linux-kernel - [PATCH v2 0/2] background initramfs unpacking, and CONFIG_MODPROBE

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Message-Id: <20210309211700.2011017-1-linux@rasmusvillemoes.dk>
Date:   Tue,  9 Mar 2021 22:16:58 +0100
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Luis Chamberlain <mcgrof@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Jessica Yu <jeyu@...nel.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>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: [PATCH v2 0/2] background initramfs unpacking, and CONFIG_MODPROBE_PATH

These two patches are independent, but better-together.

The second is a rather trivial patch that simply allows the developer
to change "/sbin/modprobe" to something else - e.g. the empty string,
so that all request_module() during early boot return -ENOENT early,
without even spawning a usermode helper.

The first patch allows delegating decompressing the initramfs to a
worker thread, allowing do_initcalls() in main.c to proceed to the
device_ and late_ initcalls without waiting for that decompression
(and populating of rootfs) to finish. Obviously, some of those later
calls may rely on the initramfs being available, so I've added
synchronization points in the firmware loader and usermodehelper paths
- there might be other places that would need this.

There's not much to win if most of the functionality needed during
boot is only available as modules. But systems with a custom-made
.config and initramfs can boot faster, partly due to utilizing more
than one cpu earlier, partly by avoiding known-futile modprobe calls
(which would still trigger synchronization with the initramfs
unpacking, thus eliminating most of the first benefit).

Routing-wise, I hope akpm can handle both patches. Andrew, Luis?

Changes in v2:

- Rebase on master, piggy-backing on the include guard and #ifdef
  CONFIG_BLK_DEV_INITRD added to initrd.h in fade5cad93 and
  c72160fe05.

- Use existing async_* API instead of wait_for_completion/complete_all

- Drop debug leftovers from wait_for_initramfs().

- Fix initialization of initramfs_async variable.

Rasmus Villemoes (2):
  init/initramfs.c: allow asynchronous unpacking
  modules: add CONFIG_MODPROBE_PATH

 .../admin-guide/kernel-parameters.txt         | 12 ++++++
 drivers/base/firmware_loader/main.c           |  2 +
 include/linux/initrd.h                        |  2 +
 init/Kconfig                                  | 12 ++++++
 init/initramfs.c                              | 41 ++++++++++++++++++-
 init/main.c                                   |  1 +
 kernel/kmod.c                                 |  2 +-
 kernel/umh.c                                  |  2 +
 usr/Kconfig                                   | 10 +++++
 9 files changed, 82 insertions(+), 2 deletions(-)

-- 
2.29.2