Re: [PATCH 1/1] s390/pci: expose a PCI device's UID as its index

Bjorn Helgaas
2021-04-14T20:17:59Z

On Mon, Apr 12, 2021 at 03:59:05PM +0200, Niklas Schnelle wrote:
> On s390 each PCI device has a user-defined ID (UID) exposed under
> /sys/bus/pci/devices/<dev>/uid. This ID was designed to serve as the PCI
> device's primary index and to match the device within Linux to the
> device configured in the hypervisor. To serve as a primary identifier
> the UID must be unique within the Linux instance, this is guaranteed by
> the platform if and only if the UID Uniqueness Checking flag is set
> within the CLP List PCI Functions response.
>
> In this sense the UID serves an analogous function as the SMBIOS
> instance number or ACPI index exposed as the "index" respectively
> "acpi_index" device attributes and used by e.g. systemd to set interface
> names. As s390 does not use and will likely never use ACPI nor SMBIOS
> there is no conflict and we can just expose the UID under the "index"
> attribute whenever UID Uniqueness Checking is active and get systemd's
> interface naming support for free.
>
> Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
> Acked-by: Viktor Mihajlovski <mihajlov@linux.ibm.com>

This seems like a nice solution to me.

Acked-by: Bjorn Helgaas <bhelgaas@google.com>

> ---
> Documentation/ABI/testing/sysfs-bus-pci | 11 +++++---
> arch/s390/pci/pci_sysfs.c | 35 +++++++++++++++++++++++++
> 2 files changed, 42 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci
> index 25c9c39770c6..1241b6d11a52 100644
> --- a/Documentation/ABI/testing/sysfs-bus-pci
> +++ b/Documentation/ABI/testing/sysfs-bus-pci
> @@ -195,10 +195,13 @@ What: /sys/bus/pci/devices/.../index
> Date: July 2010
> Contact: Narendra K <narendra_k@dell.com>, linux-bugs@dell.com
> Description:
> - Reading this attribute will provide the firmware
> - given instance (SMBIOS type 41 device type instance) of the
> - PCI device. The attribute will be created only if the firmware
> - has given an instance number to the PCI device.
> + Reading this attribute will provide the firmware given instance
> + number of the PCI device. Depending on the platform this can
> + be for example the SMBIOS type 41 device type instance or the
> + user-defined ID (UID) on s390. The attribute will be created
> + only if the firmware has given an instance number to the PCI
> + device and that number is guaranteed to uniquely identify the
> + device in the system.
> Users:
> Userspace applications interested in knowing the
> firmware assigned device type instance of the PCI
> diff --git a/arch/s390/pci/pci_sysfs.c b/arch/s390/pci/pci_sysfs.c
> index e14d346dafd6..20dbb2058d51 100644
> --- a/arch/s390/pci/pci_sysfs.c
> +++ b/arch/s390/pci/pci_sysfs.c
> @@ -138,6 +138,38 @@ static ssize_t uid_is_unique_show(struct device *dev,
> }
> static DEVICE_ATTR_RO(uid_is_unique);
>
> +#ifndef CONFIG_DMI
> +/* analogous to smbios index */

I think this is smbios_attr_instance, right? Maybe mention that
specifically to make it easier to match these up.

Looks like smbios_attr_instance and the similar ACPI stuff could use
some updating to use the current attribute group infrastructure.

> +static ssize_t index_show(struct device *dev,
> + struct device_attribute *attr, char *buf)
> +{
> + struct zpci_dev *zdev = to_zpci(to_pci_dev(dev));
> + u32 index = ~0;
> +
> + if (zpci_unique_uid)
> + index = zdev->uid;
> +
> + return sysfs_emit(buf, "%u\n", index);
> +}
> +static DEVICE_ATTR_RO(index);
> +
> +static umode_t zpci_unique_uids(struct kobject *kobj,
> + struct attribute *attr, int n)
> +{
> + return zpci_unique_uid ? attr->mode : 0;
> +}
> +
> +static struct attribute *zpci_ident_attrs[] = {
> + &dev_attr_index.attr,
> + NULL,
> +};
> +
> +static struct attribute_group zpci_ident_attr_group = {
> + .attrs = zpci_ident_attrs,
> + .is_visible = zpci_unique_uids,

It's conventional to name these functions *_is_visible() (another
convention that smbios_attr_instance and acpi_attr_index probably
predate).

> +};
> +#endif
> +
> static struct bin_attribute *zpci_bin_attrs[] = {
> &bin_attr_util_string,
> &bin_attr_report_error,
> @@ -179,5 +211,8 @@ static struct attribute_group pfip_attr_group = {
> const struct attribute_group *zpci_attr_groups[] = {
> &zpci_attr_group,
> &pfip_attr_group,
> +#ifndef CONFIG_DMI
> + &zpci_ident_attr_group,
> +#endif
> NULL,
> };
> --
> 2.25.1
>