[PATCH v5 0/1] PCI/sysfs: Expose PCIe device serial number

[PATCH v5 0/1] PCI/sysfs: Expose PCIe device serial number

[Matthew Wood]

Add a single sysfs read-only, admin-only interface for reading PCIe device
serial numbers from userspace, using the same hexadecimal 1-byte dashed
formatting as lspci serial number capability output:

    more /sys/devices/pci0000:c0/0000:c0:01.1/0000:c1:00.0/0000:c2:1f.0/0000:ef:00.0/serial_number
    00-80-ee-00-00-00-41-80

If a device doesn't support the serial number capability, the
serial_number sysfs attribute will not be visible.

Comparing serial number format to lspci output:

    sudo lspci -vvv -s ef:00.0
        ef:00.0 Serial Attached SCSI controller: Broadcom / LSI PCIe Switch management endpoint (rev b0)
            Subsystem: Broadcom / LSI Device 0144
            ...
            Capabilities: [100 v1] Device Serial Number 00-80-ee-00-00-00-41-80
            ...

This PCIe device sysfs attribute eliminates the need for parsing lspci
output (e.g. regexp) for userspace applications that utilize serial
numbers.


Matthew Wood (1):
  PCI/sysfs: Expose PCIe device serial number

 Documentation/ABI/testing/sysfs-bus-pci |  9 +++++++++
 drivers/pci/pci-sysfs.c                 | 26 ++++++++++++++++++++++---
 2 files changed, 32 insertions(+), 3 deletions(-)

-- 
2.50.0

[PATCH v5 1/1] PCI/sysfs: Expose PCIe device serial number

[Matthew Wood]

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@gmail.com>
Reviewed-by: Mario Limonciello <superm1@kernel.org>
---
 Documentation/ABI/testing/sysfs-bus-pci |  9 +++++++++
 drivers/pci/pci-sysfs.c                 | 26 ++++++++++++++++++++++---
 2 files changed, 32 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@gmail.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..bc0e0add15d1 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 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_ADMIN_RO(serial_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_serial_number.attr,
 	NULL,
 };
 
@@ -1749,10 +1766,13 @@ 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 = {
-- 
2.50.0

Re: [PATCH v5 1/1] PCI/sysfs: Expose PCIe device serial number

[Jonathan Cameron]

On Thu, 17 Jul 2025 09:50:54 -0700
Matthew Wood <thepacketgeek@gmail.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@gmail.com>
> Reviewed-by: Mario Limonciello <superm1@kernel.org>
Hi Matthew,

A suggestion inline.  I'm also fine with the current version if that's
what people feel more comfortable with.

If we stick to what you have here
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>

Jonathan

> ---
>  Documentation/ABI/testing/sysfs-bus-pci |  9 +++++++++
>  drivers/pci/pci-sysfs.c                 | 26 ++++++++++++++++++++++---
>  2 files changed, 32 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@gmail.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..bc0e0add15d1 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 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);

I wonder if doing the following i too esoteric. Eyeballing those shifts is painful.

	u8 bytewise[8]; /* naming hard... */

	put_unaligned_u64(dsn, bytewise);

	return sysfs_emit(buf, "%02x-%02x-%02x-%02x-%02x-%02x-%02x-%02x\n",
		bytewise[0], bytewise[1], bytewise[2], bytewise[3],
		bytewise[4], bytewise[5], bytewise[6], bytewise[7]);


> +}
> +static DEVICE_ATTR_ADMIN_RO(serial_number);

Re: [PATCH v5 1/1] PCI/sysfs: Expose PCIe device serial number

[Thomas Weißschuh]

On Fri, Jul 18, 2025 at 11:36:11AM +0100, Jonathan Cameron wrote:
> On Thu, 17 Jul 2025 09:50:54 -0700
> Matthew Wood <thepacketgeek@gmail.com> wrote:

(...)

> > diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> > index 268c69daa4d5..bc0e0add15d1 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 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);
> 
> I wonder if doing the following i too esoteric. Eyeballing those shifts is painful.
> 
> 	u8 bytewise[8]; /* naming hard... */
> 
> 	put_unaligned_u64(dsn, bytewise);
> 
> 	return sysfs_emit(buf, "%02x-%02x-%02x-%02x-%02x-%02x-%02x-%02x\n",
> 		bytewise[0], bytewise[1], bytewise[2], bytewise[3],
> 		bytewise[4], bytewise[5], bytewise[6], bytewise[7]);

This looks endianess-unsafe.

Maybe just do what some drivers are doing:

	u8 bytes[8];

	put_unaligned_be64(dsn, bytes);

	return sysfs_emit(buf, "%8phD");

> 
> 
> > +}
> > +static DEVICE_ATTR_ADMIN_RO(serial_number);
> 
> 

Re: [PATCH v5 1/1] PCI/sysfs: Expose PCIe device serial number

[Matthew Wood]

On Fri, Jul 18, 2025 at 4:02 AM Thomas Weißschuh
<thomas.weissschuh@linutronix.de> wrote:
>
> On Fri, Jul 18, 2025 at 11:36:11AM +0100, Jonathan Cameron wrote:
> > On Thu, 17 Jul 2025 09:50:54 -0700
> > Matthew Wood <thepacketgeek@gmail.com> wrote:
>
> (...)
>
> > > diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> > > index 268c69daa4d5..bc0e0add15d1 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 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);
> >
> > I wonder if doing the following i too esoteric. Eyeballing those shifts is painful.
> >
> >       u8 bytewise[8]; /* naming hard... */
> >
> >       put_unaligned_u64(dsn, bytewise);
> >
> >       return sysfs_emit(buf, "%02x-%02x-%02x-%02x-%02x-%02x-%02x-%02x\n",
> >               bytewise[0], bytewise[1], bytewise[2], bytewise[3],
> >               bytewise[4], bytewise[5], bytewise[6], bytewise[7]);
>
> This looks endianess-unsafe.
>
> Maybe just do what some drivers are doing:
>
>         u8 bytes[8];
>
>         put_unaligned_be64(dsn, bytes);
>
>         return sysfs_emit(buf, "%8phD");

Thank you both for your continued review! That reads much nicer, I
should've known to look at how others were doing this formatting. I'll
have a new patch later today.

Re: [PATCH v5 1/1] PCI/sysfs: Expose PCIe device serial number

[Jonathan Cameron]

On Fri, 18 Jul 2025 13:02:00 +0200
Thomas Weißschuh <thomas.weissschuh@linutronix.de> wrote:

> On Fri, Jul 18, 2025 at 11:36:11AM +0100, Jonathan Cameron wrote:
> > On Thu, 17 Jul 2025 09:50:54 -0700
> > Matthew Wood <thepacketgeek@gmail.com> wrote:  
> 
> (...)
> 
> > > diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> > > index 268c69daa4d5..bc0e0add15d1 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 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);  
> > 
> > I wonder if doing the following i too esoteric. Eyeballing those shifts is painful.
> > 
> > 	u8 bytewise[8]; /* naming hard... */
> > 
> > 	put_unaligned_u64(dsn, bytewise);
> > 
> > 	return sysfs_emit(buf, "%02x-%02x-%02x-%02x-%02x-%02x-%02x-%02x\n",
> > 		bytewise[0], bytewise[1], bytewise[2], bytewise[3],
> > 		bytewise[4], bytewise[5], bytewise[6], bytewise[7]);  
> 
> This looks endianess-unsafe.
> 
> Maybe just do what some drivers are doing:
> 
> 	u8 bytes[8];
> 
> 	put_unaligned_be64(dsn, bytes);
Absolutely. Typo :(  I don't think there is a put_unaligned_u64()

> 
> 	return sysfs_emit(buf, "%8phD");
> 
> > 
> >   
> > > +}
> > > +static DEVICE_ATTR_ADMIN_RO(serial_number);  
> > 
> >   
>