linux-kernel - Re: [PATCH/RFC 1/2] init/initramfs.c: allow asynchronous unpacking

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Date:   Wed, 24 Feb 2021 23:13:02 +0100
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jonathan Corbet <corbet@....net>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH/RFC 1/2] init/initramfs.c: allow asynchronous unpacking

On 24/02/2021 18.17, Linus Torvalds wrote:
> On Wed, Feb 24, 2021 at 6:29 AM Rasmus Villemoes
> <linux@...musvillemoes.dk> wrote:
>>
>> So add an initramfs_async= kernel parameter, allowing the main init
>> process to proceed to handling device_initcall()s without waiting for
>> populate_rootfs() to finish.
> 
> Hmm. This is why we have the whole "async_schedule()" thing (mostly
> used for things like disk spin-up etc). Is there some reason you
> didn't use that infrastructure?

Mostly because I completely forgot it existed, it's not an API you
stumble upon in every other source file.

I guess I could use that, but it would look very much like what I have
now - there'd still be some function to call to make sure the initramfs
is ready, only that would then do async_synchronize() instead of
wait_for_completion().

Is there some fundamental reason something like this shouldn't be
doable? Are there places other than the usermodehelper and firmware
loading (and obviously right-before-opening /dev/console and exec'ing
/init) that would need to be taught about this?

Rasmus