/* ttyread.c - ttyread */

#include <conf.h>
#include <kernel.h>
#include <tty.h>

/*------------------------------------------------------------------------
 * ttyread - read characters from a tty
 *------------------------------------------------------------------------
 */
int ttyread(pdev, buf, len)
struct devsw	*pdev;
char		*buf;
int		len;
{
    STATWORD	ps;
    struct tty	*ptty = (struct tty *)pdev->dvioblk;
    int		count;

    if (ptty->tty_state != TTYS_ALLOC)
	return SYSERR;
    
    if ((ptty->tty_iflags & TIF_EOF) && ptty->tty_icount == 0) {
	ptty->tty_iflags &= ~TIF_EOF;
	return EOF;
    }
    
    if (ptty->tty_iflags & TIF_NOBLOCK)
	if (scount(ptty->tty_isema) <= 0)
	    return SYSERR;
    
    disable(ps);
    wait(ptty->tty_isema);
    count = 0;
    while (count < len && ptty->tty_icount) {
	*buf++ = ptty->tty_in[ptty->tty_istart];
	count++;
	ptty->tty_icount--;
	ptty->tty_istart++;
	if (ptty->tty_istart >= IBLEN)
	    ptty->tty_istart = 0;
    }
    
/* wakeup other readers here */
    restore(ps);
    gettime(&ptty->tty_ctime);
    return count;
}