feat: spool records to a file store with a CRC-16 at rest

CMakeLists.txt

@@ -39,7 +39,7 @@ set(LWIP_CONTRIB_FREERTOS_DIR "${LWIP_DIR}/contrib/ports/freertos")
 # link target — only the header-configured packs below do.
 # https://docs.cososo.co.uk/solid-syslog/getting-started/#path-a--cmake-consumer
 # Pinned to a commit until there is a release tag to pin to.
-set(SOLIDSYSLOG_PLATFORMS "LwipRaw;Atomics;FreeRtos" CACHE STRING "" FORCE)
+set(SOLIDSYSLOG_PLATFORMS "LwipRaw;Atomics;FreeRtos;FatFs" CACHE STRING "" FORCE)
 
 # Compile-time limits. Every tunable is #ifndef-guarded, so this file only needs
 # the ones this device wants changed.
@@ -171,7 +171,7 @@ target_include_directories(baseline PRIVATE
 # library, or context struct sizes diverge between consumer and library.
 target_compile_definitions(baseline PRIVATE MBEDTLS_USER_CONFIG_FILE=${MBEDTLS_USER_CONFIG_HEADER})
 
-target_link_libraries(baseline PRIVATE mbedtls mbedx509 mbedcrypto SolidSyslog SolidSyslog::LwipRaw SolidSyslog::FreeRtos)
+target_link_libraries(baseline PRIVATE mbedtls mbedx509 mbedcrypto SolidSyslog SolidSyslog::LwipRaw SolidSyslog::FreeRtos SolidSyslog::FatFs)
 
 target_link_options(baseline PRIVATE
     -mcpu=cortex-m3 -mthumb

README.md

@@ -10,15 +10,16 @@ It builds on a baseline that simulates the sort of device you might be adding th
 measures itself: see [docs/baseline.md](docs/baseline.md) for what the baseline is, how the
 figures are made, and how to run it.
 
-## This stage — Time quality
+## This stage — File store
 
-The record gains a `timeQuality` SD-ELEMENT and a `sysUpTime` PARAM on `meta`. This device's clock
-free-runs on the tick after one reading at boot, so it reports `isSynced="0"` and the collector
-knows how far to trust the timestamp.
+Records spool to a block store on the volume the device already mounts — four blocks, one file
+each — instead of being held only in memory. The service task drains the ring into the store and
+sends from there, so a failed send costs a retry rather than the record. The CRC-16 written with
+each record catches corruption at rest, not tampering.
 
 <!-- STAGE-COST:START (generated by scripts/gen-cost-table.py — do not edit by hand) -->
 
-**Cost above baseline: Flash +7,612 B, RAM +5,880 B.**
+**Cost above baseline: Flash +11,576 B, RAM +7,092 B.**
 
 <!-- STAGE-COST:END -->
 
@@ -42,6 +43,7 @@ committed as [`run-report.md`](run-report.md), and rewritten by every stage.
 | Buffered | logging that returns immediately, with the send moved off the logging task | +6,788 | +5,676 |
 | TCP | records the network retransmits instead of dropping, and a send that fails when the collector is gone | +7,320 | +5,856 |
 | Time quality | a timestamp the collector knows how far to trust, and an uptime that tells a reboot from a counter wrap | +7,612 | +5,880 |
+| File store | records that survive a failed send, spooled to disk with a checksum at rest | +11,576 | +7,092 |
 
 *Deltas are bytes above the baseline, which is itself Flash 350,308 B, RAM 111,192 B.*
 

app/syslog/Syslog.c

@@ -9,18 +9,21 @@
 
 #include "Syslog.h"
 
