usr/src/cmd/lp/lib/msgs/write_fifo.c

   1 /*
   2  * CDDL HEADER START
   3  *
   4  * The contents of this file are subject to the terms of the
   5  * Common Development and Distribution License, Version 1.0 only
   6  * (the "License").  You may not use this file except in compliance
   7  * with the License.
   8  *
   9  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
  10  * or http://www.opensolaris.org/os/licensing.
  11  * See the License for the specific language governing permissions
  12  * and limitations under the License.
  13  *
  14  * When distributing Covered Code, include this CDDL HEADER in each
  15  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
  16  * If applicable, add the following below this CDDL HEADER, with the
  17  * fields enclosed by brackets "[]" replaced with your own identifying
  18  * information: Portions Copyright [yyyy] [name of copyright owner]
  19  *
  20  * CDDL HEADER END
  21  */
  22 /*      Copyright (c) 1984, 1986, 1987, 1988, 1989 AT&T */
  23 /*        All Rights Reserved   */
  24
  25
  26 #ident  "%Z%%M% %I%     %E% SMI"        /* SVr4.0 1.10  */
  27 /* LINTLIBRARY */
  28
  29 # include       <unistd.h>
  30 # include       <errno.h>
  31 # include       <string.h>
  32
  33 # include       "lp.h"
  34 # include       "msgs.h"
  35
  36 /*
  37 ** Choose at least one byte that won't appear in the body or header
  38 ** of a message.
  39 */
  40 unsigned char   Resync[HEAD_RESYNC_LEN]         = { 0x01, 0xFE };
  41 unsigned char   Endsync[HEAD_RESYNC_LEN]        = { 0x02, 0xFD };
  42
  43
  44 /*
  45 ** write_fifo() - WRITE A BUFFER WITH HEADER AND CHECKSUM
  46 */
  47
  48 #if     defined(__STDC__)
  49 int write_fifo ( int fifo, char * buf, unsigned int size )
  50 #else
  51 int write_fifo (fifo, buf, size)
  52     int                 fifo;
  53     char                *buf;
  54     unsigned int        size;
  55 #endif
  56 {
  57     unsigned short      chksum  = 0;
  58     int                 wbytes  = 0;
  59
  60     (void)memcpy (buf + HEAD_RESYNC, Resync, HEAD_RESYNC_LEN);
  61     (void)memcpy (buf + TAIL_ENDSYNC(size), Endsync, TAIL_ENDSYNC_LEN);
  62
  63     CALC_CHKSUM (buf, size, chksum);
  64     (void)htos (buf + TAIL_CHKSUM(size), chksum);
  65
  66
  67     /*
  68     ** A message must be written in one call, to avoid interleaving
  69     ** messages from several processes.
  70     **
  71     ** The caller is responsible for trapping SIGPIPE, so
  72     ** we just return what the "write()" system call does.
  73     **
  74     ** Well, almost.  If the pipe was almost full, we may have
  75     ** written a partial message.  If this is the case, we lie
  76     ** and say the pipe was full, so the caller can try again.
  77     **
  78     ** read_fifo can deal with a truncated message, so we let it
  79     ** do the grunt work associated with partial messages.
  80     **
  81     ** NOTE:  Writing the remainder of the message is not feasible
  82     ** as someone else may have written something to the fifo
  83     ** while we were setting up to retry.
  84     */
  85
  86     if ((wbytes = write(fifo, buf, size)) > 0)
  87         if (wbytes != size)
  88             return(0);
  89
  90     return(wbytes);
  91 }