core: watch for configuration file changes

Automatically reset picom and reload the configuration when a change in
the configuration file is detected.

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

src/file_watch.c

@@ -0,0 +1,97 @@
+#include <errno.h>
+#include <string.h>
+#include <sys/inotify.h>
+
+#include <ev.h>
+#include <uthash.h>
+
+#include "file_watch.h"
+#include "list.h"
+#include "log.h"
+#include "utils.h"
+
+struct watched_file {
+	int wd;
+	void *ud;
+	file_watch_cb_t cb;
+
+	UT_hash_handle hh;
+};
+
+struct file_watch_registry {
+	struct ev_io w;
+
+	struct watched_file *reg;
+};
+
+static void file_watch_ev_cb(EV_P_ struct ev_io *w, int revent attr_unused) {
+	auto fwr = (struct file_watch_registry *)w;
+	struct inotify_event inotify_event;
+
+	while (true) {
+		auto ret = read(w->fd, &inotify_event, sizeof(struct inotify_event));
+		if (ret < 0) {
+			if (errno != EAGAIN) {
+				log_error("Failed to read from inotify fd: %s",
+				          strerror(errno));
+			}
+			break;
+		}
+
+		struct watched_file *wf = NULL;
+		HASH_FIND_INT(fwr->reg, &inotify_event.wd, wf);
+		if (!wf) {
+			log_warn("Got notification for a file I didn't watch.");
+			continue;
+		}
+		wf->cb(wf->ud);
+	}
+}
+
+void *file_watch_init(EV_P) {
+	log_debug("Starting watching for file changes");
+	int fd = inotify_init1(IN_NONBLOCK | IN_CLOEXEC);
+	if (fd < 0) {
+		log_error("inotify_init1 failed: %s", strerror(errno));
+		return NULL;
+	}
+	auto fwr = ccalloc(1, struct file_watch_registry);
+	ev_io_init(&fwr->w, file_watch_ev_cb, fd, EV_READ);
+	ev_io_start(EV_A_ & fwr->w);
+
+	return fwr;
+}
+
+void file_watch_destroy(EV_P_ void *_fwr) {
+	log_debug("Stopping watching for file changes");
+	auto fwr = (struct file_watch_registry *)_fwr;
+	struct watched_file *i, *tmp;
+
+	HASH_ITER(hh, fwr->reg, i, tmp) {
+		HASH_DEL(fwr->reg, i);
+		free(i);
+	}
+
+	ev_io_stop(EV_A_ & fwr->w);
+	close(fwr->w.fd);
+	free(fwr);
+}
+
+bool file_watch_add(void *_fwr, const char *filename, file_watch_cb_t cb, void *ud) {
+	log_debug("Adding \"%s\" to watched files", filename);
+	auto fwr = (struct file_watch_registry *)_fwr;
+	int wd = inotify_add_watch(fwr->w.fd, filename,
+	                           IN_CLOSE_WRITE | IN_MOVE_SELF | IN_DELETE_SELF);
+	if (wd < 0) {
+		log_error("Failed to watch file \"%s\": %s", filename, strerror(errno));
+		return false;
+	}
+
+	auto w = ccalloc(1, struct watched_file);
+	w->wd = wd;
+	w->cb = cb;
+	w->ud = ud;
+
+	HASH_ADD_INT(fwr->reg, wd, w);
+	return true;
+}