linux-kernel - Re: [REGRESSION] Re: [PATCH] Revert "vmgenid: emit uevent when VMGENID updates"

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Date: Fri, 26 Apr 2024 15:43:51 +0200
From: Babis Chalios <bchalios@...zon.es>
To: "Jason A. Donenfeld" <Jason@...c4.com>, Alexander Graf <graf@...zon.com>
CC: Lennart Poettering <mzxreary@...inter.de>, <linux-kernel@...r.kernel.org>,
	<stable@...r.kernel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>, Theodore Ts'o
	<tytso@....edu>, "Cali, Marco" <xmarcalx@...zon.co.uk>, Arnd Bergmann
	<arnd@...db.de>, "rostedt@...dmis.org" <rostedt@...dmis.org>, "Christian
 Brauner" <brauner@...nel.org>, <linux@...mhuis.info>,
	<regressions@...ts.linux.dev>
Subject: Re: [REGRESSION] Re: [PATCH] Revert "vmgenid: emit uevent when VMGENID
 updates"

Hi Jason,

On 4/26/24 14:52, Jason A. Donenfeld wrote:
> I don't think adding UAPI to an individual device driver like this is a
> good approach especially considering that the virtio changes we
> discussed some time ago will likely augment this and create another
> means of a similar notification. And given that this intersects with
> other userspace-oriented work I hope to get back to pretty soon, I think
> introducing some adhoc mechanism like this adds clutter and isn't the
> ideal way forward.
>

Correct me if I'm wrong, but the virtio changes were meant to mean "please
reseed your PRNGs". That's why we wanted to route them via random.c. We
designed them specifically so that virtio-rng would be only one of the 
potential
systems that would emit such notifications, whereas other systems might have
nothing to do with VM events.

With that in mind, could you describe how these events would be useful 
to the
use case of Lennart? systemd does not need a notification every time the 
system
believes PRNGs need to be reseeded. It explicitly needs a notification 
when a VM
was cloned. This has nothing to do with PRNGs and I don't believe random.c,
virtio-rng, or vgetrand() should be responsible for delivering this.

Cheers,
Babis