Re: [BProc] clone support

[<er...@he...>]

On Wed, Jul 30, 2003 at 10:55:12PM -0400, Nicholas Henke wrote:
> On Tue, 2003-07-01 at 11:05, er...@he... wrote:
> > 
> > I believe clone works.  Most of the interesting stuff with clone is
> > local to the node and BProc doesn't get involved at all.  So, in
> > theory, it should be possible to make Java work.
> 
> Ok -- finally getting around to tracking this down again. 
> 
> > In terms of what needs to be done, that depends entirely on what
> > you're trying to run.  I've done some simple pthreads things on nodes
> > w/o problems.  The first place to look is probably strace output of a
> > program that fails.  Then try and figure out how what the app is
> > seeing differs from what it's expecting.
> 
> Ok -- attached is the end of the strace from 'strace -f bpsh 7
> /usr/java/j2sdk1.4.1_01/bin/java -version'. There are some calls to
> SYS_223, which I am guessing is the bproc syscall. I am going to attempt
> to decipher those calls a bit, but I would appreciate any help you may
> have on this one.

I think you're going to have some difficulty getting good/clean
straces if you're doing strace -f with bpsh.  The -f flag doesn't
catch the children of bpsh since strace doesn't recognize
bproc_vexecmove_io as a variant of fork() (which it is).

The "-f" flag is racy in general.  The child process will likely run a
bit before strace gets a chance to attach to it.  This is presuming
that strace isn't quite clever enough to force CLONE_PTRACE yet.  I'm
not sure if it is.  It might be.  strace might be problematic for Java
in general since it might call clone a lot on its own.

Anyway, the point of this rambling story is that when I need to strace
something on a slave node, I usually end up copying the binary out to
the slave node and doing something like:

bpsh X strace blah

That way bpsh doesn't get caught in the strace.

Oh, an SYS_223 is BProc.  I wouldn't bother trying to figure out what
those calls are since it's bpsh doing them and not Java.  It's going
to be some node info stuff and then a call to bproc_vexecmove_io.

- Erik