From a9377073ff39cd47d61fe06ee6470f9c6b354e5b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Thomas=20G=C3=B6ttgens?= <tgoettgens@gmail.com>
Date: Mon, 5 Oct 2026 10:12:43 +0200
Subject: [PATCH] Count InternalFS cache pages dropped after repeated flush
 failures

A cached page whose flush fails three times in a row is dropped, and
with it writes LittleFS was already told had succeeded. Count each drop
in flash_nrf5x_stats.pages_dropped, so the loss shows in the flash
flight recorder.
---
 libraries/InternalFileSytem/src/flash/flash_cache.c | 2 ++
 libraries/InternalFileSytem/src/flash/flash_cache.h | 1 +
 libraries/InternalFileSytem/src/flash/flash_nrf5x.c | 3 ++-
 libraries/InternalFileSytem/src/flash/flash_nrf5x.h | 1 +
 4 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/libraries/InternalFileSytem/src/flash/flash_cache.c b/libraries/InternalFileSytem/src/flash/flash_cache.c
index dbe288d..16c7496 100644
--- a/libraries/InternalFileSytem/src/flash/flash_cache.c
+++ b/libraries/InternalFileSytem/src/flash/flash_cache.c
@@ -118,6 +118,8 @@ bool flash_cache_flush (flash_cache_t* fc)
   // included, and its data does not survive a reboot anyway.
   if ( ok || ++fc->flush_failures >= FLASH_CACHE_MAX_FLUSH_FAILURES )
   {
+    // Writes already reported as done are lost with it
+    if ( !ok && fc->pages_dropped ) (*fc->pages_dropped)++;
     fc->cache_addr = FLASH_CACHE_INVALID_ADDR;
     fc->flush_failures = 0;
   }
diff --git a/libraries/InternalFileSytem/src/flash/flash_cache.h b/libraries/InternalFileSytem/src/flash/flash_cache.h
index fa6a0ca..3414c07 100644
--- a/libraries/InternalFileSytem/src/flash/flash_cache.h
+++ b/libraries/InternalFileSytem/src/flash/flash_cache.h
@@ -44,6 +44,7 @@ typedef struct
     uint32_t cache_addr;
     uint8_t* cache_buf;
     uint8_t  flush_failures; // consecutive failed flushes of the cached page
+    uint32_t* pages_dropped; // counts pages given up after FLASH_CACHE_MAX_FLUSH_FAILURES, may be NULL
 } flash_cache_t;
 
 #ifdef __cplusplus
diff --git a/libraries/InternalFileSytem/src/flash/flash_nrf5x.c b/libraries/InternalFileSytem/src/flash/flash_nrf5x.c
index 30c5d46..f1ee2c8 100644
--- a/libraries/InternalFileSytem/src/flash/flash_nrf5x.c
+++ b/libraries/InternalFileSytem/src/flash/flash_nrf5x.c
@@ -330,7 +330,8 @@ static flash_cache_t _cache =
   .verify     = fal_verify,
 
   .cache_addr = FLASH_CACHE_INVALID_ADDR,
-  .cache_buf  = _cache_buffer
+  .cache_buf  = _cache_buffer,
+  .pages_dropped = &flash_nrf5x_stats.pages_dropped
 };
 
 //--------------------------------------------------------------------+
diff --git a/libraries/InternalFileSytem/src/flash/flash_nrf5x.h b/libraries/InternalFileSytem/src/flash/flash_nrf5x.h
index 0c0fc1d..fdae711 100644
--- a/libraries/InternalFileSytem/src/flash/flash_nrf5x.h
+++ b/libraries/InternalFileSytem/src/flash/flash_nrf5x.h
@@ -55,6 +55,7 @@ typedef struct
   uint32_t max_ticks;    // longest completed operation
   uint32_t last_result;  // NRF_SUCCESS or the last error code
   uint32_t written_off;  // completions given up as lost once the SoftDevice accepted a later operation
+  uint32_t pages_dropped; // cached pages given up after repeated flush failures, losing their writes
 } flash_nrf5x_stats_t;
 
 extern flash_nrf5x_stats_t flash_nrf5x_stats;