Count InternalFS cache pages dropped after repeated flush failures

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;
   }

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

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
 };
 
 //--------------------------------------------------------------------+

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;