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Use a tempfile / rename for atomic writes in order to prevent dataloss during a HardFault on a repeater #2386

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Use a tempfile / rename for atomic writes in order to prevent dataloss during a HardFault on a repeater #2386

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2ea8687
Use a tempfile / rename for atomic writes in order to prevent datalo…
Apr 24, 2026
cb47439
Don't change the function call but handle the tmp file within a separ…
winnieXY Apr 26, 2026
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22 changes: 19 additions & 3 deletions src/helpers/ClientACL.cpp
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Original file line number Diff line number Diff line change
@@ -1,9 +1,16 @@
#include "ClientACL.h"

static char* getTmpPath(const char* filename) {
static char tmp_filename[32];
snprintf(tmp_filename, sizeof(tmp_filename), "%s.tmp", filename);
return tmp_filename;
}

static File openWrite(FILESYSTEM* _fs, const char* filename) {
#if defined(NRF52_PLATFORM) || defined(STM32_PLATFORM)
_fs->remove(filename);
return _fs->open(filename, FILE_O_WRITE);
char* tmp_filename = getTmpPath(filename);
_fs->remove(tmp_filename);
return _fs->open(tmp_filename, FILE_O_WRITE);
#elif defined(RP2040_PLATFORM)
return _fs->open(filename, "w");
#else
Expand Down Expand Up @@ -54,7 +61,8 @@ void ClientACL::load(FILESYSTEM* fs, const mesh::LocalIdentity& self_id) {

void ClientACL::save(FILESYSTEM* fs, bool (*filter)(ClientInfo*)) {
_fs = fs;
File file = openWrite(_fs, "/s_contacts");
const char* real_path = "/s_contacts";
File file = openWrite(_fs, real_path);
if (file) {
uint8_t unused[2];
memset(unused, 0, sizeof(unused));
Expand All @@ -74,6 +82,14 @@ void ClientACL::save(FILESYSTEM* fs, bool (*filter)(ClientInfo*)) {
if (!success) break; // write failed
}
file.close();

#if defined(NRF52_PLATFORM) || defined(STM32_PLATFORM)
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@ripplebiz ripplebiz Apr 26, 2026

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@oltaco Can you verify that _fs->rename() definitely will work in this case? ie. does the real_path file get overwritten/replaced?

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@oltaco oltaco Apr 26, 2026

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Confirmed, the underlying lfs_rename() call will point the old directory entry for file at the blocks referenced by file.tmp and then remove the directory entry for file.tmp

char* tmp_path = getTmpPath(real_path);
if (!_fs->rename(tmp_path, real_path)) {
_fs->remove(tmp_path);
MESH_DEBUG_PRINTLN("ERROR: ClientACL::save rename failed!");
}
#endif
}
}

Expand Down
15 changes: 13 additions & 2 deletions src/helpers/CommonCLI.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -126,8 +126,12 @@ void CommonCLI::loadPrefsInt(FILESYSTEM* fs, const char* filename) {

void CommonCLI::savePrefs(FILESYSTEM* fs) {
#if defined(NRF52_PLATFORM) || defined(STM32_PLATFORM)
fs->remove("/com_prefs");
File file = fs->open("/com_prefs", FILE_O_WRITE);
// Atomic write: write to temp file, then rename over the real file.
// LittleFS rename() is a single metadata commit -- atomic even on power loss.
const char* tmp_path = "/com_prefs.tmp";
const char* real_path = "/com_prefs";
fs->remove(tmp_path); // clean up any stale temp from previous failed write
File file = fs->open(tmp_path, FILE_O_WRITE);
#elif defined(RP2040_PLATFORM)
File file = fs->open("/com_prefs", "w");
#else
Expand Down Expand Up @@ -183,6 +187,13 @@ void CommonCLI::savePrefs(FILESYSTEM* fs) {
// next: 291

file.close();

#if defined(NRF52_PLATFORM) || defined(STM32_PLATFORM)
if (!fs->rename(tmp_path, real_path)) {
fs->remove(tmp_path);
MESH_DEBUG_PRINTLN("ERROR: savePrefs rename failed!");
}
#endif
}
}

Expand Down
25 changes: 21 additions & 4 deletions src/helpers/RegionMap.cpp
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Original file line number Diff line number Diff line change
@@ -1,6 +1,6 @@
#include "RegionMap.h"
#include <helpers/TxtDataHelpers.h>
#include <SHA256.h>
#include <SHA256.h>

// helper class for region map exporter, we emulate Stream with a safe buffer writer.

Expand Down Expand Up @@ -58,10 +58,17 @@ static const char* skip_hash(const char* name) {
return *name == '#' ? name + 1 : name;
}

static char* getTmpPath(const char* filename) {
static char tmp_filename[32];
snprintf(tmp_filename, sizeof(tmp_filename), "%s.tmp", filename);
return tmp_filename;
}

static File openWrite(FILESYSTEM* _fs, const char* filename) {
#if defined(NRF52_PLATFORM) || defined(STM32_PLATFORM)
_fs->remove(filename);
return _fs->open(filename, FILE_O_WRITE);
char* tmp_filename = getTmpPath(filename);
_fs->remove(tmp_filename);
return _fs->open(tmp_filename, FILE_O_WRITE);
#elif defined(RP2040_PLATFORM)
return _fs->open(filename, "w");
#else
Expand Down Expand Up @@ -115,7 +122,8 @@ bool RegionMap::load(FILESYSTEM* _fs, const char* path) {
}

bool RegionMap::save(FILESYSTEM* _fs, const char* path) {
File file = openWrite(_fs, path ? path : "/regions2");
const char* real_path = path ? path : "/regions2";
File file = openWrite(_fs, real_path);
if (file) {
uint8_t pad[128];
memset(pad, 0, sizeof(pad));
Expand All @@ -139,6 +147,15 @@ bool RegionMap::save(FILESYSTEM* _fs, const char* path) {
}
}
file.close();

#if defined(NRF52_PLATFORM) || defined(STM32_PLATFORM)
char* tmp_path = getTmpPath(real_path);
if (!_fs->rename(tmp_path, real_path)) {
_fs->remove(tmp_path);
MESH_DEBUG_PRINTLN("ERROR: RegionMap::save rename failed!");
return false;
}
#endif
return true;
}
return false; // failed
Expand Down