Found on davenant in /usr/local/lib (in use on anarres).

[chiark-utils.git] / backup / writebuffer.c

diff --git a/backup/writebuffer.c b/backup/writebuffer.c
new file mode 100644 (file)
index 0000000..c4fa9e7
--- /dev/null
+++ b/backup/writebuffer.c
@@ -0,0 +1,81 @@
+/**/
+
+#include <sys/time.h>
+#include <sys/types.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <errno.h>
+#include <unistd.h>
+
+#define BUFFER 16*1024*1024
+#define WAITFILL ((BUFFER*3)/4)
+
+static inline int min(int a, int b) { return a<=b ? a : b; }
+
+static void nonblock(int fd) {
+  int r;
+  r= fcntl(fd,F_GETFL,0); if (r == -1) { perror("fcntl getfl"); exit(1); }
+  r |= O_NDELAY;
+  if (fcntl(fd,F_SETFL,r) == -1) { perror("fcntl setfl"); exit(1); }
+}
+
+int main(void) {
+  static unsigned char buf[BUFFER];
+  
+  unsigned char *wp, *rp;
+  int used,r,writing,seeneof;
+  fd_set readfds;
+  fd_set writefds;
+
+  used=0; wp=rp=buf; writing=0; seeneof=0;
+  nonblock(0); nonblock(1);
+  while (!seeneof || used) {
+    FD_ZERO(&readfds); if (!seeneof && used+1<BUFFER) FD_SET(0,&readfds);
+    FD_ZERO(&writefds); if (writing) FD_SET(1,&writefds);
+/*fprintf(stderr,"used %6d writing %d seeneof %d wp %8lx rp %8lx read %d write %d\n",
+        used,writing,seeneof,(unsigned long)(wp-buf),(unsigned long)(rp-buf),
+        FD_ISSET(0,&readfds),FD_ISSET(1,&writefds));*/
+    r= select(2,&readfds,&writefds,0,0);
+/*fprintf(stderr,"\t readable %d writeable %d\n",
+        FD_ISSET(0,&readfds),FD_ISSET(1,&writefds));*/
+    if (r == -1) {
+      if (errno == EINTR) continue;
+      perror("select"); exit(1);
+    }
+    if (FD_ISSET(1,&writefds) && !FD_ISSET(0,&readfds) && !used) {
+      writing= 0;
+      FD_CLR(1,&writefds);
+/*fprintf(stderr,"\t buffers empty - stopping\n");*/
+    }
+    if (FD_ISSET(0,&readfds)) {
+      r= read(0,rp,min(BUFFER-1-used,buf+BUFFER-rp));
+      if (!r) {
+/*fprintf(stderr,"\t eof detected\n");*/
+        seeneof=1; writing=1;
+      } else if (r<0) {
+        if (!(errno == EAGAIN || errno == EINTR)) { perror("read"); exit(1); }
+fprintf(stderr,"\t read transient error\n");
+      } else {
+/*fprintf(stderr,"\t read %d\n",r);*/
+        used+= r;
+        rp+= r;
+        if (rp == buf+BUFFER) rp=buf;
+/*fprintf(stderr,"\t starting writes\n");*/
+      }
+      if (used > WAITFILL) writing=1;
+    }
+    if (FD_ISSET(1,&writefds) && used) {
+      r= write(1,wp,min(used,buf+BUFFER-wp));
+      if (r<=0) {
+        if (!(errno == EAGAIN || errno == EINTR)) { perror("write"); exit(1); }
+/*fprintf(stderr,"\t write transient error\n");*/
+      } else {
+/*fprintf(stderr,"\t wrote %d\n",r);*/
+        used-= r;
+        wp+= r;
+        if (wp == buf+BUFFER) wp=buf;
+      }
+    }
+  }
+  exit(0);
+}