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Re: [Qemu-devel] [RFC][PATCH 0/6] "bootonceindex" property

From: Laszlo Ersek
Subject: Re: [Qemu-devel] [RFC][PATCH 0/6] "bootonceindex" property
Date: Thu, 23 Mar 2017 10:13:36 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0

On 03/23/17 07:53, Janne Huttunen wrote:
> On Wed, 2017-03-22 at 16:29 +0100, Laszlo Ersek wrote:
>>> I'm not. I'm using QMP to change the index dynamically.
>> Wait, if you are already changing the "bootindex" property
>> dynamically (do I understand that right?)
> No, I'm not changing "bootindex" dynamically. I'm changing
> "bootonceindex" dynamically. The point is that whatever
> change I'm making is supposed to affect only one boot, the
> next one. Since the guest can trigger reboots by itself,
> I don't necessarily know when they are going to happen.
> Like I said earlier, I can get very close to the semantics
> I need if set the "bootindex" and get an event when the
> boot happens so that I know when to reset the bootindex
> back to the original value. However doing it like that
> is (at least in theory) racy if the event isn't synchronous
> and it requires some process that actively monitors those
> events which I'm trying to avoid.
>> ...and it could have a significant maintenance footprint,
>> while the feature does look niche (to me anyway).
> Whatever I'm currently doing is definitely a niche, but very
> similar setting of a one time boot source while the system
> is running is e.g. part of the IPMI standard (see "Set
> System Boot Options Command" in IPMI Specification), so
> the concept itself is not that much of a niche.

... Okay, I've spoken my mind on this, and have nothing more to add. I'm
still not convinced, but that doesn't mean you can't convince others.
(And you need to convince others more than me, because I'm not a QEMU
maintainer -- I just wanted to voice my opinion, since this was an RFC.)

What really matters to me though is that the "bootorder" fw_cfg file
- both its current, exclusive role, for communicating the boot order to
the firmware,
- and its syntax & semantics.


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