if we get EWOULDBLOCK on a write then reduce the amount of data we are

trying to write. This guarantees that the maximum amount of data that
can be written at any one time is written.

io.c

@@ -319,6 +319,7 @@ static void writefd_unbuffered(int fd,char *buf,int len)
 	int fd_count, count;
 	struct timeval tv;
 	int reading;
+	int blocked=0;
 
 	no_flush++;
 
@@ -350,7 +351,8 @@ static void writefd_unbuffered(int fd,char *buf,int len)
 		}
 
 		if (FD_ISSET(fd, &w_fds)) {
-			int ret = write(fd,buf+total,len-total);
+			int n = (len-total)>>blocked;
+			int ret = write(fd,buf+total,n?n:1);
 
 			if (ret == -1 && errno == EINTR) {
 				continue;
@@ -358,10 +360,7 @@ static void writefd_unbuffered(int fd,char *buf,int len)
 
 			if (ret == -1 && 
 			    (errno == EAGAIN || errno == EWOULDBLOCK)) {
-				/* this shouldn't happen, if it does then
-				   sleep for a short time to prevent us
-				   chewing too much CPU */
-				u_sleep(100);
+				blocked++;
 				continue;
 			}
 
@@ -370,6 +369,7 @@ static void writefd_unbuffered(int fd,char *buf,int len)
 				exit_cleanup(1);
 			}
 
+			blocked = 0;
 			total += ret;
 			stats.total_written += ret;