[PATCH] init: Warn on non-existent rdinit

[PATCH] init: Warn on non-existent rdinit

[Richard Weinberger]

Such a warning would have saved me some time...
Hopefully this printk() saves someone else's time. :-)

Signed-off-by: Richard Weinberger <richard@nod.at>
---
 init/main.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/init/main.c b/init/main.c
index 217ed23..43733c4 100644
--- a/init/main.c
+++ b/init/main.c
@@ -834,6 +834,8 @@ static int __init kernel_init(void * unused)
 		ramdisk_execute_command = "/init";
 
 	if (sys_access((const char __user *) ramdisk_execute_command, 0) != 0) {
+		printk(KERN_WARNING "Warning: unable to access %s!\n",
+					ramdisk_execute_command);
 		ramdisk_execute_command = NULL;
 		prepare_namespace();
 	}
-- 
1.7.7.3

Re: [PATCH] init: Warn on non-existent rdinit

[Eric W. Biederman]

Richard Weinberger <richard@nod.at> writes:

> Such a warning would have saved me some time...
> Hopefully this printk() saves someone else's time. :-)

The warning is wrong if you are not using an initramfs or an initial
ramdisk.

I expect what you want is something like:

diff --git a/init/main.c b/init/main.c
index 217ed23..8d53d28 100644
--- a/init/main.c
+++ b/init/main.c
@@ -830,10 +830,11 @@ static int __init kernel_init(void * unused)
         * the work
         */
 
-       if (!ramdisk_execute_command)
+       if (!ramdisk_execute_command &&
+           (sys_access((const char __user *)"/init", 0) == 0))
                ramdisk_execute_command = "/init";
 
-       if (sys_access((const char __user *) ramdisk_execute_command, 0) != 0) {
+       if (!ramdisk_execute_command) {
                ramdisk_execute_command = NULL;
                prepare_namespace();
        }


That way we don't clear ramdisk_execute_command if it was set and
we complain if we attempt exec the ramdisk_execute_command.

Eric

Re: [PATCH] init: Warn on non-existent rdinit

[Richard Weinberger]

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Am 05.01.2012 21:53, schrieb Eric W. Biederman:
> Richard Weinberger <richard@nod.at> writes:
> 
>> Such a warning would have saved me some time...
>> Hopefully this printk() saves someone else's time. :-)
> 
> The warning is wrong if you are not using an initramfs or an initial
> ramdisk.

Gnah, you're so right.
I did not test it without a ramdisk.

> I expect what you want is something like:
> 
> diff --git a/init/main.c b/init/main.c
> index 217ed23..8d53d28 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -830,10 +830,11 @@ static int __init kernel_init(void * unused)
>          * the work
>          */
>  
> -       if (!ramdisk_execute_command)
> +       if (!ramdisk_execute_command &&
> +           (sys_access((const char __user *)"/init", 0) == 0))
>                 ramdisk_execute_command = "/init";
>  
> -       if (sys_access((const char __user *) ramdisk_execute_command, 0) != 0) {
> +       if (!ramdisk_execute_command) {
>                 ramdisk_execute_command = NULL;
>                 prepare_namespace();
>         }

Why ramdisk_execute_command = NULL; in the !ramdisk_execute_command case?

> 
> That way we don't clear ramdisk_execute_command if it was set and
> we complain if we attempt exec the ramdisk_execute_command.

If "/init" does not exist we still don't get a warning.

Thanks,
//richard



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Re: [PATCH] init: Warn on non-existent rdinit

[Eric W. Biederman]

Richard Weinberger <richard@nod.at> writes:

> Am 05.01.2012 21:53, schrieb Eric W. Biederman:
>> Richard Weinberger <richard@nod.at> writes:
>> 
>>> Such a warning would have saved me some time...
>>> Hopefully this printk() saves someone else's time. :-)
>> 
>> The warning is wrong if you are not using an initramfs or an initial
>> ramdisk.
>
> Gnah, you're so right.
> I did not test it without a ramdisk.
>
>> I expect what you want is something like:
>> 
>> diff --git a/init/main.c b/init/main.c
>> index 217ed23..8d53d28 100644
>> --- a/init/main.c
>> +++ b/init/main.c
>> @@ -830,10 +830,11 @@ static int __init kernel_init(void * unused)
>>          * the work
>>          */
>>  
>> -       if (!ramdisk_execute_command)
>> +       if (!ramdisk_execute_command &&
>> +           (sys_access((const char __user *)"/init", 0) == 0))
>>                 ramdisk_execute_command = "/init";
>>  
>> -       if (sys_access((const char __user *) ramdisk_execute_command, 0) != 0) {
>> +       if (!ramdisk_execute_command) {
>>                 ramdisk_execute_command = NULL;
>>                 prepare_namespace();
>>         }
>
> Why ramdisk_execute_command = NULL; in the !ramdisk_execute_command
> case?

Because in my untested patch I didn't get as far as deleting that line.

>> That way we don't clear ramdisk_execute_command if it was set and
>> we complain if we attempt exec the ramdisk_execute_command.
>
> If "/init" does not exist we still don't get a warning.

Perhaps it has a /linuxrc.  If you can find a way of figuring out we
always need the file we can print an error.  Otherwise it is a case of
the kernel auto-detecting what to do, and not printing a warning when it
has decided there is no /init to play with.

Eric

Re: [PATCH] init: Warn on non-existent rdinit

[Richard Weinberger]

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Am 05.01.2012 23:00, schrieb Eric W. Biederman:
> Perhaps it has a /linuxrc.  If you can find a way of figuring out we
> always need the file we can print an error.  Otherwise it is a case of
> the kernel auto-detecting what to do, and not printing a warning when it
> has decided there is no /init to play with.
> 

If i find a nice way, I'll post a patch.

In my case I had a kernel with a built-in initramfs which contained a /linuxrc, but no /init.
I had no clue why the kernel always tried to boot from root=.

Thanks,
//richard



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