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

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Date:   Sat, 15 Jun 2019 14:18:35 +0800
From:   Yuehaibing <yuehaibing@...wei.com>
To:     Michael Kelley <mikelley@...rosoft.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


On 2019/6/2 6:59, Michael Kelley wrote:
> 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?

268a03a42d33 ("PCI: drivers/pci/slot.c should depend on CONFIG_SYSFS")

make slot.o depends CONFIG_SYSFS

commit 268a03a42d3377d5fb41e6e7cbdec4e0b65cab2e
Author: Alex Chiang <achiang@...com>
Date:   Wed Jun 17 19:03:57 2009 -0600

    PCI: drivers/pci/slot.c should depend on CONFIG_SYSFS

    There is no way to interact with a physical PCI slot without
    sysfs, so encode the dependency and prevent this build error:

        drivers/pci/slot.c: In function 'pci_hp_create_module_link':
        drivers/pci/slot.c:327: error: 'module_kset' undeclared

    This patch _should_ make pci-sysfs.o depend on CONFIG_SYSFS too,
    but we cannot (yet) because the PCI core merrily assumes the
    existence of sysfs:

        drivers/built-in.o: In function `pci_bus_add_device':
        drivers/pci/bus.c:89: undefined reference to `pci_create_sysfs_dev_files'
        drivers/built-in.o: In function `pci_stop_dev':
        drivers/pci/remove.c:24: undefined reference to `pci_remove_sysfs_dev_files'

    So do the minimal bit for now and figure out how to untangle it
    later.

If No CONFIG_SYSFS, slot.o is not build

> 
> Michael
> 
>