Laurent Dufour <lduf...@linux.ibm.com> writes: > On 07/12/2021, 18:07:50, Nathan Lynch wrote: >> Laurent Dufour <lduf...@linux.ibm.com> writes: >>> On 07/12/2021, 15:32:39, Nathan Lynch wrote: >>>> Is there a reasonable fallback for VMs where this parameter doesn't >>>> exist? PowerVM partitions should always have it, but what do we want the >>>> behavior to be on other hypervisors? >>> >>> In that case, there is no value displayed in the /proc/powerpc/lparcfg and >>> the lparstat -i command will fall back to the device tree value. I can't >>> see any valid reason to report the value defined in the device tree >>> here. >> >> Here's a valid reason :-) >> >> lparstat isn't the only possible consumer of the interface, and the >> 'ibm,partition-name' property and the dynamic system parameter clearly >> serve a common purpose. 'ibm,partition-name' is provided by qemu. > > If the hypervisor is not providing this value, this is not the goal of this > interface to fetch it from the device tree. > > Any consumer should be able to fall back on the device tree value, and > there is no added value to do such a trick in the kernel when it can be > done in the user space.
There is value in imposing a level of abstraction so that the semantics are: * Report the name assigned to the guest by the hosting environment, if available as opposed to * Return the string returned by a RTAS call to ibm,get-system-parameter with token 55, if implemented The benefit is that consumers of lparcfg do not have to be coded with the knowledge that "if a partition_name= line is absent, the ibm,get-system-parameter RTAS call must have failed, so now I should read /sys/firmware/devicetree/base/ibm,partition_name." That's the sort of esoterica that is appropriate for the kernel to encapsulate. And I'd say the effort involved (falling back to a root node property lookup) is proportional to the benefit.
