From 991f74a62adc37790c661e7b1d2c30185ef93559 Mon Sep 17 00:00:00 2001
From: chrysn <chrysn@fsfe.org>
Date: Wed, 15 Dec 2021 14:34:26 +0100
Subject: [PATCH] sys/ztimer: ztimer_remove return its success

Co-authored-by: Marian Buschsieweke <maribu@users.noreply.github.com>
---
 sys/include/ztimer.h |  8 +++++++-
 sys/ztimer/core.c    | 15 +++++++++++----
 2 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/sys/include/ztimer.h b/sys/include/ztimer.h
index c7900a3873..70a52ac1e3 100644
--- a/sys/include/ztimer.h
+++ b/sys/include/ztimer.h
@@ -408,8 +408,14 @@ unsigned ztimer_is_set(const ztimer_clock_t *clock, const ztimer_t *timer);
  *
  * @param[in]   clock       ztimer clock to operate on
  * @param[in]   timer       timer entry to remove
+ *
+ * @retval  true    The timer was removed (and thus its callback neither was nor
+ *                  will be called by ztimer).
+ * @retval  false   The timer fired previously or is not set on the @p clock
+ *                  at all.
+ *
  */
-void ztimer_remove(ztimer_clock_t *clock, ztimer_t *timer);
+bool ztimer_remove(ztimer_clock_t *clock, ztimer_t *timer);
 
 /**
  * @brief   Post a message after a delay
diff --git a/sys/ztimer/core.c b/sys/ztimer/core.c
index 01205f1cf2..fea54c61ad 100644
--- a/sys/ztimer/core.c
+++ b/sys/ztimer/core.c
@@ -37,7 +37,7 @@
 #include "debug.h"
 
 static void _add_entry_to_list(ztimer_clock_t *clock, ztimer_base_t *entry);
-static void _del_entry_from_list(ztimer_clock_t *clock, ztimer_base_t *entry);
+static bool _del_entry_from_list(ztimer_clock_t *clock, ztimer_base_t *entry);
 static void _ztimer_update(ztimer_clock_t *clock);
 static void _ztimer_print(const ztimer_clock_t *clock);
 static uint32_t _ztimer_update_head_offset(ztimer_clock_t *clock);
@@ -68,18 +68,20 @@ unsigned ztimer_is_set(const ztimer_clock_t *clock, const ztimer_t *timer)
     return res;
 }
 
-void ztimer_remove(ztimer_clock_t *clock, ztimer_t *timer)
+bool ztimer_remove(ztimer_clock_t *clock, ztimer_t *timer)
 {
+    bool was_removed = false;
     unsigned state = irq_disable();
 
     if (_is_set(clock, timer)) {
         _ztimer_update_head_offset(clock);
-        _del_entry_from_list(clock, &timer->base);
+        was_removed = _del_entry_from_list(clock, &timer->base);
 
         _ztimer_update(clock);
     }
 
     irq_restore(state);
+    return was_removed;
 }
 
 uint32_t ztimer_set(ztimer_clock_t *clock, ztimer_t *timer, uint32_t val)
@@ -232,8 +234,10 @@ static uint32_t _ztimer_update_head_offset(ztimer_clock_t *clock)
     return now;
 }
 
-static void _del_entry_from_list(ztimer_clock_t *clock, ztimer_base_t *entry)
+static bool _del_entry_from_list(ztimer_clock_t *clock, ztimer_base_t *entry)
 {
+    bool was_removed = false;
+
     DEBUG("_del_entry_from_list()\n");
     ztimer_base_t *list = &clock->list;
 
@@ -254,6 +258,7 @@ static void _del_entry_from_list(ztimer_clock_t *clock, ztimer_base_t *entry)
                 list_entry->offset += entry->offset;
             }
 
+            was_removed = true;
             /* reset the entry's next pointer so _is_set() considers it unset */
             entry->next = NULL;
             break;
@@ -268,6 +273,8 @@ static void _del_entry_from_list(ztimer_clock_t *clock, ztimer_base_t *entry)
         pm_unblock(clock->block_pm_mode);
     }
 #endif
+
+    return was_removed;
 }
 
 static ztimer_t *_now_next(ztimer_clock_t *clock)