Re: CLONE_PTRACE

[Mark Kettenis <kettenis _at_ wins.uva.nl>]

   Date: Sat, 19 Aug 2000 19:40:18 +0200
   From: "Andi Kleen" <ak _at_ suse.de>

   On Sat, Aug 19, 2000 at 03:37:04PM +0200, Mark Kettenis wrote:
   >    I once did a simple hack to solve that problem by adding a "VM
   >    identifier" to the /proc file system. The identifiers were
   >    just the in kernel addresses  of the mm_struct. You do a
   >    SIGSTOP and then just search /proc for other processes with
   >    the same VM.
   > 
   > And it would only work if the cloned processes are still sharing the
   > same process group, which ain't necessarily so.

   There are no restrictions regarding the process group.

I thought you sent the initial SIGSTOP to the process group, and
expected it to stop all possible interesting processes before
searching /proc.  Seems that's not what you were doing.

   > True, but it is certainly a common case that GDB is attached right
   > from the start.  And even the vmid approach would benefit from
   > notifications of new threads created after the initial
   > attach.  I don't think, constantly monitoring /proc for new threads is
   > a viable alternative.

   The alternative is to run a system call ptrace and look for clone and 
   fork (and optimizing that by adding a syscall trace wakeup filter to the
   kernel). It actually works fine, I did that in the past.

The filter is probably pretty essential to get adequate performance.
I still think that my proposed change is cleaner.

Mark


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