Hello linux-experts,
I am intercepting system calls in Linux kernel
2.4.28.
Pseudo-code:
------------
saved_old_syscall =
sys_call_table[sycallno(read)];
sys_call_table[read] = my_sys_call;
my_sys_call(file descriptor)
-------------
Call saved_old_syscall(file descriptor).
Now at this point, I want to determine whether
the system call blocks waiting for the file descriptor
resource. How can I do that? Should I modify the
kernel code only for this?
Can I check its state after the call as
if (task_current_state == INTERRUPTIBLE
|| UNINTERRUPTIBLE) to do this?
Thanks,
selva
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On Thu, 2005-01-06 at 22:58 -0800, selvakumar nagendran wrote:
> Hello linux-experts,
>
> I am intercepting system calls in Linux kernel
> 2.4.28.
>
> Pseudo-code:
> ------------
> saved_old_syscall =
> sys_call_table[sycallno(read)];
> sys_call_table[read] = my_sys_call;
>
> my_sys_call(file descriptor)
> -------------
> Call saved_old_syscall(file descriptor).
>
> Now at this point, I want to determine whether
> the system call blocks waiting for the file descriptor
> resource. How can I do that? Should I modify the
> kernel code only for this?
>
> Can I check its state after the call as
> if (task_current_state == INTERRUPTIBLE
> || UNINTERRUPTIBLE) to do this?
No, you can't, because by the time the syscall returns to you, it's
blocked, scheduled, unblocked, and been rescheduled. It's too late. I
don't think you can do what you want, without modifying all the syscalls
directly.
Besides, most blocks are for data, not on something like a semaphore.
What you really want is priority-inheritance semaphores, not
modification of syscalls. I seem to remember someone working on such a
beast, and the RTOS versions of Linux presumably have something like
this, so you could check around.
Daniel