+#include "SolidSyslogBlockStore.h"
 #include "SolidSyslogCircularBuffer.h"
 #include "SolidSyslogConfig.h"
+#include "SolidSyslogCrc16Policy.h"
 #include "SolidSyslogEndpoint.h"
 #include "SolidSyslogEndpointHost.h"
+#include "SolidSyslogFatFsFile.h"
+#include "SolidSyslogFileBlockDevice.h"
 #include "SolidSyslogFreeRtosMutex.h"
 #include "SolidSyslogFreeRtosSysUpTime.h"
 #include "SolidSyslogLwipRawAddress.h"
 #include "SolidSyslogLwipRawMarshal.h"
 #include "SolidSyslogLwipRawResolver.h"
 #include "SolidSyslogLwipRawTcpStream.h"
 #include "SolidSyslogMetaSd.h"
-#include "SolidSyslogNullStore.h"
 #include "SolidSyslogStdAtomicCounter.h"
 #include "SolidSyslogStreamSender.h"
 #include "SolidSyslogTimeQuality.h"
@@ -46,6 +49,10 @@
  * backlog the store is there to hold. */
 #define SYSLOG_BUFFER_RECORDS 8U
 
+/* One "<prefix>NN.log" per block, on the volume the device already mounts. */
+#define SYSLOG_STORE_PREFIX "syslog"
+#define SYSLOG_STORE_BLOCKS 4U
+
 static struct SolidSyslog* s_logger = NULL;
 static uint8_t s_ring[SOLIDSYSLOG_CIRCULAR_BUFFER_RING_BYTES(SYSLOG_BUFFER_RECORDS)];
 
@@ -115,12 +122,19 @@ void Syslog_Start(void)
     s_sd[0] = SolidSyslogMetaSd_Create(&metaConfig);
     s_sd[1] = SolidSyslogTimeQualitySd_Create(SyslogTimeQuality);
 
+    /* Oldest discarded when the ceiling is reached: a device that cannot reach its
+     * collector should keep the newest evidence, not stop logging. */
+    struct SolidSyslogBlockStoreConfig storeConfig = {
+        .BlockDevice = SolidSyslogFileBlockDevice_Create(SolidSyslogFatFsFile_Create(), SYSLOG_STORE_PREFIX, 0U),
+        .MaxBlocks = SYSLOG_STORE_BLOCKS,
+        .DiscardPolicy = SOLIDSYSLOG_DISCARD_POLICY_OLDEST,
+        .SecurityPolicy = SolidSyslogCrc16Policy_Create(),
+    };
+
     struct SolidSyslogConfig config = {
         .Buffer = SolidSyslogCircularBuffer_Create(SolidSyslogFreeRtosMutex_Create(), s_ring, sizeof(s_ring)),
         .Sender = sender,
-        /* No store-and-forward here. The Null object rather than NULL is how
-         * that is said out loud — NULL is reported as a fault. */
-        .Store = SolidSyslogNullStore_Get(),
+        .Store = SolidSyslogBlockStore_Create(&storeConfig),
         /* PROCID stays unset — a bare-metal image has no process. */
         .Clock = SyslogFields_Clock,
         .GetHostname = SyslogFields_Hostname,

measurements/file-store.csv

@@ -0,0 +1,13 @@
+# file-store figures (bytes) — captured by scripts/run.sh (CAPTURE=1).
+# The device reads measurements/Baseline.csv as its frozen baseline and reports current-minus-Baseline.
+flash_text,361252
+flash_data,632
+static_bss,117652
+heap_used,4440
+mbedtls_peak,21276
+mbedtls_free,11492
+lwip_mem_free,7576
+lwip_pbufs_free,14
+stack_log,568
+stack_service,788
+stack_harness,2848

measurements/stages.tsv

@@ -20,3 +20,4 @@ message-cap	Message cap	a bounded record size, so a long message truncates inste
 buffered	Buffered	logging that returns immediately, with the send moved off the logging task
 tcp	TCP	records the network retransmits instead of dropping, and a send that fails when the collector is gone
 time-quality	Time quality	a timestamp the collector knows how far to trust, and an uptime that tells a reboot from a counter wrap
+file-store	File store	records that survive a failed send, spooled to disk with a checksum at rest

run-report.md

@@ -1,4 +1,4 @@
-# solid-syslog-example — run (time-quality)
+# solid-syslog-example — run (file-store)
 
