linux-kernel - Re: [PATCH v6 03/30] PCI: Export busn

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Message-ID: <20150311222835.GA1082@google.com>
Date:	Wed, 11 Mar 2015 17:28:35 -0500
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Yijing Wang <wangyijing@...wei.com>
Cc:	Jiang Liu <jiang.liu@...ux.intel.com>, linux-pci@...r.kernel.org,
	Yinghai Lu <yinghai@...nel.org>, linux-kernel@...r.kernel.org,
	Marc Zyngier <marc.zyngier@....com>,
	linux-arm-kernel@...ts.infradead.org,
	Russell King <linux@....linux.org.uk>, x86@...nel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Tony Luck <tony.luck@...el.com>, linux-ia64@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	Guan Xuetao <gxt@...c.pku.edu.cn>, linux-alpha@...r.kernel.org,
	linux-m68k@...ts.linux-m68k.org, Liviu Dudau <liviu@...au.co.uk>,
	Arnd Bergmann <arnd@...db.de>,
	Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: Re: [PATCH v6 03/30] PCI: Export busn_resource to drivers/pci

On Mon, Mar 09, 2015 at 10:34:00AM +0800, Yijing Wang wrote:
> Export out busn_resource. Xen pcifront module need it.
> 
> Signed-off-by: Yijing Wang <wangyijing@...wei.com>
> ---
>  drivers/pci/pci.h   |    2 ++
>  drivers/pci/probe.c |    3 ++-
>  2 files changed, 4 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index 4091f82..eeacab9 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -10,6 +10,8 @@ bool pcie_cap_has_lnkctl(const struct pci_dev *dev);
>  
>  /* Functions internal to the PCI core code */
>  
> +extern struct resource busn_resource;
> +
>  int pci_create_sysfs_dev_files(struct pci_dev *pdev);
>  void pci_remove_sysfs_dev_files(struct pci_dev *pdev);
>  #if !defined(CONFIG_DMI) && !defined(CONFIG_ACPI)
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 8ef0375..b97ea81 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -17,12 +17,13 @@
>  #define CARDBUS_LATENCY_TIMER	176	/* secondary latency timer */
>  #define CARDBUS_RESERVE_BUSNR	3
>  
> -static struct resource busn_resource = {
> +struct resource busn_resource = {
>  	.name	= "PCI busn",
>  	.start	= 0,
>  	.end	= 255,
>  	.flags	= IORESOURCE_BUS,
>  };
> +EXPORT_SYMBOL(busn_resource);

I don't think this is a good idea.  We support multiple PCI domains, and
each domain has its own 0-255 bus number range.  This busn_resource is
only for domain 0 and probably should be handled in arch code instead of
the PCI core.

Right now, I think it's possible to call pci_scan_bus_parented() or
pci_scan_bus() several times for buses in different domains, and they would
all share the same busn_resource, which would cause corruption.

So it's already broken, but I don't want to make it harder to fix by
exporting this stuff.

>  
>  /* Ugh.  Need to stop exporting this to modules. */
>  LIST_HEAD(pci_root_buses);
> -- 
> 1.7.1
> 
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