Re: [PATCH v2 2/2] modules: add CONFIG_MODPROBE_PATH

[Jessica Yu]

+++ 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@xxxxxxxxxxxxxxxxxx>

Acked-by: Jessica Yu <jeyu@xxxxxxxxxx>

Thanks!