The patch titled
Subject: initramfs: make initramfs honor CONFIG_DEVTMPFS_MOUNT
has been added to the -mm tree. Its filename is
make-initramfs-honor-config_devtmpfs_mount.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/make-initramfs-honor-config_devtmpfs_mount.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/make-initramfs-honor-config_devtmpfs_mount.patch
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------------------------------------------------------
From: Rob Landley <rob@xxxxxxxxxxx>
Subject: initramfs: make initramfs honor CONFIG_DEVTMPFS_MOUNT
Make initramfs honor CONFIG_DEVTMPFS_MOUNT, fixing 2b2af54a5bb6 ("Driver
Core: devtmpfs - kernel-maintained tmpfs-based /dev"), which didn't
bother. Move /dev/console open after devtmpfs mount, and update help
text.
Commit 456eeabab849 in 2005 made gen_initramfs_list (when run with no
arguments) spit out an 'example' config creating /dev and /dev/console.
The kernel accidentally(?) included this for many years when you didn't
specify initramfs contents, and of course grew dependencies on this
/dev/console node in the (often hidden) initramfs. c33df4eaaf41 ("disable
init/initramfs.c") in 2007 explicitly preserved this dependency.
2bd3a997befc ("init: Open /dev/console from rootfs") in 2010 claimed it
"removes the occasionally problematic assumption that /dev/console exists
from the boot code" but actually just moved it later.
But nobody never tested statically linking an initramfs. If you point
CONFIG_INITRAMFS_SOURCE at a directory running the build as a normal user
you _don't_ get a /dev/console (because you can't create it without being
root, and can't use the existing one out of /dev unless you create your
own initramfs list file), in which case init runs with stdin/stdout/stderr
closed and you get no output.
Eric's test case for his 2010 commit referenced above was:
With this patch I was able to throw busybox on my /boot partition
(which has no /dev directory) and boot into userspace without
problems.
But it didn't work pointing CONFIG_INITRAMFS_SOURCE at a directory of the
same files. This provides the "automatically mounting devtmpfs on /dev"
workaround the earlier commit was trying to avoid.
Link: http://lkml.kernel.org/r/21935caf-501d-e97c-5611-5c4af7e0f9ae@xxxxxxxxxxx
Signed-off-by: Rob Landley <rob@xxxxxxxxxxx>
Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
Cc: Jean-Paul Saman <jean-paul.saman@xxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Prarit Bhargava <prarit@xxxxxxxxxx>
Cc: Yang Shi <yang.shi@xxxxxxxxxx>
Cc: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Emese Revfy <re.emese@xxxxxxxxx>
Cc: Petr Mladek <pmladek@xxxxxxxx>
Cc: Fabian Frederick <fabf@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/base/Kconfig | 14 ++++----------
init/main.c | 15 +++++++++------
2 files changed, 13 insertions(+), 16 deletions(-)
diff -puN drivers/base/Kconfig~make-initramfs-honor-config_devtmpfs_mount drivers/base/Kconfig
--- a/drivers/base/Kconfig~make-initramfs-honor-config_devtmpfs_mount
+++ a/drivers/base/Kconfig
@@ -48,16 +48,10 @@ config DEVTMPFS_MOUNT
bool "Automount devtmpfs at /dev, after the kernel mounted the rootfs"
depends on DEVTMPFS
help
- This will instruct the kernel to automatically mount the
- devtmpfs filesystem at /dev, directly after the kernel has
- mounted the root filesystem. The behavior can be overridden
- with the commandline parameter: devtmpfs.mount=0|1.
- This option does not affect initramfs based booting, here
- the devtmpfs filesystem always needs to be mounted manually
- after the rootfs is mounted.
- With this option enabled, it allows to bring up a system in
- rescue mode with init=/bin/sh, even when the /dev directory
- on the rootfs is completely empty.
+ Automatically mount devtmpfs at /dev on the root filesystem, which
+ lets the system to come up in rescue mode with [rd]init=/bin/sh.
+ Override with devtmpfs.mount=0 on the commandline. Initramfs can
+ create a /dev dir as needed, other rootfs needs the mount point.
config STANDALONE
bool "Select only drivers that don't need compile-time external firmware"
diff -puN init/main.c~make-initramfs-honor-config_devtmpfs_mount init/main.c
--- a/init/main.c~make-initramfs-honor-config_devtmpfs_mount
+++ a/init/main.c
@@ -1038,12 +1038,6 @@ static noinline void __init kernel_init_
do_basic_setup();
- /* Open the /dev/console on the rootfs, this should never fail */
- if (sys_open((const char __user *) "/dev/console", O_RDWR, 0) < 0)
- pr_err("Warning: unable to open an initial console.\n");
-
- (void) sys_dup(0);
- (void) sys_dup(0);
/*
* check if there is an early userspace init. If yes, let it do all
* the work
@@ -1055,8 +1049,17 @@ static noinline void __init kernel_init_
if (sys_access((const char __user *) ramdisk_execute_command, 0) != 0) {
ramdisk_execute_command = NULL;
prepare_namespace();
+ } else if (IS_ENABLED(CONFIG_DEVTMPFS_MOUNT)) {
+ sys_mkdir("/dev", 0755);
+ devtmpfs_mount("/dev");
}
+ /* Open the /dev/console on the rootfs, this should never fail */
+ if (sys_open((const char __user *) "/dev/console", O_RDWR, 0) < 0)
+ pr_err("Warning: unable to open an initial console.\n");
+ (void) sys_dup(0);
+ (void) sys_dup(0);
+
/*
* Ok, we have completed the initial bootup, and
* we're essentially up and running. Get rid of the
_
Patches currently in -mm which might be from rob@xxxxxxxxxxx are
teach-initramfs_root_uid-and-initramfs_root_gid-that-1-means-current-user.patch
clarify-help-text-that-compression-applies-to-ramfs-as-well-as-legacy-ramdisk.patch
make-initramfs-honor-config_devtmpfs_mount.patch
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