linux-kernel - Re: [PATCH v4] powerpc/pseries: read the lpar name from the firmware

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Message-ID: <ac208963-d334-1f46-0db2-4a8d073b2963@linux.ibm.com>
Date:   Wed, 5 Jan 2022 17:17:21 -0800
From:   Tyrel Datwyler <tyreld@...ux.ibm.com>
To:     Nathan Lynch <nathanl@...ux.ibm.com>,
        Laurent Dufour <ldufour@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] powerpc/pseries: read the lpar name from the firmware

On 1/5/22 3:19 PM, Nathan Lynch wrote:
> Laurent Dufour <ldufour@...ux.ibm.com> writes:
>> On 07/12/2021, 18:11:09, Laurent Dufour wrote:
>>> The LPAR name may be changed after the LPAR has been started in the HMC.
>>> In that case lparstat command is not reporting the updated value because it
>>> reads it from the device tree which is read at boot time.
>>>
>>> However this value could be read from RTAS.
>>>
>>> Adding this value in the /proc/powerpc/lparcfg output allows to read the
>>> updated value.
>>
>> Do you consider taking that patch soon?
> 
> This version prints an error on non-PowerVM guests the first time
> lparcfg is read.

I assume because QEMU doesn't implement the LPAR_NAME token for get_sysparm.

> 
> And I still contend that having this function fall back to reporting the
> partition name in the DT would provide a beneficial consistency in the
> user-facing API, allowing programs to avoid hypervisor-specific branches
> in their code. 

Agreed, if the get_sysparm fails just report the lpar-name from the device tree.

I don't understand the resistance I've encountered here.
> The fallback I'm suggesting (a root node property lookup) is certainly
> not more complex than the RTAS call sequence you've already implemented.
> 

Is there benefit of adding a partition_name field/value pair to lparcfg? The
lparstat utility can just as easily make the get_sysparm call via librtas.
Further, rtas_filters allows this particular RTAS call from userspace.

-Tyrel