead.org>
> >>
> >> Fix build of drivers/pci/controller/pci-hyperv.o when
> >> CONFIG_SYSFS is not set/enabled by adding stubs for
> >> pci_create_slot() and pci_destroy_slot().
> >>
> >> Fixes these build errors:
> >>
> >> ERROR: "pci_destroy_slot" [drivers/pci/controller/pci-hyperv.ko] undefined!
> >> ERROR: "pci_create_slot" [drivers/pci/controller/pci-hyperv.ko] undefined!
> >>
> >> Fixes: a15f2c08c708 ("PCI: hv: support reporting serial number as slot
> >> information")
> >>
> >> Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
> >> Cc: Matthew Wilcox <willy@infradead.org>
> >> Cc: Jake Oshins <jakeo@microsoft.com>
> >> Cc: "K. Y. Srinivasan" <kys@microsoft.com>
> >> Cc: Haiyang Zhang <haiyangz@microsoft.com>
> >> Cc: Stephen Hemminger <sthemmin@microsoft.com>
> >> Cc: Sasha Levin <sashal@kernel.org>
> >> Cc: Bjorn Helgaas <bhelgaas@google.com>
> >> Cc: linux-pci@vger.kernel.org
> >> Cc: linux-hyperv@vger.kernel.org
> >> Cc: Dexuan Cui <decui@microsoft.com>
> >> Cc: Yuehaibing <yuehaibing@huawei.com>
> >> ---
> >> v2:
> >> - provide non-CONFIG_SYSFS stubs for pci_create_slot() and
> >>   pci_destroy_slot() [suggested by Matthew Wilcox <willy@infradead.org>]
> >> - use the correct Fixes: tag [Dexuan Cui <decui@microsoft.com>]
> >>
> >>  include/linux/pci.h |   12 ++++++++++--
> >>  1 file changed, 10 insertions(+), 2 deletions(-)
> >>
> >> --- lnx-52-rc7.orig/include/linux/pci.h
> >> +++ lnx-52-rc7/include/linux/pci.h
> >> @@ -25,6 +25,7 @@
> >>  #include <linux/ioport.h>
> >>  #include <linux/list.h>
> >>  #include <linux/compiler.h>
> >> +#include <linux/err.h>
> >>  #include <linux/errno.h>
> >>  #include <linux/kobject.h>
> >>  #include <linux/atomic.h>
> >> @@ -947,14 +948,21 @@ int pci_scan_root_bus_bridge(struct pci_
> >>  struct pci_bus *pci_add_new_bus(struct pci_bus *parent, struct pci_dev
> >> *dev,
> >>  				int busnr);
> >>  void pcie_update_link_speed(struct pci_bus *bus, u16 link_status);
> >> +#ifdef CONFIG_SYSFS
> >> +void pci_dev_assign_slot(struct pci_dev *dev);
> >>  struct pci_slot *pci_create_slot(struct pci_bus *parent, int slot_nr,
> >>  				 const char *name,
> >>  				 struct hotplug_slot *hotplug);
> >>  void pci_destroy_slot(struct pci_slot *slot);
> >> -#ifdef CONFIG_SYSFS
> >> -void pci_dev_assign_slot(struct pci_dev *dev);
> >>  #else
> >>  static inline void pci_dev_assign_slot(struct pci_dev *dev) { }
> >> +static inline struct pci_slot *pci_create_slot(struct pci_bus *parent,
> >> +					       int slot_nr,
> >> +					       const char *name,
> >> +					       struct hotplug_slot *hotplug) {
> >> +	return ERR_PTR(-EINVAL);
> >> +}
> >> +static inline void pci_destroy_slot(struct pci_slot *slot) { }
> >>  #endif
> >>  int pci_scan_slot(struct pci_bus *bus, int devfn);
> >>  struct pci_dev *pci_scan_single_device(struct pci_bus *bus, int devfn);
> >>  
> > 
> > The serial number in slot info is used to match VF NIC with Synthetic NIC.
> > Without selecting SYSFS, the SRIOV feature will fail on VM on Hyper-V and
> > Azure. The first version of this patch should be used.
> > 
> > @Stephen Hemminger how do you think?

Haiyang is right, accelerated networking won't work if slot is not recorded.

So the original patch (to depend on SYSFS) or using "select SYSFS" is
are necessary.

The whole thing is a bit of "angels dancing on the head of a pin" because
there is no good reason to build kernel without SYSFS in real world.
It would just be looking for trouble. As far as I can tell it is all
about getting "make randconfig" to work in more cases.