move rwbuffer to new cprogs directory

[chiark-utils.git] / cprogs / wrbufcore.c

diff --git a/cprogs/wrbufcore.c b/cprogs/wrbufcore.c
new file mode 100644 (file)
index 0000000..260f6d2
--- /dev/null
+++ b/cprogs/wrbufcore.c
@@ -0,0 +1,78 @@
+/*
+ * wrbufcore.c
+ *
+ * Core of algorithm for writing output to devices which don't like
+ * constant stopping and starting, such as tape drives.  This is:
+ *  Copyright (C) 1997-1998,2000-2001 Ian Jackson <ian@chiark.greenend.org.uk>
+ *
+ * writebuffer is part of chiark backup, a system for backing up GNU/Linux
+ * and other UN*X-compatible machines, as used on chiark.greenend.org.uk.
+ * chiark backup is:
+ *  Copyright (C) 1997-1998,2000-2001 Ian Jackson <ian@chiark.greenend.org.uk>
+ *  Copyright (C) 1999 Peter Maydell <pmaydell@chiark.greenend.org.uk>
+ *
+ * This is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2,
+ * or (at your option) any later version.
+ *
+ * This is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public
+ * License along with this file; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ *
+ */
+
+static size_t waitfill;
+static int writing;
+
+void wrbufcore_startup(void) {
+  waitfill= (buffersize*3)/4;
+  writing=0;
+}
+
+void wrbufcore_mainloop(void) {
+  int r;
+
+  while (!seeneof || used) {
+    
+    FD_ZERO(&readfds); if (!seeneof && used+1<buffersize) FD_SET(0,&readfds);
+    FD_ZERO(&writefds); if (writing) FD_SET(1,&writefds);
+
+    callselect();
+    
+    if (FD_ISSET(1,&writefds) && !FD_ISSET(0,&readfds) && !used) {
+      writing= 0;
+      FD_CLR(1,&writefds);
+    }
+
+    if (FD_ISSET(0,&readfds)) {
+      r= read(0,rp,min(buffersize-1-used,buf+buffersize-rp));
+      if (!r) {
+        seeneof=1; writing=1;
+      } else if (r<0) {
+        if (!(errno == EAGAIN || errno == EINTR)) { perror("read"); exit(1); }
+      } else {
+        used+= r;
+        rp+= r;
+        if (rp == buf+buffersize) rp=buf;
+      }
+      if (used > waitfill) writing=1;
+    }
+
+    if (FD_ISSET(1,&writefds) && used) {
+      r= write(1,wp,min(used,buf+buffersize-wp));
+      if (r<=0) {
+        if (!(errno == EAGAIN || errno == EINTR)) { perror("write"); exit(1); }
+      } else {
+        used-= r;
+        wp+= r;
+        if (wp == buf+buffersize) wp=buf;
+      }
+    }
+  }
+}