Please make sure you only send the email to the list only once (that's
enough :) ).
Dave
On Sat, 2004-06-26 at 01:53, prasanna wakhare wrote:
> hi,
> intel processors runs in 4 privilage mode,kernel runs
> in highest privilage mode
> ,You are in user mode so the segmenation hardware
> loaded the data and code segment descriptor
> with user data and user code segment,and you are
> trying to access the
> kernel data structure from user space which is
> something you never reach,
> So for accessing the kernel data struture yr data
> segment must be set with
> kernel data segment,but then yr code segment is set to
> user code segment,
> so processor will again generate exceptions as your
> user space code trying to access kernel space code,
> so better way is to do it in kernel modules which is
> something like dynamically loaded
> extensions to kernel code,
> where you can directly access the member of
> task_struct structure,
> but genrally the work should get done by using the
> exported funtions
> by kernel u get them in /proc/ksyms,
> more information about kernel programming you will get
> on web,
> and ofcourse the bible for every kernel programmer
> "linux device drivers"
> by rubini is always there.
> Prasanna
>
>
> --- Alexander Nyberg <alexn@telia.com> wrote:
> > > Hi all,
> > > I'm trying to develop a C program that access to
> > > process descriptor information but I have had some
> > > problem with libraries.
> > > In particular, I've developed a program like this:
> > >
> > > #include <linux/sched.h>
> > >
> > > int main(void){
> > > pid_t pid;
> > > ....
> > > task_struct process = find_task_by_pid(pid);
> > > ...
> > > }
> > >
> > > but the compiler can't find get_task_by_pid
> > function,
> > > while this is a function declared in
> > > include/linux/sched.h.
> > > What's wrong?
> >
> > The problem is that the function get_task_by_pid()
> > lives in the kernel,
> > and you cannot call arbitrary functions in the
> > kernel (think of what
> > that would mean to security and isolation). The
> > functions you can access
> > from user space are system calls.
> >
> > > Are there other methods to access process
> > descriptor
> > > pointer?
> >
> > If you need more than what is already available from
> > the task_struct you
> > would preferably add another system call to your
> > linux (there are other
> > ways too).
> >
> > Maybe something like:
> > sys_get_task_struct(pid_t pid, struct task_struct
> > __user *to)
> > {
> > task_struct *task = find_task_by_pid(pid);
> > copy_to_user(to, task, sizeof(struct task_struct));
> > }
> >
> > Alex
> >
> >
> > --
> > Kernelnewbies: Help each other learn about the Linux
> > kernel.
> > Archive:
> > http://mail.nl.linux.org/kernelnewbies/
> > FAQ: http://kernelnewbies.org/faq/
> >
> >
>
>
>
>
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> --
> Kernelnewbies: Help each other learn about the Linux kernel.
> Archive: http://mail.nl.linux.org/kernelnewbies/
> FAQ: http://kernelnewbies.org/faq/
>
>
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