2007-11-06 10:40:51

by Al Boldi

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

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 <[email protected]>
Cc: Andrew Morton <[email protected]>
Signed-off-by: Al Boldi <[email protected]>

---

--- 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();
}

2007-11-06 20:10:33

by Al Boldi

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

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 <[email protected]>
> Cc: Andrew Morton <[email protected]>
> Signed-off-by: Al Boldi <[email protected]>
>
> ---
>
> --- 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

2007-11-06 20:13:30

by H. Peter Anvin

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

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

2007-11-06 21:14:25

by Al Boldi

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

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

2007-11-06 21:25:34

by H. Peter Anvin

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

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

2007-11-09 04:37:10

by Andrew Morton

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

> On Tue, 6 Nov 2007 13:40:26 +0300 Al Boldi <[email protected]> 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 <[email protected]>
> Cc: Andrew Morton <[email protected]>
> Signed-off-by: Al Boldi <[email protected]>
>
> ---
>
> --- 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.

2007-11-09 04:57:46

by Al Boldi

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

Andrew Morton wrote:
> > On Tue, 6 Nov 2007 13:40:26 +0300 Al Boldi <[email protected]> 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 <[email protected]>
> > Cc: Andrew Morton <[email protected]>
> > Signed-off-by: Al Boldi <[email protected]>
> >
> > ---
> >
> > --- 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