[PATCH] init: Introduce rootdir bootparm to select which dir to sys_chroot

[PATCH] init: Introduce rootdir bootparm to select which dir to sys_chroot

[Al Boldi]

This patch introduces a rootdir kernel boot parameter, which specifies the 
path to the kernel sys_chroot boot dir.

This is useful for systems that have more than one distribution installed on 
the same fs/partition.


Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Boldi <a1426z@gawab.com>

---

--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -252,6 +252,15 @@ __setup("rootflags=", root_data_setup);
 __setup("rootfstype=", fs_names_setup);
 __setup("rootdelay=", root_delay_setup);
 
+static char * __initdata root_dir;
+static int __init root_dir_setup(char *str)
+{
+	root_dir = strcat("./",str);
+	return 1;
+}
+
+__setup("rootdir=", root_dir_setup);
+
 static void __init get_fs_names(char *page)
 {
 	char *s = page;
@@ -469,6 +478,10 @@ void __init prepare_namespace(void)
 	mount_root();
 out:
 	sys_mount(".", "/", NULL, MS_MOVE, NULL);
+
+	if(root_dir)
+		sys_chdir(root_dir);
+
 	sys_chroot(".");
 	security_sb_post_mountroot();
 }

Re: [PATCH] init: Introduce rootdir bootparm to select which dir to sys_chroot

[H. Peter Anvin]

Al Boldi wrote:
> Al Boldi wrote:
>> This patch introduces a rootdir kernel boot parameter, which specifies the
>> path to the kernel sys_chroot boot dir.
>>
>> This is useful for systems that have more than one distribution installed
>> on the same fs/partition.

This seems like something that should be done via an initramfs.

	-hpa

Re: [PATCH] init: Introduce rootdir bootparm to select which dir to sys_chroot

[H. Peter Anvin]

Al Boldi wrote:
> H. Peter Anvin wrote:
>> Al Boldi wrote:
>>> Al Boldi wrote:
>>>> This patch introduces a rootdir kernel boot parameter, which specifies
>>>> the path to the kernel sys_chroot boot dir.
>>>>
>>>> This is useful for systems that have more than one distribution
>>>> installed on the same fs/partition.
>> This seems like something that should be done via an initramfs.
> 
> Agreed. But, not everybody boots their systems via initramfs, and even if 
> they did, they also have to know how to reconfigure it.
> 
> In contrast, this patch offers the rootdir functionality as a simple bootparm 
> and without any extra initramfs dependency.
> 

And yet another hack in the kernel!

Instead of heaping hack du jour into the kernel, write a small initramfs 
that provides the appropriate functionality, please.

	-hpa

Re: [PATCH] init: Introduce rootdir bootparm to select which dir to sys_chroot

[Al Boldi]

Al Boldi wrote:
> This patch introduces a rootdir kernel boot parameter, which specifies the
> path to the kernel sys_chroot boot dir.
>
> This is useful for systems that have more than one distribution installed
> on the same fs/partition.
>
>
> Cc: H. Peter Anvin <hpa@zytor.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Al Boldi <a1426z@gawab.com>
>
> ---
>
> --- a/init/do_mounts.c
> +++ b/init/do_mounts.c
> @@ -252,6 +252,15 @@ __setup("rootflags=", root_data_setup);
>  __setup("rootfstype=", fs_names_setup);
>  __setup("rootdelay=", root_delay_setup);
>
> +static char * __initdata root_dir;
> +static int __init root_dir_setup(char *str)
> +{
> +	root_dir = strcat("./",str);

This line is probably using an overloaded function that does not exist.
Use this instead:

static char __initdata root_dir[128];
static int __init root_dir_setup(char *str)
{
	strcpy(root_dir, "./");
	strlcat(root_dir, str, sizeof(root_dir) - strlen(root_dir) - 1);
	return 1;
}

> +__setup("rootdir=", root_dir_setup);
> +
>  static void __init get_fs_names(char *page)
>  {
>  	char *s = page;
> @@ -469,6 +478,10 @@ void __init prepare_namespace(void)
>  	mount_root();
>  out:
>  	sys_mount(".", "/", NULL, MS_MOVE, NULL);
> +
> +	if(root_dir)
> +		sys_chdir(root_dir);
> +
>  	sys_chroot(".");
>  	security_sb_post_mountroot();
>  }


Thanks!