 ## Device (self-measured)
 
@@ -10,16 +10,16 @@
 [device]   first record logged: yes
 [report] --- SolidSyslog cost above baseline (simulated existing application) ---
 [report] key,current,baseline,used_above_baseline
-[report] flash_text,357424,349992,7432
-[report] flash_data,496,316,180
-[report] static_bss,116576,110876,5700
+[report] flash_text,361252,349992,11260
+[report] flash_data,632,316,316
+[report] static_bss,117652,110876,6776
 [report] heap_used,4440,4440,0
-[report] mbedtls_peak,21352,21332,20
-[report] mbedtls_free,11416,11436,-20
+[report] mbedtls_peak,21276,21332,-56
+[report] mbedtls_free,11492,11436,56
 [report] lwip_mem_free,7576,7576,0
-[report] lwip_pbufs_free,13,14,-1
+[report] lwip_pbufs_free,14,14,0
 [report] stack_log,568,120,448
-[report] stack_service,724,52,672
+[report] stack_service,788,52,736
 [report] stack_harness,2848,2840,8
 [report] --- end ---
 [device] ready
@@ -29,7 +29,7 @@
 
 ```text
    text	   data	    bss	    dec	    hex	filename
- 357416	    504	 116576	 474496	  73d80	/w/build/baseline-cross/baseline.elf
+ 361244	    640	 117652	 479536	  75130	/w/build/baseline-cross/baseline.elf
 ```
 
 ## Listeners (proved before the device ran)
@@ -47,23 +47,23 @@
 ## Collector (syslog-ng) received
 
 ```text
-wire   <134>1 2026-07-29T07:42:02.620000Z 10.0.2.15 solid-syslog-example - BOOT [meta sequenceId="1" sysUpTime="362"][timeQuality tzKnown="1" isSynced="0"] device started
-parsed PRIORITY=134 TIMESTAMP=2026-07-29T07:42:02+00:00 HOSTNAME=10.0.2.15 APP_NAME=solid-syslog-example PROCID= MSGID=BOOT STRUCTURED_DATA=[meta sequenceId="1" sysUpTime="362"][timeQuality tzKnown="1" isSynced="0"] MSG=device started
+wire   <134>1 2026-07-29T08:06:15.410000Z 10.0.2.15 solid-syslog-example - BOOT [meta sequenceId="1" sysUpTime="241"][timeQuality tzKnown="1" isSynced="0"] device started
+parsed PRIORITY=134 TIMESTAMP=2026-07-29T08:06:15+00:00 HOSTNAME=10.0.2.15 APP_NAME=solid-syslog-example PROCID= MSGID=BOOT STRUCTURED_DATA=[meta sequenceId="1" sysUpTime="241"][timeQuality tzKnown="1" isSynced="0"] MSG=device started
 ```
 
-## Self-check (vs measurements/time-quality.csv)
+## Self-check (vs measurements/file-store.csv)
 
 ```text
-  OK    flash_text: 357424 (expected 357424, Δ0)
-  OK    flash_data: 496 (expected 496, Δ0)
-  OK    static_bss: 116576 (expected 116576, Δ0)
+  OK    flash_text: 361252 (expected 361252, Δ0)
+  OK    flash_data: 632 (expected 632, Δ0)
+  OK    static_bss: 117652 (expected 117652, Δ0)
   OK    heap_used: 4440 (expected 4440, Δ0)
-  OK    mbedtls_peak: 21352 (expected 21352, Δ0)
-  OK    mbedtls_free: 11416 (expected 11416, Δ0)
+  OK    mbedtls_peak: 21276 (expected 21276, Δ0)
+  OK    mbedtls_free: 11492 (expected 11492, Δ0)
   OK    lwip_mem_free: 7576 (expected 7576, Δ0)
-  OK    lwip_pbufs_free: 13 (expected 13, Δ0)
+  OK    lwip_pbufs_free: 14 (expected 14, Δ0)
   OK    stack_log: 568 (expected 568, Δ0)
-  OK    stack_service: 724 (expected 724, Δ0)
+  OK    stack_service: 788 (expected 788, Δ0)
   OK    stack_harness: 2848 (expected 2848, Δ0)
 ```