linux-kernel - Re: [PATCH v6 1/1] PCI/sysfs: Expose PCIe device serial number

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Message-ID: <20250721105302.0000618d@huawei.com>
Date: Mon, 21 Jul 2025 10:53:02 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Matthew Wood <thepacketgeek@...il.com>
CC: Bjorn Helgaas <bhelgaas@...gle.com>, Mario Limonciello
	<superm1@...nel.org>, Thomas Weißschuh
	<thomas.weissschuh@...utronix.de>, <linux-kernel@...r.kernel.org>,
	<linux-pci@...r.kernel.org>
Subject: Re: [PATCH v6 1/1] PCI/sysfs: Expose PCIe device serial number

On Fri, 18 Jul 2025 12:32:29 -0700
Matthew Wood <thepacketgeek@...il.com> 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 serial_number sysfs attribute will not be visible.
> 
> Signed-off-by: Matthew Wood <thepacketgeek@...il.com>
> Reviewed-by: Mario Limonciello <superm1@...nel.org>

Nice. The %8phD that Thomas pointed out was new to me. Very useful!

Reviewed-by: Jonathan Cameron <jonathan.cameron@...wei.com>


> ---
>  Documentation/ABI/testing/sysfs-bus-pci |  9 +++++++++
>  drivers/pci/pci-sysfs.c                 | 27 ++++++++++++++++++++++---
>  2 files changed, 33 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci
> index 69f952fffec7..0a2580cdd58c 100644
> --- a/Documentation/ABI/testing/sysfs-bus-pci
> +++ b/Documentation/ABI/testing/sysfs-bus-pci
> @@ -612,3 +612,12 @@ Description:
>  
>  		  # ls doe_features
>  		  0001:01        0001:02        doe_discovery
> +
> +What:		/sys/bus/pci/devices/.../serial_number
> +Date:		October 2025
> +Contact:	Matthew Wood <thepacketgeek@...il.com>
> +Description:
> +		This is visible only for PCIe devices that support the serial
> +		number extended capability. The file is read only and due to
> +		the possible sensitivity of accessible serial numbers, admin
> +		only.
> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> index 268c69daa4d5..1d26e4336f1b 100644
> --- a/drivers/pci/pci-sysfs.c
> +++ b/drivers/pci/pci-sysfs.c
> @@ -30,6 +30,7 @@
>  #include <linux/msi.h>
>  #include <linux/of.h>
>  #include <linux/aperture.h>
> +#include <linux/unaligned.h>
>  #include "pci.h"
>  
>  #ifndef ARCH_PCI_DEV_GROUPS
> @@ -239,6 +240,22 @@ static ssize_t current_link_width_show(struct device *dev,
>  }
>  static DEVICE_ATTR_RO(current_link_width);
>  
> +static ssize_t serial_number_show(struct device *dev,
> +				  struct device_attribute *attr, char *buf)
> +{
> +	struct pci_dev *pci_dev = to_pci_dev(dev);
> +	u64 dsn;
> +	u8 bytes[8];
> +
> +	dsn = pci_get_dsn(pci_dev);
> +	if (!dsn)
> +		return -EIO;
> +	put_unaligned_be64(dsn, bytes);
> +
> +	return sysfs_emit(buf, "%8phD\n", bytes);
> +}
> +static DEVICE_ATTR_ADMIN_RO(serial_number);
> +
>  static ssize_t secondary_bus_number_show(struct device *dev,
>  					 struct device_attribute *attr,
>  					 char *buf)
> @@ -660,6 +677,7 @@ 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_serial_number.attr,
>  	NULL,
>  };
>  
> @@ -1749,10 +1767,13 @@ 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;
>  
> -	return 0;
> +	if (a == &dev_attr_serial_number.attr && !pci_get_dsn(pdev))
> +		return 0;
> +
> +	return a->mode;
>  }
>  
>  static const struct attribute_group pci_dev_group = {