4 * A program for writing output to devices which don't like constant
5 * stopping and starting, such as tape drives. writebuffer 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.
31 #include <sys/types.h>
37 #ifndef RWBUFFER_SIZE_MB
38 #define RWBUFFER_SIZE_MB 16
41 #define BUFFER (RWBUFFER_SIZE_MB*1024*1024)
42 #define WAITFILL ((BUFFER*3)/4)
44 static inline int min(int a, int b) { return a<=b ? a : b; }
46 static void nonblock(int fd) {
48 r= fcntl(fd,F_GETFL,0); if (r == -1) { perror("fcntl getfl"); exit(1); }
50 if (fcntl(fd,F_SETFL,r) == -1) { perror("fcntl setfl"); exit(1); }
53 int main(int argc, const char *const *argv) {
54 static unsigned char buf[BUFFER];
56 unsigned char *wp, *rp;
57 int used,r,writing,seeneof;
62 fputs("readbuffer: no arguments allowed\n", stderr);
66 used=0; wp=rp=buf; writing=0; seeneof=0;
67 nonblock(0); nonblock(1);
68 while (!seeneof || used) {
69 FD_ZERO(&readfds); if (!seeneof && used+1<BUFFER) FD_SET(0,&readfds);
70 FD_ZERO(&writefds); if (writing) FD_SET(1,&writefds);
71 /*fprintf(stderr,"used %6d writing %d seeneof %d wp %8lx rp %8lx read %d write %d\n",
72 used,writing,seeneof,(unsigned long)(wp-buf),(unsigned long)(rp-buf),
73 FD_ISSET(0,&readfds),FD_ISSET(1,&writefds));*/
74 r= select(2,&readfds,&writefds,0,0);
75 /*fprintf(stderr,"\t readable %d writeable %d\n",
76 FD_ISSET(0,&readfds),FD_ISSET(1,&writefds));*/
78 if (errno == EINTR) continue;
79 perror("select"); exit(1);
81 if (FD_ISSET(1,&writefds) && !FD_ISSET(0,&readfds) && !used) {
84 /*fprintf(stderr,"\t buffers empty - stopping\n");*/
86 if (FD_ISSET(0,&readfds)) {
87 r= read(0,rp,min(BUFFER-1-used,buf+BUFFER-rp));
89 /*fprintf(stderr,"\t eof detected\n");*/
92 if (!(errno == EAGAIN || errno == EINTR)) { perror("read"); exit(1); }
93 fprintf(stderr,"\t read transient error\n");
95 /*fprintf(stderr,"\t read %d\n",r);*/
98 if (rp == buf+BUFFER) rp=buf;
99 /*fprintf(stderr,"\t starting writes\n");*/
101 if (used > WAITFILL) writing=1;
103 if (FD_ISSET(1,&writefds) && used) {
104 r= write(1,wp,min(used,buf+BUFFER-wp));
106 if (!(errno == EAGAIN || errno == EINTR)) { perror("write"); exit(1); }
107 /*fprintf(stderr,"\t write transient error\n");*/
109 /*fprintf(stderr,"\t wrote %d\n",r);*/
112 if (wp == buf+BUFFER) wp=buf;