linux-kernel - Re: [PATCH v2 2/2] modules: add CONFIG_MODPROBE

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Date:   Thu, 11 Mar 2021 14:28:14 +0100
From:   Jessica Yu <jeyu@...nel.org>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     Luis Chamberlain <mcgrof@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Borislav Petkov <bp@...en8.de>,
        Jonathan Corbet <corbet@....net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH v2 2/2] modules: add CONFIG_MODPROBE_PATH

+++ Rasmus Villemoes [09/03/21 22:17 +0100]:
>Allow the developer to specifiy the initial value of the
>modprobe_path[] string. This can be used to set it to the empty string
>initially, thus effectively disabling request_module() during early
>boot until userspace writes a new value via the
>/proc/sys/kernel/modprobe interface. [1]
>
>When building a custom kernel (often for an embedded target), it's
>normal to build everything into the kernel that is needed for booting,
>and indeed the initramfs often contains no modules at all, so every
>such request_module() done before userspace init has mounted the real
>rootfs is a waste of time.
>
>This is particularly useful when combined with the previous patch,
>which allowed the initramfs to be unpacked asynchronously - for that
>to work, it had to make any usermodehelper call wait for the unpacking
>to finish before attempting to invoke the userspace helper. By
>eliminating all such (known-to-be-futile) calls of usermodehelper, the
>initramfs unpacking and the {device,late}_initcalls can proceed in
>parallel for much longer.
>
>For a relatively slow ppc board I'm working on, the two patches
>combined lead to 0.2s faster boot - but more importantly, the fact
>that the initramfs unpacking proceeds completely in the background
>while devices get probed means I get to handle the gpio watchdog in
>time without getting reset.
>
>[1] __request_module() already has an early -ENOENT return when
>modprobe_path is the empty string.
>
>Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>

Acked-by: Jessica Yu <jeyu@...nel.org>

Thanks!