automatically update the database with Linux inotify

This patch implements a light-weight inotify library, and watches all
directories below the music directory.  It updates all directories
where files changed after a delay of 5 seconds.

src/inotify_source.c

@@ -0,0 +1,163 @@
+/*
+ * Copyright (C) 2003-2009 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program 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 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "inotify_source.h"
+#include "fifo_buffer.h"
+
+#include <sys/inotify.h>
+#include <unistd.h>
+#include <errno.h>
+#include <stdbool.h>
+
+#undef G_LOG_DOMAIN
+#define G_LOG_DOMAIN "inotify"
+
+struct mpd_inotify_source {
+	int fd;
+
+	GIOChannel *channel;
+
+	/**
+	 * The channel's source id in the GLib main loop.
+	 */
+	guint id;
+
+	struct fifo_buffer *buffer;
+
+	mpd_inotify_callback_t callback;
+	void *callback_ctx;
+};
+
+/**
+ * A GQuark for GError instances.
+ */
+static inline GQuark
+mpd_inotify_quark(void)
+{
+	return g_quark_from_static_string("inotify");
+}
+
+static gboolean
+mpd_inotify_in_event(G_GNUC_UNUSED GIOChannel *_source,
+		     G_GNUC_UNUSED GIOCondition condition,
+		     gpointer data)
+{
+	struct mpd_inotify_source *source = data;
+	void *dest;
+	size_t length;
+	ssize_t nbytes;
+	const struct inotify_event *event;
+
+	dest = fifo_buffer_write(source->buffer, &length);
+	if (dest == NULL)
+		g_error("buffer full");
+
+	nbytes = read(source->fd, dest, length);
+	if (nbytes < 0)
+		g_error("failed to read from inotify: %s", g_strerror(errno));
+	if (nbytes == 0)
+		g_error("end of file from inotify");
+
+	fifo_buffer_append(source->buffer, nbytes);
+
+	while (true) {
+		const char *name;
+
+		event = fifo_buffer_read(source->buffer, &length);
+		if (event == NULL || length < sizeof(*event) ||
+		    length < sizeof(*event) + event->len)
+			break;
+
+		if (event->len > 0 && event->name[event->len - 1] == 0)
+			name = event->name;
+		else
+			name = NULL;
+
+		source->callback(event->wd, event->mask, name,
+				 source->callback_ctx);
+		fifo_buffer_consume(source->buffer,
+				    sizeof(*event) + event->len);
+	}
+
+	return true;
+}
+
+struct mpd_inotify_source *
+mpd_inotify_source_new(mpd_inotify_callback_t callback, void *callback_ctx,
+		       GError **error_r)
+{
+	struct mpd_inotify_source *source =
+		g_new(struct mpd_inotify_source, 1);
+
+	source->fd = inotify_init();
+	if (source->fd < 0) {
+		g_set_error(error_r, mpd_inotify_quark(), errno,
+			    "inotify_init() has failed: %s",
+			    g_strerror(errno));
+		g_free(source);
+		return NULL;
+	}
+
+	source->buffer = fifo_buffer_new(4096);
+
+	source->channel = g_io_channel_unix_new(source->fd);
+	source->id = g_io_add_watch(source->channel, G_IO_IN,
+				    mpd_inotify_in_event, source);
+
+	source->callback = callback;
+	source->callback_ctx = callback_ctx;
+
+	return source;
+}
+
+void
+mpd_inotify_source_free(struct mpd_inotify_source *source)
+{
+	g_source_remove(source->id);
+	g_io_channel_unref(source->channel);
+	fifo_buffer_free(source->buffer);
+	close(source->fd);
+	g_free(source);
+}
+
+int
+mpd_inotify_source_add(struct mpd_inotify_source *source,
+		       const char *path_fs, unsigned mask,
+		       GError **error_r)
+{
+	int wd = inotify_add_watch(source->fd, path_fs, mask);
+	if (wd < 0)
+		g_set_error(error_r, mpd_inotify_quark(), errno,
+			    "inotify_add_watch() has failed: %s",
+			    g_strerror(errno));
+
+	return wd;
+}
+
+void
+mpd_inotify_source_rm(struct mpd_inotify_source *source, unsigned wd)
+{
+	int ret = inotify_rm_watch(source->fd, wd);
+	if (ret < 0 && errno != EINVAL)
+		g_warning("inotify_rm_watch() has failed: %s",
+			  g_strerror(errno));
+
+	/* EINVAL may happen here when the file has been deleted; the
+	   kernel seems to auto-unregister deleted files */
+}