4 * Core of algorithm for writing output to devices which don't like
5 * constant stopping and starting, such as tape drives. This is:
6 * Copyright (C) 1997-1998,2000-2001 Ian Jackson <ian@chiark.greenend.org.uk>
8 * writebuffer is part of chiark backup, a system for backing up GNU/Linux
9 * and other UN*X-compatible machines, as used on chiark.greenend.org.uk.
11 * Copyright (C) 1997-1998,2000-2001 Ian Jackson <ian@chiark.greenend.org.uk>
12 * Copyright (C) 1999 Peter Maydell <pmaydell@chiark.greenend.org.uk>
14 * This is free software; you can redistribute it and/or modify
15 * it under the terms of the GNU General Public License as
16 * published by the Free Software Foundation; either version 2,
17 * or (at your option) any later version.
19 * This is distributed in the hope that it will be useful, but
20 * WITHOUT ANY WARRANTY; without even the implied warranty of
21 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
22 * GNU General Public License for more details.
24 * You should have received a copy of the GNU General Public
25 * License along with this file; if not, write to the Free Software
26 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
30 static size_t waitfill;
33 void wrbufcore_startup(void) {
34 waitfill= (buffersize*3)/4;
38 void wrbufcore_mainloop(void) {
41 while (!seeneof || used) {
43 FD_ZERO(&readfds); if (!seeneof && used+1<buffersize) FD_SET(0,&readfds);
44 FD_ZERO(&writefds); if (writing) FD_SET(1,&writefds);
48 if (FD_ISSET(1,&writefds) && !FD_ISSET(0,&readfds) && !used) {
53 if (FD_ISSET(0,&readfds)) {
54 r= read(0,rp,min(buffersize-1-used,buf+buffersize-rp));
58 if (!(errno == EAGAIN || errno == EINTR)) { perror("read"); exit(1); }
62 if (rp == buf+buffersize) rp=buf;
64 if (used > waitfill) writing=1;
67 if (FD_ISSET(1,&writefds) && used) {
68 r= write(1,wp,min(used,buf+buffersize-wp));
70 if (!(errno == EAGAIN || errno == EINTR)) { perror("write"); exit(1); }
74 if (wp == buf+buffersize) wp=buf;