--
Al

Re: [PATCH] init: Introduce rootdir bootparm to select which dir to sys_chroot

[Al Boldi]

H. Peter Anvin wrote:
> Al Boldi wrote:
> > Al Boldi wrote:
> >> This patch introduces a rootdir kernel boot parameter, which specifies
> >> the path to the kernel sys_chroot boot dir.
> >>
> >> This is useful for systems that have more than one distribution
> >> installed on the same fs/partition.
>
> This seems like something that should be done via an initramfs.

Agreed. But, not everybody boots their systems via initramfs, and even if 
they did, they also have to know how to reconfigure it.

In contrast, this patch offers the rootdir functionality as a simple bootparm 
and without any extra initramfs dependency.


Thanks!

--
Al

Re: [PATCH] init: Introduce rootdir bootparm to select which dir to sys_chroot

[Andrew Morton]

> On Tue, 6 Nov 2007 13:40:26 +0300 Al Boldi <a1426z@gawab.com> wrote:
> 
> This patch introduces a rootdir kernel boot parameter, which specifies the 
> path to the kernel sys_chroot boot dir.
> 
> This is useful for systems that have more than one distribution installed on 
> the same fs/partition.
> 
> 
> Cc: H. Peter Anvin <hpa@zytor.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Al Boldi <a1426z@gawab.com>
> 
> ---
> 
> --- a/init/do_mounts.c
> +++ b/init/do_mounts.c
> @@ -252,6 +252,15 @@ __setup("rootflags=", root_data_setup);
>  __setup("rootfstype=", fs_names_setup);
>  __setup("rootdelay=", root_delay_setup);
>  
> +static char * __initdata root_dir;
> +static int __init root_dir_setup(char *str)
> +{
> +	root_dir = strcat("./",str);
> +	return 1;
> +}
> +
> +__setup("rootdir=", root_dir_setup);

Please update Documentation/kernel-parameters.txt when adding __setup
options.

>  static void __init get_fs_names(char *page)
>  {
>  	char *s = page;
> @@ -469,6 +478,10 @@ void __init prepare_namespace(void)
>  	mount_root();
>  out:
>  	sys_mount(".", "/", NULL, MS_MOVE, NULL);
> +
> +	if(root_dir)
> +		sys_chdir(root_dir);
> +

Please run scripts/checkpatch.pl across all patches before sending them to
anyone.

Re: [PATCH] init: Introduce rootdir bootparm to select which dir to sys_chroot

[Al Boldi]

Andrew Morton wrote:
> > On Tue, 6 Nov 2007 13:40:26 +0300 Al Boldi <a1426z@gawab.com> wrote:
> >
> > This patch introduces a rootdir kernel boot parameter, which specifies
> > the path to the kernel sys_chroot boot dir.
> >
> > This is useful for systems that have more than one distribution
> > installed on the same fs/partition.
> >
> >
> > Cc: H. Peter Anvin <hpa@zytor.com>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Signed-off-by: Al Boldi <a1426z@gawab.com>
> >
> > ---
> >
> > --- a/init/do_mounts.c
> > +++ b/init/do_mounts.c
> > @@ -252,6 +252,15 @@ __setup("rootflags=", root_data_setup);
> >  __setup("rootfstype=", fs_names_setup);
> >  __setup("rootdelay=", root_delay_setup);
> >
> > +static char * __initdata root_dir;
> > +static int __init root_dir_setup(char *str)
> > +{
> > +	root_dir = strcat("./",str);
> > +	return 1;
> > +}
> > +
> > +__setup("rootdir=", root_dir_setup);
>
> Please update Documentation/kernel-parameters.txt when adding __setup
> options.

Sure.

If you think this feature is useful, which I think it is, then I probably 
need to resend with a doc update.  But bare in mind, this patch needs 
something like small hack to allow remounting root, which currently isn't 
possible.  I'm sure hpa is probably the genius to help out here.

>
> >  static void __init get_fs_names(char *page)
> >  {
> >  	char *s = page;
> > @@ -469,6 +478,10 @@ void __init prepare_namespace(void)
> >  	mount_root();
> >  out:
> >  	sys_mount(".", "/", NULL, MS_MOVE, NULL);
> > +
> > +	if(root_dir)
> > +		sys_chdir(root_dir);
> > +
>
> Please run scripts/checkpatch.pl across all patches before sending them to
> anyone.

Ok.


Thanks!

--
Al