+/* write message to buffer */
+void circ_message(const char *msg){
+ int l=strlen(msg)+1; /* count the whole message w/ '\0' included */
+
+ sem_down(s_semid);
+
+ /*
+ * Circular Buffer Algorithm:
+ * --------------------------
+ *
+ * Start-off w/ empty buffer of specific size SHM_SIZ
+ * Start filling it up w/ messages. I use '\0' as separator to break up messages.
+ * This is also very handy since we can do printf on message.
+ *
+ * Once the buffer is full we need to get rid of the first message in buffer and
+ * insert the new message. (Note: if the message being added is >1 message then
+ * we will need to "remove" >1 old message from the buffer). The way this is done
+ * is the following:
+ * When we reach the end of the buffer we set a mark and start from the beginning.
+ * Now what about the beginning and end of the buffer? Well we have the "head"
+ * index/pointer which is the starting point for the messages and we have "tail"
+ * index/pointer which is the ending point for the messages. When we "display" the
+ * messages we start from the beginning and continue until we reach "tail". If we
+ * reach end of buffer, then we just start from the beginning (offset 0). "head" and
+ * "tail" are actually offsets from the beginning of the buffer.
+ *
+ * Note: This algorithm uses Linux IPC mechanism w/ shared memory and semaphores to provide
+ * a threasafe way of handling shared memory operations.
+ */
+ if ( (buf->tail + l) < buf->size ){
+ /* before we append the message we need to check the HEAD so that we won't
+ overwrite any of the message that we still need and adjust HEAD to point
+ to the next message! */
+ if ( buf->tail < buf->head){
+ if ( (buf->tail + l) >= buf->head ){
+ /* we need to move the HEAD to point to the next message
+ * Theoretically we have enough room to add the whole message to the
+ * buffer, because of the first outer IF statement, so we don't have
+ * to worry about overflows here!
+ */
+ int k= buf->tail + l - buf->head; /* we need to know how many bytes
+ we are overwriting to make
+ enough room */
+ char *c=memchr(buf->data+buf->head + k,'\0',buf->size - (buf->head + k));
+ if (c != NULL) {/* do a sanity check just in case! */
+ buf->head = c - buf->data + 1; /* we need to convert pointer to
+ offset + skip the '\0' since
+ we need to point to the beginning
+ of the next message */
+ /* Note: HEAD is only used to "retrieve" messages, it's not used
+ when writing messages into our buffer */
+ }else{ /* show an error message to know we messed up? */
+ printf("Weird! Can't find the terminator token??? \n");
+ buf->head=0;
+ }
+ }
+ } /* in other cases no overflows have been done yet, so we don't care! */
+
+ /* we should be ok to append the message now */
+ strncpy(buf->data + buf->tail,msg,l); /* append our message */
+ buf->tail+=l; /* count full message w/ '\0' terminating char */
+ }else{
+ /* we need to break up the message and "circle" it around */
+ char *c;
+ int k=buf->tail + l - buf->size; /* count # of bytes we don't fit */
+
+ /* We need to move HEAD! This is always the case since we are going
+ * to "circle" the message.
+ */
+ c=memchr(buf->data + k ,'\0', buf->size - k);
+
+ if (c != NULL) /* if we don't have '\0'??? weird!!! */{
+ /* move head pointer*/
+ buf->head=c-buf->data+1;
+
+ /* now write the first part of the message */
+ strncpy(buf->data + buf->tail, msg, l - k - 1);
+
+ /* ALWAYS terminate end of buffer w/ '\0' */
+ buf->data[buf->size-1]='\0';
+
+ /* now write out the rest of the string to the beginning of the buffer */
+ strcpy(buf->data, &msg[l-k-1]);
+
+ /* we need to place the TAIL at the end of the message */
+ buf->tail = k + 1;
+ }else{
+ printf("Weird! Can't find the terminator token from the beginning??? \n");
+ buf->head = buf->tail = 0; /* reset buffer, since it's probably corrupted */
+ }
+
+ }
+ sem_up(s_semid);
+}
+#endif
+/* Note: There is also a function called "message()" in init.c */
+/* Print a message to the log file. */
+static void message (char *fmt, ...) __attribute__ ((format (printf, 1, 2)));
+static void message (char *fmt, ...)