#include <u.h>#include <libc.h>#include <thread.h>#include "threadimpl.h" voidprocexec(Channel *pidc, char *prog, char *args[]){	int n;	Proc *p;	Thread *t; 	_threaddebug(DBGEXEC, "procexec %s", prog);	/* must be only thread in proc */	p = _threadgetproc();	t = p->thread;	if(p->threads.head != t || p->threads.head->nextt != nil){		werrstr("not only thread in proc");	Bad:		if(pidc)			sendul(pidc, ~0);		return;	} 	/*	 * We want procexec to behave like exec; if exec succeeds,	 * never return, and if it fails, return with errstr set.	 * Unfortunately, the exec happens in another proc since	 * we have to wait for the exec'ed process to finish.	 * To provide the semantics, we open a pipe with the 	 * write end close-on-exec and hand it to the proc that	 * is doing the exec.  If the exec succeeds, the pipe will	 * close so that our read below fails.  If the exec fails,	 * then the proc doing the exec sends the errstr down the	 * pipe to us.	 */	if(pipe(p->exec.fd) < 0)		goto Bad;	snprint(p->exitstr, ERRMAX, "/fd/%d", p->exec.fd[1]);	if((n = open(p->exitstr, OWRITE|OCEXEC)) < 0){		close(p->exec.fd[0]);		close(p->exec.fd[1]);		goto Bad;	}	close(p->exec.fd[1]);	p->exec.fd[1] = n; 	while(p->needexec || p->newproc)		_sched(); 	/* exec in parallel via the scheduler */	p->exec.prog = prog;	p->exec.args = args;	p->needexec = 1;	_sched(); 	close(p->exec.fd[1]);	if((n = read(p->exec.fd[0], p->exitstr, ERRMAX-1)) > 0){	/* exec failed */		p->exitstr[n] = '\0';		errstr(p->exitstr, ERRMAX);		close(p->exec.fd[0]);		goto Bad;	}	close(p->exec.fd[0]); 	if(t->ret == -1)		goto Bad;	if(pidc)		sendul(pidc, t->ret); 	/* wait for exec'ed program, then exit */	_schedexecwait();} voidprocexecl(Channel *pidc, char *f, ...){	procexec(pidc, f, &f+1);}