linux-kernel - Re: [PATCH pci-next v1 0/1] PCI/sysfs: Expose PCIe device serial number

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Message-ID: <20250716102327.00004dd7@huawei.com>
Date: Wed, 16 Jul 2025 10:23:27 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Matthew Wood <thepacketgeek@...il.com>
CC: Bjorn Helgaas <bhelgaas@...gle.com>, <linux-pci@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH pci-next v1 0/1] PCI/sysfs: Expose PCIe device serial
 number

On Tue, 15 Jul 2025 08:59:42 -0700
Matthew Wood <thepacketgeek@...il.com> wrote:

> On Tue, Jul 15, 2025 at 4:19 AM Jonathan Cameron
> <Jonathan.Cameron@...wei.com> wrote:
> >
> > On Sat, 12 Jul 2025 18:17:12 -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 2-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:cc:00.0/device_serial_number
> > >     00-80-ee-00-00-00-41-80
> > >  
> >
> > What is the use case for this? I can think of some possibilities but good to
> > see why you care here.  
> 
> Two primary use cases we have are for inventory tooling and health
> check tooling; being able to
> reliably collect device serial numbers for tracking unique devices
> whose BDFs could change is
> critical. Sometimes in the process of hardware troubleshooting, cards
> are swapped and BDF idents
> change but we want to track devices by serial number without possibly
> fragile regexps.

Ok.  So you want to avoid having pull this from lspci output which
makes sense to me. Not sure what Bjorn and others think about this
though.


> 
> >
> >  
> > > Accompanying lspci output:
> > >
> > >     sudo lspci -vvv -s cc:00.0
> > >         cc: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
> > >             ...
> > >
> > > If a device doesn't support the serial number capability, userspace will receive
> > > an empty read:  
> >
> > Better if possible to not expose the sysfs attribute if no such capability.
> > We already have pcie_dev_attrs_are_visible() so easy to extend that.  
> 
> That's a great point, it looks like I could match on the attribute
> name to specifically hide device_serial_number
> if the device does not support the cap, but I can't find any precedent
> for matching on a->name in pci-sysfs.c.
> Would something like this be alright after the check for pci_is_pcie(dev):
> 
>     if (a->name == "device_serial_number") {
>         // check if device has serial, if not return 0
>     }

if (a == &dev_attr_device_serial_number.attr)
or something like that.

No need for string matching.

Jonathan


> 
> >
> >  
> > >
> > >     more /sys/devices/pci0000:00/0000:00:07.1/device_serial_number
> > >     echo $?
> > >     0
> > >
> > >
> > > Matthew Wood (1):
> > >   PCI/sysfs: Expose PCIe device serial number
> > >
> > >  drivers/pci/pci-sysfs.c | 17 +++++++++++++++++
> > >  1 file changed, 17 insertions(+)
> > >  
> >