Re: Init.c, making it chroot
- From: "M. Warner Losh" <imp@xxxxxxxxxx>
- Date: Fri, 29 Dec 2006 11:34:25 -0700 (MST)
In message: <200612291736.kBTHa9kj021368@xxxxxxxxxxxxxxxxx>
Oliver Fromme <olli@xxxxxxxxxxxxxxxxx> writes:
:
: M. Warner Losh wrote:
: > BTW, here's a patch to test. Since FreeBSD has kenv(2), the patch is
: > actually very small.
:
: OK, I tried it. The patch applied cleanly to RELENG_6.
: The following line triggered a warning and caused the
: compilation to be aborted:
:
: > + kenv(KENV_GET, "init_chroot", init_chroot, sizeof(init_chroot));
:
: I get:
:
: /usr/src/sbin/init/init.c: In function `main':
: /usr/src/sbin/init/init.c:245: warning: passing arg 2 of `kenv' discards qualifiers from pointer target type
looks like kenv on RELENG_6 hadn't been const poisoned :-(.
: It compiles without problems. For testing I prepared an
: ISO image and put everything into a subdirectory called
: /chroot, except for /boot. /boot/loader.conf contains
: these lines:
:
: init_path="/ochroot/sbin/init"
: init_chroot="/ochroot"
:
: When I boot the CD (with -v), it freezes after printing
: these lines:
:
: cd9660: RockRidge Extension
: Lookup of /dev for devfs, error: 2
: start_init: trying /ochroot/sbin/init
OK. There's code in init to mount devfs, but it is disabled by
default.
The error message is from devfs_fixup. Early in the kernel boot, just
before we mount root, the kernel executes devfs_first. This mounts
devfs as / and creates a /dev -> / symlink. This allows mounting and
the like to work. Later, after we've mounted /, we do what linux
would call 'pivot root' and remount this devfs on / as /dev. That's
devfs_fixup.
: It seems that the kernel looks for /dev before starting
: init, hence before the chroot. So I created /dev in the
: ISO image and tried again. Now the "devfs error 2" line
: doesn't appear anymore, but it still freezes after the
: "start_init" line.
I can understand that. init doesn't try to mount devfs on /dev unless
you pass it -d. The -d comes from the boot loader somehow, but I've
not threaded to see how it could be set. It appears, from first
blush, that RB_SINGLE gets 's' set, but there's no way to get 'd'
set. Maybe init_chroot should imply it.
: I suspect that init expects devfs to be mounted on /dev
: _inside_ the chroot (i.e. on /ochroot/dev in my case),
: but I'm not sure if that's really causing the freeze.
: Unfortunately I haven't been able to analyse the problem
: further. Do you have an idea or hint?
Once we chroot, we need to have a sane environment inside the chroot.
Since the patches I posted chroot so early, /dev doesn't exist inside
of it...
: PS: The init_chroot feature would also be useful for
: making a shared CD/DVD that contains a standard FreeBSD
: installation (with sysinstall and "fixit") and a bootable
: live FS such as FreeSBIE at the same time.
The desire for a feature similar to this has come up many times,
usually in one-on-one meetings. I'm sold on its need.
I've enclosed a patch. delphi@ also checked the return value of kenv
too, which is more documented an interface.
Warner
Index: init.c
===================================================================
RCS file: /cache/ncvs/src/sbin/init/init.c,v
retrieving revision 1.62
diff -u -r1.62 init.c
--- init.c 8 Jun 2006 14:04:36 -0000 1.62
+++ init.c 29 Dec 2006 18:32:22 -0000
@@ -55,6 +55,7 @@
#include <db.h>
#include <errno.h>
#include <fcntl.h>
+#include <kenv.h>
#include <libutil.h>
#include <paths.h>
#include <signal.h>
@@ -187,6 +188,8 @@
int
main(int argc, char *argv[])
{
+ char init_chroot[PATH_MAX];
+ char icname[] = "init_chroot";
int c;
struct sigaction sa;
sigset_t mask;
@@ -239,6 +242,13 @@
*/
openlog("init", LOG_CONS|LOG_ODELAY, LOG_AUTH);
+ if (kenv(KENV_GET, icname, init_chroot, sizeof(init_chroot)) > 0) {
+ if (chdir(init_chroot) != 0 || chroot(".") != 0)
+ warning("Can't chroot to %s: %m", init_chroot);
+ else
+ devfs++;
+ }
+
/*
* Create an initial session.
*/
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