Open files with O_DIRECT dependent on a compile-time DIRECT_IO #define.

O_DIRECT causes problems on (at least) a wheezy VM, and there are mixed
reports about its performance impact.  This patch makes it a
compile-time choice which should remain until it's been benchmarked.

src/client.c

@@ -485,7 +485,7 @@ void* client_serve(void* client_uncast)
 	
 	error_set_handler((cleanup_handler*) client_cleanup, client);
 	
-	debug("client: mmap");
+	info("client: mmaping file");
 	FATAL_IF_NEGATIVE(
 		open_and_mmap(
 			client->serve->filename,

src/ioutil.c

@@ -83,13 +83,22 @@ int open_and_mmap(const char* filename, int* out_fd, off64_t *out_size, void **o
 {
 	off64_t size;
 	
+	/* O_DIRECT seems to be intermittently supported.  Leaving it as
+	 * a compile-time option for now. */
+#ifdef DIRECT_IO
 	*out_fd = open(filename, O_RDWR | O_DIRECT | O_SYNC );
+#else
+	*out_fd = open(filename, O_RDWR | O_SYNC );
+#endif
+
 	if (*out_fd < 1) {
+		warn("open(%s) failed: does it exist?", filename);
 		return *out_fd;
 	}
 	
 	size = lseek64(*out_fd, 0, SEEK_END);
 	if (size < 0) {
+		warn("lseek64() failed");
 		return size;
 	}
 	if (out_size) {
@@ -100,6 +109,7 @@ int open_and_mmap(const char* filename, int* out_fd, off64_t *out_size, void **o
 		*out_map = mmap64(NULL, size, PROT_READ|PROT_WRITE, MAP_SHARED, 
 		  *out_fd, 0);
 		if (((long) *out_map) == -1) {
+			warn("mmap64() failed");
 			return -1;
 		}
 	}

src/mirror.c

@@ -244,11 +244,13 @@ void mirror_give_control( struct mirror * mirror )
 	 * The entrust signifies that all the data has been sent, and
 	 * the client is currently paused but not disconnected.
 	 * The disconnect signifies that the client has been
-	 * safely disconnected.
-	 * TODO: Disconnect the client!
+	 * safely prevented from making any more writes.
+	 *
+	 * Since we lock io and close the server it in mirror_on_exit before
+	 * releasing, we don't actually need to take any action between the
+	 * two here.
 	 */
 	socket_nbd_entrust( mirror->client );
-	debug("TODO: The client *should* be disconnected here, but isn't yet");
 	socket_nbd_disconnect( mirror->client );
 }