[uml-devel] questions about mconsole driver and process address space

[uml-devel] questions about mconsole driver and process address space

[Weiming Liu]

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Hi. I am doing some experiment on mconsole driver. My wish is to create a
new user process from mconsole driver, modifying its address space, changing
its file mapping... Eventually may be I can migrate a process from host or
between UML instances. I am a newbie to both kernel and UML, and I have
several questions on implementation:

1. create a new process from a kernel thread. It seems that mconsole uses a
work queque, and requests are processed at kevents thread. Right now what I
am doing is, creating a new kernel thread and letting it call sys_ececve().
I then find its task_struct by looking for its name and its parent. It seems
stupid and maybe not correct. Is there any better way to do this?

2. I need to manipulate the process' address space (memory segments, file
mappings) like what flush_old_exec() and do_mmap() are doing. I cannot find
a way to call those functions since I am in a kernel thread, and it seems
too complicated by working directly on page tables and memory. How can this
be done in a convenient way?

Thanks,
Weiming Liu

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Re: [uml-devel] questions about mconsole driver and process address space

[Jeff Dike]

On Thu, Feb 28, 2008 at 06:28:53PM -0500, Weiming Liu wrote:
> Hi. I am doing some experiment on mconsole driver. My wish is to create a
> new user process from mconsole driver, modifying its address space, changing
> its file mapping... Eventually may be I can migrate a process from host or
> between UML instances. I am a newbie to both kernel and UML, and I have
> several questions on implementation:
> 
> 1. create a new process from a kernel thread. It seems that mconsole uses a
> work queque, and requests are processed at kevents thread. Right now what I
> am doing is, creating a new kernel thread and letting it call sys_ececve().
> I then find its task_struct by looking for its name and its parent. It seems
> stupid and maybe not correct. Is there any better way to do this?

Use a completion:

In the parent, do
   DECLARE_COMPLETION(c)
   kernel_thread()
   wait_for_completion(&c)
   child_task = my_task;

In the child, do
   my_task = current;
   complete(&c);

You'll also want to wrap a semaphore around the whole thing.

> 2. I need to manipulate the process' address space (memory segments, file
> mappings) like what flush_old_exec() and do_mmap() are doing. I cannot find
> a way to call those functions since I am in a kernel thread, and it seems
> too complicated by working directly on page tables and memory. How can this
> be done in a convenient way?

There are helpers for all these things.

      	  	      Jeff

-- 
Work email - jdike at linux dot intel dot com

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