Re: [musl] toybox: Rough edges in pending

[Rob Landley <rob-VoJi6FS/r0vR7s880joybQ@public.gmane.org>]

On 03/19/2013 06:09:39 AM, Szabolcs Nagy wrote:
> * Szabolcs Nagy <nsz-4P1ElwuDYu6sTnJN9+BGXg@public.gmane.org> [2013-03-19 10:42:25 +0100]:
> > * Isaac Dunham <idunham-N9AOi2cAC9ZBDgjK7y7TUQ@public.gmane.org> [2013-03-18 23:50:43 -0700]:
> > > execve("./toybox-musl", ["./toybox-musl", "sh", "-c", "ls"], [/*  
> 22 vars */]) = 0
> > ...
> > > ioctl(0, SNDCTL_TMR_TIMEBASE or TCGETS, {B9600 opost isig icanon  
> echo ...}) = 0
> > > vfork(Config.in README    kconfig scripts     toybox_unstripped  
> toys.h
> > > LICENSE   configure lib     toybox      toynet.h          www
> > > Makefile  generated main.c  toybox-musl toys
> > > )                                 = 27832
> > > --- SIGCHLD (Child exited) @ 0 (0) ---
> > > wait4(27832, [{WIFEXITED(s) && WEXITSTATUS(s) == 0}], 0, NULL) =  
> 27832
> > > pause(^C <unfinished ...>
> >
> > exit tries to flush some stdio buffers but it is locked
> >
> > maybe an issue around the way vfork is used by the shell
> 
> 
> this is what toybox sh does:
> 
>     cmd->pid = vfork();
>     if (!cmd->pid) xexec(cmd->argv);
>     else waitpid(cmd->pid, &status, 0);
> 
> 
> it's an incorrect use of vfork

It is indeed. I was going to add some plumbing to xexec() to exec  
/proc/self/exe in the internal toy called from toysh case, but toysh is  
unfinished and I'm not sure it's the best approach and potentially  
implementing the nofork logic with longjmp() for error handling works  
into that, although I have to prototype bits of that to figure out  
whether it's worth the effort.

(It's complicated. In bash you can't ctrl-z to suspend "read" because  
it's a shell builtin and doesn't have a separate process context to  
suspend, even though it can block. I feel it _should_ be possible to  
suspend this but that involves potentially calling fork() from the  
ctrl-z handler and is the shell not letting you do something obvious  
better than complicating the implementation? There's _details_ to  
getting this all right, and I haven't reopened the toysh can of worms  
because I'd need more than a month to reach the next good stopping  
point. The first week of which is a close re-reading of the SUSv4 shell  
stuff and the bash man page and digging up my old test cases. I have  
lots of lower hanging fruit to clear first.)

Rob