[Devel] Re: Namespaces exhausted CLONE_XXX bits problem

[Cedric Le Goater]

Pavel Emelyanov wrote:
> Cedric Le Goater wrote:
>> Pavel Emelyanov wrote:
>>> Dave Hansen wrote:
>>>> On Mon, 2008-01-14 at 16:36 -0500, Oren Laadan wrote:
>>>>> I second the concern of running out of 64 bits of flags. In fact, the
>>>>> problem with the flags is likely to be valid outside our context, and
>>>>> general to the linux kernel soon. Should we not discuss it there
>>>>> too ? 
>>>> It would be pretty easy to make a new one expandable:
>>>>
>>>> 	sys_newclone(int len, unsigned long *flags_array)
>>>>
>>>> Then you could give it a virtually unlimited number of "unsigned long"s
>>>> pointed to by "flags_array".
>>>>
>>>> Plus, the old clone just becomes:
>>>>
>>>>         sys_oldclone(unsigned long flags)
>>>>         {
>>>>         	do_newclone(1, &flags);
>>>>         }
>>>>
>>>> We could validate the flags array address in sys_newclone(), then call
>>>> do_newclone().
>>> Hmm. I have an idea how to make this w/o a new system call. This might
>>> look wierd, but. Why not stopple the last bit with a CLONE_NEWCLONE and
>>> consider the parent_tidptr/child_tidptr in this case as the pointer to 
>>> an array of extra arguments/flargs?
>> It's a bit hacky but it looks like a good idea to me !
>>
>> Shall we use parent_tidptr or child_tidptr to pass a extended array of 
>> flags only ? if we could pass the pid of the task to be cloned, it would 
>> be useful for c/r.
> 
> Yup. I think we can declare a
> 
> struct new_clone_arg {
> 	unsigned int size;
> };
> 
> and consider the xx_tidptr to be a pointer on it. After this we
> may sen patches that add fields to this structure.
> 
> E.g. first
> 
>  struct new_clone_arg {
>  	unsigned int size;
> +	unsigned long new_flags;
>  };
> 
> to add flags for cloning new namespaces. Later
> 
>  struct new_clone_arg {
>  	unsigned int size;
>  	unsigned long new_flags;
> +	int desired_pid;
>  };
> 
> and each code that needs to access the extra argument would need
> to check for new_clone_arg->size to be not less than the offset
> of the field he need an access to. E.g. like this:
> 
> #define clone_arg_has(arg, member)	({			\
> 	struct new_clone_arg *__carg = arg;			\
> 	(__carg->size >= offsetof(struct new_clone_arg, member) + \
> 		sizeof(__carg->member)) })
> 
> ...
> 
> if (!clone_arg_has(arg, desired_pid))
> 	return -EINVAL;
> 
> This would keep the API always compatible.

Pavel, this is pretty neat. 

I think we need to work on a patch now and send it to andrew and lkml@
to have a larger audience.

I doesn't seem to be a really big patch and I wondering how I could help. 
We still have to prepare something for security_task_create()

Thanks !

C.
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