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/common.h

@@ -154,6 +154,8 @@ typedef struct session {
 	void *backend_blur_context;
 	/// graphic drivers used
 	enum driver drivers;
+	/// file watch handle
+	void *file_watch_handle;
 	/// libev mainloop
 	struct ev_loop *loop;
 

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;
+}

src/file_watch.h

@@ -0,0 +1,10 @@
+#pragma once
+#include <stdbool.h>
+
+#include <ev.h>
+
+typedef void (*file_watch_cb_t)(void *);
+
+void *file_watch_init(EV_P);
+bool file_watch_add(void *, const char *, file_watch_cb_t, void *);
+void file_watch_destroy(EV_P_ void *);

src/meson.build

@@ -9,7 +9,7 @@ base_deps = [
 
 srcs = [ files('picom.c', 'win.c', 'c2.c', 'x.c', 'config.c', 'vsync.c', 'utils.c',
                'diagnostic.c', 'string_utils.c', 'render.c', 'kernel.c', 'log.c',
-               'options.c', 'event.c', 'cache.c', 'atom.c') ]
+               'options.c', 'event.c', 'cache.c', 'atom.c', 'file_watch.c') ]
 picom_inc = include_directories('.')
 
 cflags = []

src/picom.c

@@ -54,6 +54,7 @@
 #endif
 #include "atom.h"
 #include "event.h"
+#include "file_watch.h"
 #include "list.h"
 #include "options.h"
 #include "uthash_extra.h"
@@ -1538,6 +1539,11 @@ static void exit_enable(EV_P attr_unused, ev_signal *w, int revents attr_unused)
 	quit(ps);
 }
 
+static void config_file_change_cb(void *_ps) {
+	auto ps = (struct session *)_ps;
+	reset_enable(ps->loop, NULL, 0);
+}
+
 /**
  * Initialize a session.
  *
@@ -1935,6 +1941,12 @@ static session_t *session_init(int argc, char **argv, Display *dpy,
 		free(config_file_to_free);
 		exit(0);
 	}
+
+	ps->file_watch_handle = file_watch_init(ps->loop);
+	if (ps->file_watch_handle) {
+		file_watch_add(ps->file_watch_handle, config_file, config_file_change_cb, ps);
+	}
+
 	free(config_file_to_free);
 
 	if (bkend_use_glx(ps) && !ps->o.experimental_backends) {
@@ -2100,6 +2112,9 @@ static void session_destroy(session_t *ps) {
 		unredirect(ps);
 	}
 
+	file_watch_destroy(ps->loop, ps->file_watch_handle);
+	ps->file_watch_handle = NULL;
+
 	// Stop listening to events on root window
 	xcb_change_window_attributes(ps->c, ps->root, XCB_CW_EVENT_MASK,
 	                             (const uint32_t[]){0});