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 intselwait, nselcoll;/* * Select system call. */struct select_args {u_intnd;fd_set*in, *ou, *ex;structtimeval *tv;};select(p, uap, retval)register struct proc *p;register struct select_args *uap;int *retval;{fd_set ibits[3], obits[3];struct timeval atv;int s, ncoll, error = 0, timo;u_int ni;bzero((caddr_t)ibits, sizeof(ibits));bzero((caddr_t)obits, sizeof(obits));if (uap->nd > FD_SETSIZE)return (EINVAL);if (uap->nd > p->p_fd->fd_nfiles)uap->nd = p->p_fd->fd_nfiles;/* forgiving; slightly wrong */ni = howmany(uap->nd, NFDBITS) * sizeof(fd_mask);#definegetbits(name, x) /if (uap->name && / (error = copyin((caddr_t)uap->name, (caddr_t)&ibits[x], ni))) /goto done;getbits(in, 0);getbits(ou, 1);getbits(ex, 2);#undefgetbitsif (uap->tv) {error = copyin((caddr_t)uap->tv, (caddr_t)&atv,sizeof (atv));if (error)goto done;if (itimerfix(&atv)) {error = EINVAL;goto done;}s = splclock();timevaladd(&atv, (struct timeval *)&time);timo = hzto(&atv);/* * Avoid inadvertently sleeping forever. */if (timo == 0)timo = 1;splx(s);} elsetimo = 0;retry:ncoll = nselcoll;p->p_flag |= P_SELECT;error = selscan(p, ibits, obits, uap->nd, retval);if (error || *retval)goto done;s = splhigh();/* this should be timercmp(&time, &atv, >=) */if (uap->tv && (time.tv_sec > atv.tv_sec || time.tv_sec == atv.tv_sec && time.tv_usec >= atv.tv_usec)) {splx(s);goto done;}if ((p->p_flag & P_SELECT) == 0 || nselcoll != ncoll) {splx(s);goto retry;}p->p_flag &= ~P_SELECT;error = tsleep((caddr_t)&selwait, PSOCK | PCATCH, "select", timo);splx(s);if (error == 0)goto retry;done:p->p_flag &= ~P_SELECT;/* select is not restarted after signals... */if (error == ERESTART)error = EINTR;if (error == EWOULDBLOCK)error = 0;#defineputbits(name, x) /if (uap->name && / (error2 = copyout((caddr_t)&obits[x], (caddr_t)uap->name, ni))) /error = error2;if (error == 0) {int error2;putbits(in, 0);putbits(ou, 1);putbits(ex, 2);#undef putbits}return (error);