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

[Janne Huttunen]

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.