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 3,
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, consult the Free Software
26 * Foundation's website at www.fsf.org, or the GNU Project website at
33 static size_t waitfill;
37 void wrbufcore_startup(void) {
38 waitfill= (buffersize*3)/4;
43 void fdsetset(int fd, fd_set *set) {
45 if (fd >= maxselfd) maxselfd= fd+1;
48 void wrbufcore_prepselect(int rdfd, int wrfd) {
50 if (rdfd>=0 && !seeneof && used+1<buffersize) fdsetset(rdfd,&readfds);
53 if (writing) fdsetset(wrfd,&writefds);
56 void wrbufcore_afterselect(int rdfd, int wrfd) {
59 if (FD_ISSET(wrfd,&writefds) &&
60 !(rdfd>=0 && FD_ISSET(rdfd,&readfds)) &&
62 wrbuf_report("stopping");
64 FD_CLR(wrfd,&writefds);
67 if (rdfd>=0 && FD_ISSET(rdfd,&readfds)) {
68 r= read(rdfd,rp,min(buffersize-1-used,buf+buffersize-rp));
71 wrbuf_report("seeneof");
73 if (!(errno == EAGAIN || errno == EINTR)) { perror("read"); exit(1); }
77 if (rp == buf+buffersize) rp=buf;
79 if (used > waitfill) {
80 if (!writing) wrbuf_report("starting");
85 if (FD_ISSET(wrfd,&writefds) && used) {
86 r= write(wrfd,wp,min(used,buf+buffersize-wp));
88 if (!(errno == EAGAIN || errno == EINTR)) { perror("write"); exit(1); }
92 if (wp == buf+buffersize) wp=buf;