Add log_remove_target

Don't need to deinit+init struct log any more just to switch log target
:)

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

src/compton.c

@@ -2654,12 +2654,12 @@ session_init(session_t *ps_old, int argc, char **argv) {
   };
 
   log_init_tls();
-  struct log_target *log_target = stderr_logger_new();
-  if (!log_target) {
+  auto stderr_logger = stderr_logger_new();
+  if (!stderr_logger) {
     fprintf(stderr, "Cannot create any logger, giving up.\n");
     abort();
   }
-  log_add_target_tls(log_target);
+  log_add_target_tls(stderr_logger);
 
   // Allocate a session and copy default values into it
   session_t *ps = cmalloc(session_t);
@@ -2788,14 +2788,11 @@ session_init(session_t *ps_old, int argc, char **argv) {
   get_cfg(&ps->o, argc, argv, shadow_enabled, fading_enable, hasneg, winopt_mask);
 
   if (ps->o.logpath) {
-    log_target = file_logger_new(ps->o.logpath);
-    if (log_target) {
-      auto level = log_get_level_tls();
+    auto l = file_logger_new(ps->o.logpath);
+    if (l) {
       log_info("Switching to log file: %s", ps->o.logpath);
-      log_deinit_tls();
-      log_init_tls();
-      log_set_level_tls(level);
-      log_add_target_tls(log_target);
+      log_remove_target_tls(stderr_logger);
+      log_add_target_tls(l);
     } else {
       log_error("Failed to setup log file %s, I will keep using stderr", ps->o.logpath);
     }

src/log.c

@@ -103,7 +103,22 @@ void log_add_target(struct log *l, struct log_target *tgt) {
 	l->head = tgt;
 }
 
-/// Destroy a log struct
+/// Remove a previously added log target for a log struct. If the log target was never
+/// added, nothing happens.
+void log_remove_target(struct log *l, struct log_target *tgt) {
+	struct log_target *now = l->head, **prev = &l->head;
+	while (now) {
+		if (now == tgt) {
+			*prev = now->next;
+			tgt->ops->destroy(tgt);
+			break;
+		}
+		prev = &now->next;
+		now = now->next;
+	}
+}
+
+/// Destroy a log struct and every log target added to it
 void log_destroy(struct log *l) {
 	// free all tgt
 	struct log_target *head = l->head;

src/log.h

@@ -20,8 +20,7 @@ enum log_level {
 #define LOG(level, x, ...)                                                                     \
 	do {                                                                                   \
 		if (LOG_LEVEL_##level >= log_get_level_tls()) {                                \
-			log_printf(tls_logger, LOG_LEVEL_##level, __func__, x,           \
-			           ##__VA_ARGS__);                                       \
+			log_printf(tls_logger, LOG_LEVEL_##level, __func__, x, ##__VA_ARGS__); \
 		}                                                                              \
 	} while (0)
 #define log_trace(x, ...) LOG(TRACE, x, ##__VA_ARGS__)
@@ -38,11 +37,15 @@ attr_printf(4, 5) void log_printf(struct log *, int level, const char *func,
                                   const char *fmt, ...);
 
 attr_malloc struct log *log_new(void);
+/// Destroy a log struct and every log target added to it
 attr_nonnull_all void log_destroy(struct log *);
 attr_nonnull(1) void log_set_level(struct log *l, int level);
 attr_pure enum log_level log_get_level(const struct log *l);
 attr_nonnull_all void log_add_target(struct log *, struct log_target *);
 attr_const enum log_level string_to_log_level(const char *);
+/// Remove a previously added log target for a log struct, and destroy it. If the log
+/// target was never added, nothing happens.
+void log_remove_target(struct log *l, struct log_target *tgt);
 
 extern thread_local struct log *tls_logger;
 
@@ -60,6 +63,11 @@ static inline attr_nonnull_all void log_add_target_tls(struct log_target *tgt) {
 	log_add_target(tls_logger, tgt);
 }
 
+static inline attr_nonnull_all void log_remove_target_tls(struct log_target *tgt) {
+	assert(tls_logger);
+	log_remove_target(tls_logger, tgt);
+}
+
 static inline attr_pure enum log_level log_get_level_tls(void) {
 	assert(tls_logger);
 	return log_get_level(tls_logger);