ttyread.c

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/* ttyread.c - ttyread */

#include <xinu.h>

/*------------------------------------------------------------------------
 *  ttyread  -  Read character(s) from a tty device (interrupts disabled)
 *------------------------------------------------------------------------
 */
devcall ttyread(
      struct dentry *devptr,    /* Entry in device switch table */
      char  *buff,          /* Buffer of characters     */
      int32 count           /* Count of character to read   */
    )
{
    struct  ttycblk *typtr;     /* Pointer to tty control block */
    int32   avail;          /* Characters available in buff.*/
    int32   nread;          /* Number of characters read    */
    int32   firstch;        /* First input character on line*/
    char    ch;         /* Next input character     */

    if (count < 0) {
        return SYSERR;
    }
    typtr= &ttytab[devptr->dvminor];

    if (typtr->tyimode != TY_IMCOOKED) {

        /* For count of zero, return all available characters */

        if (count == 0) {
            avail = semcount(typtr->tyisem);
            if (avail == 0) {
                return 0;
            } else {
                count = avail;
            }
        }
        for (nread = 0; nread < count; nread++) {
            *buff++ = (char) ttygetc(devptr);
        }
        return nread;
    }

    /* Block until input arrives */

    firstch = ttygetc(devptr);

    /* Check for End-Of-File */

    if (firstch == EOF) {
        return EOF;
    }

    /* Read up to a line */

    ch = (char) firstch;
    *buff++ = ch;
    nread = 1;
    while ( (nread < count) && (ch != TY_NEWLINE) &&
            (ch != TY_RETURN) ) {
        ch = ttygetc(devptr);
        *buff++ = ch;
        nread++;
    }
    return nread;
}