Hi Bjorn, Hi Kernel Hackers, With the below patch I'm proposing to expose a global (i.e. not device bound) runtime attribute of the s390 PCI implementation (zPCI) called "UID Checking". You can find some background information on what this attribute means and why it is important at the end of this mail. The reason I'm writing to you about it however is that this is the first global PCI attribute we would like to expose to user space and I'm searching for a good place to put it. The proposed patch uses "/sys/bus/pci/zpci/uid_checking" which from our perspective would be a great choice but I realize that there currently are no platform specific attributes directly under "/sys/bus/pci" so this clearly requires some discussion. What's your thought on this and do you know of any other platform specific global PCI attributes as I couldn't find any?
Best regards, Niklas Schnelle Background: On s390 OSs always run under at least a machine level hypervisor (LPAR). Simpliefied by usually running from SAN this makes VM migration possible at every level. For PCI this has created the need to allow PCI IDs to be stable across machines and to be partly user defined such that the setup of an existing VM on one machine can be recreated on another machine. In particular the Domain part of the PCI ID can be user defined by setting a per device value called UID. Since this was a late addition and isn't used by all OSs and since UIDs need to be unique if used as Domains, there is an additional global platform supplied runtime value called "UID Checking". This value indicates if UIDs are guaranteed to be unique and set which triggers Linux to use the UIDs as PCI Domains otherwise PCI Domains are simply incremented as necessary. This "UID Checking" setting is thus very important e.g. when deciding how network interface names are generated as it indicates if the domain part of the PCI ID will remain stable across reboots and migrations. Once exposed we will propose a patch to udev/systemd to use the "UID Checking" attribute to prefer network interface names which can be guaranteed to be stable and re-creatable for migration. Niklas Schnelle (1): s390/pci: expose UID checking state in sysfs Documentation/ABI/testing/sysfs-bus-pci | 11 ++++++++ arch/s390/include/asm/pci.h | 3 +++ arch/s390/pci/pci.c | 4 +++ arch/s390/pci/pci_sysfs.c | 34 +++++++++++++++++++++++++ 4 files changed, 52 insertions(+) -- 2.17.1
