linux-kernel - RE: [PATCH] PCI: hv: Fix build error without CONFIG

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Date:   Sat, 1 Jun 2019 22:59:56 +0000
From:   Michael Kelley <mikelley@...rosoft.com>
To:     YueHaibing <yuehaibing@...wei.com>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "sashal@...nel.org" <sashal@...nel.org>,
        Dexuan Cui <decui@...rosoft.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: RE: [PATCH] PCI: hv: Fix build error without CONFIG_SYSFS

From: YueHaibing <yuehaibing@...wei.com>  Sent: Friday, May 31, 2019 8:09 AM
> 
> while building without CONFIG_SYSFS, fails as below:
> 
> drivers/pci/controller/pci-hyperv.o: In function 'hv_pci_assign_slots':
> pci-hyperv.c:(.text+0x40a): undefined reference to 'pci_create_slot'
> drivers/pci/controller/pci-hyperv.o: In function 'pci_devices_present_work':
> pci-hyperv.c:(.text+0xc02): undefined reference to 'pci_destroy_slot'
> drivers/pci/controller/pci-hyperv.o: In function 'hv_pci_remove':
> pci-hyperv.c:(.text+0xe50): undefined reference to 'pci_destroy_slot'
> drivers/pci/controller/pci-hyperv.o: In function 'hv_eject_device_work':
> pci-hyperv.c:(.text+0x11f9): undefined reference to 'pci_destroy_slot'
> 
> Select SYSFS while PCI_HYPERV is set to fix this.
> 

I'm wondering if is the right way to fix the problem.  Conceptually
is it possible to setup & operate virtual PCI devices like 
pci-hyperv.c does, even if sysfs is not present?  Or is it right to
always required sysfs?

The function pci_dev_assign_slot() in slot.c has a null implementation
in include/linux/pci.h when CONFIG_SYSFS is not defined, which
seems to be trying to solve the same problem for that function.  And
if CONFIG_HOTPLUG_PCI is defined but CONFIG_SYSFS is not,
pci_hp_create_module_link() and pci_hp_remove_module_link()
look like they would have the same problem.  Maybe there should
be degenerate implementations of pci_create_slot() and
pci_destroy_slot() for cases when CONFIG_SYSFS is not defined?

But I'll admit I don't know the full story behind how PCI slots
are represented and used, so maybe I'm off base.  I just noticed
the inconsistency in how other functions in slot.c are handled.

Thoughts?

Michael