path: root/init
diff options
authorRasmus Villemoes <linux@rasmusvillemoes.dk>2021-05-06 18:05:45 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2021-05-07 00:26:33 -0700
commit17652f4240f7a501ecc13e9fdb06982569cde51f (patch)
treecd38179213e285a9d2c9bbaeb7106f181362c397 /init
parente7cb072eb988e46295512617c39d004f9e1c26f8 (diff)
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 made the initramfs unpacking asynchronous - 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. Link: https://lkml.kernel.org/r/20210313212528.2956377-3-linux@rasmusvillemoes.dk Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Acked-by: Jessica Yu <jeyu@kernel.org> Acked-by: Luis Chamberlain <mcgrof@kernel.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Nick Desaulniers <ndesaulniers@google.com> Cc: Takashi Iwai <tiwai@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'init')
1 files changed, 12 insertions, 0 deletions
diff --git a/init/Kconfig b/init/Kconfig
index 1413413fcb9f..d83cb634c24f 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -2299,6 +2299,18 @@ config MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS
If unsure, say N.
+ string "Path to modprobe binary"
+ default "/sbin/modprobe"
+ help
+ When kernel code requests a module, it does so by calling
+ the "modprobe" userspace utility. This option allows you to
+ set the path where that binary is found. This can be changed
+ at runtime via the sysctl file
+ /proc/sys/kernel/modprobe. Setting this to the empty string
+ removes the kernel's ability to request modules (but
+ userspace can still load modules explicitly).
bool "Trim unused exported kernel symbols" if EXPERT
depends on !COMPILE_TEST

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