chroot= as a new kernel parameter

In the short this patch has added a new chroot= kernel parameter which can be used to changing a chroot of an init process before it will has been runed.

hi *real* hackers,

it is a my first post to lkml and I hope that you will have not been ignored me if I have done some incorrect thing.

In the short this patch has added a new chroot= kernel parameter which can be used to changing a chroot of an init process before it will has been runed. I use that for testing variouses distroes without making a separate partition but by copied a new root-fs to a new subdirectory on the my *base* filesystem.

Quoted 9 lines · Pawel Plociennik

hi *real* hackers,

it is a my first post to lkml and I hope that you will have not been ignored me if I have done some incorrect thing.

In the short this patch has added a new chroot= kernel parameter which can be used to changing a chroot of an init process before it will has been runed. I use that for testing variouses distroes without making a separate partition but by copied a new root-fs to a new subdirectory on the my *base* filesystem.

Hi!

Gentoos initrd (build by genkernel) has support for a chrooted boot, the parameter is called subdir=
Maybe other distros have something similar, it's easy to support this with a initrd/initramfs.

Cheers
Stefan

PS: This is my first post to lkml, too :)
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hi *real* hackers,

it is a my first post to lkml and I hope that you will have not been ignored me if I have done some incorrect thing.

In the short this patch has added a new chroot= kernel parameter which can be used to changing a chroot of an init process before it will has been runed. I use that for testing variouses distroes without making a separate partition but by copied a new root-fs to a new subdirectory on the my *base* filesystem.

diff -urp linux-2.6.24-orig/Documentation/kernel-parameters.txt linux-2.6.24/Documentation/kernel-parameters.txt

Documentation/kernel-parameters.txt +2 -0

@@ -381,6 +381,8 @@ and is between 256 and 4096 characters. 
 			Value can be changed at runtime via
 				/selinux/checkreqprot.
 
+	chroot=		[KNL] call chroot() for init proccess.
+
 	clock=		[BUGS=X86-32, HW] gettimeofday clocksource override.
 			[Deprecated]
 			Forces specified clocksource (if available) to be used

diff -urp linux-2.6.24-orig/init/main.c linux-2.6.24/init/main.c

init/main.c +1 -0

@@ -755,8 +755,22 @@ static void __init do_pre_smp_initcalls(
 		spawn_softlockup_task();
 }
 
+static void *chroot_str;

hi *real* hackers,

In the short this patch has added a new chroot= kernel parameter which can be used to changing a chroot of an init process before it will has been runed.

+ if(chroot_str) {
+ if(sys_chroot(chroot_str) < 0)
+ printk("chroot=%s failed\n", chroot_str);
+ else
+ printk("chroot=%s successed\n",chroot_str);
+ }

Wouldn't booting with 'init=/usr/sbin/chroot /path /sbin/init' achieve the same effect?
Haven't tested it, just wondering.

Quoted 2 lines · Guillaume Chazarain

Wouldn't booting with 'init=/usr/sbin/chroot /path /sbin/init' achieve the same effect?

I think that procces which has pid 0 is a special procces

because it
removes a *zombie* procceses so it is good to use a *dedicated* program for it such as a /sbin/init . /usr/sbin/chroot doesn't remove a *zombie* procceses :-(

You mean pid 1, right? ;-)

Sure, but chroot should then exec /sbin/init as per the given kernel command line. And then you run a real init.

I cannot try it as I don't have another distribution installed in a subdirectory, but if you could test it we would quickly know if it works or not.

Quoted 1 line · Guillaume Chazarain

You mean pid 1, right? ;-)

Of course that (my brain has been mistaked) :-(

Quoted 4 lines

Sure, but chroot should then exec /sbin/init as per the given kernel command line. And then you run a real init.

Quoted 4 lines

I cannot try it as I don't have another distribution installed in a subdirectory, but if you could test it we would quickly know if it works or not.

You have right.
I have tested that and it *works* :-)
so I thing that my patch is *unnecessary* now :-(

Quoted 1 line · Pawel Plociennik

so I thing that my patch is *unnecessary* now :-(

Actually I disagree here. This means that if distro in / breaks, you will not be able to boot in ditstro in /foo any more :-(.

init=/working_distro/lib/ld-linux.so.2 --library-path /working_distro/lib /working_distro/usr/sbin/chroot /working_distro/ /sbin/init

Quoted 5 lines

init=/working_distro/lib/ld-linux.so.2 --library-path /working_distro/lib /working_distro/usr/sbin/chroot /working_distro/ /sbin/init

root=<root> init=/working_distro/lib/ld-linux.so.2 --library-path /working_distro/lib working_distro/usr/sbin/chroot /working_distro/ /sbin/init

I think that it is *interestly* hack but I am not sure that it will be an usable method for all of a distroes which exists on the world. At last my patch is as simple as possible and it has *only* a *few lines of the code* and it can be used
as *independent* method to various *hundred* distroes.

root=<root> chroot=<chroot>

and it looks *beautiful* I think :-)

so I have sent a patch again which it has corrected a *coding style* and a new description in a kernel-parameters.txt file (a suggestions for better description are welcome).
I think that this can be a *last version* of a patch.
Because I am *newbie* in a kernel hacking I hope that someone will had been written me what now with it ? Maybe send this patch *directly* to *kernel guru* such as Andrew
Morton which manages a -mm series ?

diff -urp linux-2.6.24-orig/Documentation/kernel-parameters.txt linux-2.6.24/Documentation/kernel-parameters.txt

Documentation/kernel-parameters.txt +2 -0

@@ -381,6 +381,8 @@ and is between 256 and 4096 characters. 
 			Value can be changed at runtime via
 				/selinux/checkreqprot.
 
+	chroot=		[KNL] change a root for an init process.
+
 	clock=		[BUGS=X86-32, HW] gettimeofday clocksource override.
 			[Deprecated]
 			Forces specified clocksource (if available) to be used

diff -urp linux-2.6.24-orig/init/main.c linux-2.6.24/init/main.c

init/main.c +12 -0

@@ -755,8 +755,20 @@ static void __init do_pre_smp_initcalls(
 		spawn_softlockup_task();
 }
 
+static void *chroot_str;
+static int __init chroot_setup(char *str)
+{
+	chroot_str = str;
+	return 1;
+}
+__setup("chroot=", chroot_setup);
+
 static void run_init_process(char *init_filename)
 {
+	if (chroot_str)
+		if (sys_chroot(chroot_str) < 0)
+			printk(KERN_WARNING "chroot=%s failed\n", chroot_str);
+
 	argv_init[0] = init_filename;
 	kernel_execve(init_filename, argv_init, envp_init);
 }

At last my patch is as simple as possible and it has *only* a *few lines of the code* and it can be used as *independent* method to various *hundred* distroes.

static void run_init_process(char *init_filename) {
+ if (chroot_str)
+ if (sys_chroot(chroot_str) < 0)
+ printk(KERN_WARNING "chroot=%s failed\n", chroot_str);
+

I think that procces which has pid 0 is a special procces because it

removes a *zombie* procceses so it is good to use a *dedicated* program for it such as a /sbin/init . /usr/sbin/chroot doesn't remove a *zombie* procceses :-(

Quoted 2 lines

In the short this patch has added a new chroot= kernel parameter which can be used to changing a chroot of an init process before it will has been runed.

Wouldn't booting with 'init=/usr/sbin/chroot /path /sbin/init' achieve the same effect?
Haven't tested it, just wondering.