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init: Open /dev/console from rootfs

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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
code.

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

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@xmission.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Eric W. Biederman 2010-03-02 23:53:19 -08:00 committed by Al Viro
parent 2329e392ac
commit 2bd3a997be
2 changed files with 6 additions and 9 deletions
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4
init/do_mounts_initrd.c
View file

@ -30,11 +30,7 @@ static int __init do_linuxrc(void * shell)
extern char * envp_init[];
sys_close(old_fd);sys_close(root_fd);
sys_close(0);sys_close(1);sys_close(2);
sys_setsid();
(void) sys_open("/dev/console",O_RDWR,0);
(void) sys_dup(0);
(void) sys_dup(0);
return kernel_execve(shell, argv, envp_init);
}

11
init/main.c
View file

@ -806,11 +806,6 @@ static noinline int init_post(void)
system_state = SYSTEM_RUNNING;
numa_default_policy();
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;
@ -873,6 +868,12 @@ static int __init kernel_init(void * unused)
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)
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