[RFC][PATCH] init: Open /dev/console from rootfs

From: Eric W. Biederman
Date: Wed Mar 03 2010 - 02:53:34 EST

To avoid potential problems with an empty /dev open /dev/console
from rootfs instead of waiting to mount our root filesystem and
mounting it there. This effectively guarantees that there will
be a device node, and it won't be on a filesystem that we will
ever unmount, so there are no issues with leaving /dev/console
open and pinning the filesystem.

This is actually more effective than automatically mounting
devtmpfs on /dev because it removes removes the occasionally
problematic assumption that /dev/console exists from the boot

With this patch I was able to throw busybox on my /boot partition
(which has no /dev directory) and boot into userspace without

The only possible negative consequence I can think of is that
someone out there deliberately used did not use a character device
that is major 5 minor 2 for /dev/console. Does anyone know of a
situation in which that could make sense?

Signed-off-by: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
init/do_mounts_initrd.c | 4 ----
init/main.c | 11 ++++++-----
2 files changed, 6 insertions(+), 9 deletions(-)

diff --git a/init/do_mounts_initrd.c b/init/do_mounts_initrd.c
index 614241b..2b10853 100644
--- a/init/do_mounts_initrd.c
+++ b/init/do_mounts_initrd.c
@@ -30,11 +30,7 @@ static int __init do_linuxrc(void * shell)
extern char * envp_init[];

- sys_close(0);sys_close(1);sys_close(2);
- (void) sys_open("/dev/console",O_RDWR,0);
- (void) sys_dup(0);
- (void) sys_dup(0);
return kernel_execve(shell, argv, envp_init);

diff --git a/init/main.c b/init/main.c
index 67e40fc..9ba505f 100644
--- a/init/main.c
+++ b/init/main.c
@@ -806,11 +806,6 @@ static noinline int init_post(void)
system_state = SYSTEM_RUNNING;

- if (sys_open((const char __user *) "/dev/console", O_RDWR, 0) < 0)
- printk(KERN_WARNING "Warning: unable to open an initial console.\n");
- (void) sys_dup(0);
- (void) sys_dup(0);

current->signal->flags |= SIGNAL_UNKILLABLE;

@@ -864,6 +859,12 @@ static int __init kernel_init(void * unused)


+ /* Open the /dev/console on the rootfs, this should never fail */
+ if (sys_open((const char __user *) "/dev/console", O_RDWR, 0) < 0)
+ printk(KERN_WARNING "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

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