Re: [PATCH v3 1/1] PCI/sysfs: Expose PCIe device serial number

[Mario Limonciello <superm1@kernel.org>]

On 7/16/25 11:32 AM, Matthew Wood wrote:
> Add a single sysfs read-only interface for reading PCIe device serial
> numbers from userspace in a programmatic way. This device attribute
> uses the same hexadecimal 1-byte dashed formatting as lspci serial number
> capability output. If a device doesn't support the serial number
> capability, the device_serial_number sysfs attribute will not be visible.
> 
> Signed-off-by: Matthew Wood <thepacketgeek@gmail.com>
> ---
>   Documentation/ABI/testing/sysfs-bus-pci |  7 +++++++
>   drivers/pci/pci-sysfs.c                 | 27 ++++++++++++++++++++++---
>   2 files changed, 31 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci
> index 69f952fffec7..f7e84b3a4204 100644
> --- a/Documentation/ABI/testing/sysfs-bus-pci
> +++ b/Documentation/ABI/testing/sysfs-bus-pci
> @@ -612,3 +612,10 @@ Description:
>   
>   		  # ls doe_features
>   		  0001:01        0001:02        doe_discovery
> +
> +What:		/sys/bus/pci/devices/.../device_serial_number
> +Date:		July 2025
> +Contact:	Matthew Wood <thepacketgeek@gmail.com>
> +Description:
> +		This is visible only for PCIe devices that support the serial
> +		number extended capability. The file is read only.
> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> index 268c69daa4d5..b7b52dea6e31 100644
> --- a/drivers/pci/pci-sysfs.c
> +++ b/drivers/pci/pci-sysfs.c
> @@ -239,6 +239,22 @@ static ssize_t current_link_width_show(struct device *dev,
>   }
>   static DEVICE_ATTR_RO(current_link_width);
>   
> +static ssize_t device_serial_number_show(struct device *dev,
> +				       struct device_attribute *attr, char *buf)
> +{
> +	struct pci_dev *pci_dev = to_pci_dev(dev);
> +	u64 dsn;
> +
> +	dsn = pci_get_dsn(pci_dev);
> +	if (!dsn)
> +		return -EIO;
> +
> +	return sysfs_emit(buf, "%02llx-%02llx-%02llx-%02llx-%02llx-%02llx-%02llx-%02llx\n",
> +		dsn >> 56, (dsn >> 48) & 0xff, (dsn >> 40) & 0xff, (dsn >> 32) & 0xff,
> +		(dsn >> 24) & 0xff, (dsn >> 16) & 0xff, (dsn >> 8) & 0xff, dsn & 0xff);
> +}
> +static DEVICE_ATTR_RO(device_serial_number);

The serial number /could/ be considered sensitive information.  I think 
it's better to use DEVICE_ATTR_ADMIN_RO.

Also, as this is a "device" attribute is it really necessary to encode 
the extra word and "number"?

> +
>   static ssize_t secondary_bus_number_show(struct device *dev,
>   					 struct device_attribute *attr,
>   					 char *buf)
> @@ -660,6 +676,7 @@ static struct attribute *pcie_dev_attrs[] = {
>   	&dev_attr_current_link_width.attr,
>   	&dev_attr_max_link_width.attr,
>   	&dev_attr_max_link_speed.attr,
> +	&dev_attr_device_serial_number.attr,
>   	NULL,
>   };
>   
> @@ -1749,10 +1766,14 @@ static umode_t pcie_dev_attrs_are_visible(struct kobject *kobj,
>   	struct device *dev = kobj_to_dev(kobj);
>   	struct pci_dev *pdev = to_pci_dev(dev);
>   
> -	if (pci_is_pcie(pdev))
> -		return a->mode;
> +	if (!pci_is_pcie(pdev))
> +		return 0;
> +
> +	if (a == &dev_attr_device_serial_number.attr && !pci_get_dsn(pdev))
> +		return 0;
> +
> +	return a->mode;
>   
> -	return 0;
>   }
>   
>   static const struct attribute_group pci_dev_group = {