linux-kernel - Re: [PATCH] PCI: export pci device assignment info as read only via sysfs

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Date:	Tue, 30 Dec 2014 08:51:14 -0500 (EST)
From:	Alex Williamson <alex.williamson@...hat.com>
To:	Ethan Zhao <ethan.zhao@...cle.com>
Cc:	bhelgaas@...gle.com, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, ethan kernel <ethan.kernel@...il.com>
Subject: Re: [PATCH] PCI: export pci device assignment info as read only via
 sysfs



----- Original Message -----
> This patch exports assignment flag of PCI device via sysfs, so user
> space application could know if PCI device was assigned to guest OS
> or not via interface as following from viewpoint of host device
> management:
> 
>  PCI device was assigned to guest OS
>  $cat /sys/devices/pci0000:00/0000:00:1f.3/assigned
>  1
> 
>  PCI device isn't assigned to guest OS
>  $cat /sys/devices/pci0000:00/0000:00:1f.3/assigned
>  0
> 
> Compiled and tested with v3.18.1
> 
> Signed-off-by: Ethan Zhao <ethan.zhao@...cle.com>
> ---
>  drivers/pci/pci-sysfs.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> index 2c6643f..0ac3780 100644
> --- a/drivers/pci/pci-sysfs.c
> +++ b/drivers/pci/pci-sysfs.c
> @@ -547,6 +547,15 @@ static ssize_t driver_override_show(struct device *dev,
>  }
>  static DEVICE_ATTR_RW(driver_override);
>  
> +static ssize_t assigned_show(struct device *dev, struct device_attribute
> *attr,
> +			 char *buf)
> +{
> +	struct pci_dev *pdev = to_pci_dev(dev);
> +
> +	return sprintf(buf, "%d\n", pci_is_dev_assigned(pdev) ? 1 : 0);
> +}
> +static DEVICE_ATTR_RO(assigned);
> +
>  static struct attribute *pci_dev_attrs[] = {
>  	&dev_attr_resource.attr,
>  	&dev_attr_vendor.attr,
> @@ -573,6 +582,7 @@ static struct attribute *pci_dev_attrs[] = {
>  	&dev_attr_devspec.attr,
>  #endif
>  	&dev_attr_driver_override.attr,
> +	&dev_attr_assigned.attr,
>  	NULL,
>  };
>  

NAK.  The assigned attribute of a device is already in contention, it's racy and not universally used.  If we can't even make it a consistent and reliable internal interface, we certainly shouldn't be exposing it to userspace.  Thanks,

Alex
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