mtime incorrect in fatfs during daylight saving time (IDFGH-7467)

[lbernstone]

Environment

• Development Kit: Custom, but N/A
• Module or chip used: ESP32-C3, likely all
• IDF version (run git describe --tags to find it): v4.4.1
• Build System: Arduino
• Compiler version (run xtensa-esp32-elf-gcc --version to find it): riscv32-esp-elf-gcc8_4_0-esp-2021r2-patch3-linux-amd64
• Operating System: Linux
• Using an IDE?: Yes , arduino just for convenience. No Arduino code included in example
• Power Supply: USB

Problem Description

When a timezone is set with DST, and time is set inside DST, file modified time (mtime) is 3599 seconds off. Weird number, maybe something is supposed to be one hour diff, but isn't multiplied?

Expected Behavior

System time and file written time should be identical

Actual Behavior

22:29:11.888 -> systime: 1653638041
22:29:12.154 -> filetime: 1653641640

Steps to reproduce

#include <vfs_fat_internal.h>
static wl_handle_t hndWl = WL_INVALID_HANDLE;

void setup() {
  Serial.begin(115200);
  delay(2000);
  struct timeval tv = {1653638041, 0};
  settimeofday(&tv, NULL);
  setenv("TZ", "MST7MDT,M3.2.0,M11.1.0", 1);
  tzset();
  Serial.printf("systime: %d\n", time(NULL));
  const esp_vfs_fat_mount_config_t conf = {
      .format_if_mount_failed = true,
      .max_files = 4,
      .allocation_unit_size = CONFIG_WL_SECTOR_SIZE
  };
  esp_vfs_fat_spiflash_mount("/fatfs", "ffat", &conf, &hndWl);
  FILE *tfile = fopen("/fatfs/test", "w");
  fprintf(tfile, "hello");
  fclose(tfile);
  struct stat info;
  stat("/fatfs/test", &info);
  Serial.printf("filetime: %d\n", info.st_mtime);
}
void loop() {delay(-1);}

[igrr]

Thanks for reporting this @lbernstone. I vaguely remember there being some discussion on this before, and some reason why the filesystem works the way it does, but I can't find it right now. We'll investigate this.

The difference is probably indeed one hour (3600 seconds), but FATFS keeps time at 2-second precision, so instead of mtime=1653641641 (exactly 3600 seconds difference) you got 1653641640.

[lbernstone]

Only thing I see in the history is this #1369