dummyfs: extended area isn't always zero-filled after truncate/ftruncate

[damianloew]

According to POSIX mentioned area should always be zero-filled after truncating up:

• truncate:

• ftruncate:

• How to reproduce:

  • Run the following program on dummyfs target (tested on imxrt106x) until it fails (should be visible after ~3 runs)

  #include <stdio.h>
  #include <fcntl.h>
  #include <sys/stat.h>
  #include <unistd.h>
  #include <string.h>
  
  #define LINE1 "line1"
  #define FNAME "testfile"
  
  static int fd;
  static char buf[50];
  
  int setup(void)
  {
      /* open a file */
      fd = open(FNAME, O_RDWR | O_CREAT | O_TRUNC, S_IRUSR | S_IWUSR);
      if (fd < 0) {
          fprintf(stderr, "File hasn't been opened correctly\n");
          return -1;
      }
      memset(buf, '\0', sizeof(buf));
  
      return 0;
  }
  
  int teardown(void)
  {
      memset(buf, '\0', sizeof(buf));
      if (fd >= 0) {
          if (close(fd) != 0) {
              fprintf(stderr, "File has't been closed correctly\n");
              return -1;
          }
      }
  
      if (remove(FNAME) != 0) {
          fprintf(stderr, "File has't been removed correctly\n");
          return -1;
      }
  }
  
  int tcase(void)
  {
      struct stat st;
      int datalen = 2 * sizeof(LINE1);
      int ret;
  
      /* alter buf with arbitrary data, because '\0' are going to be stored */
      memset(buf, ' ', sizeof(buf));
  
      /* write LINE1 to the file */
      if ((ret = write(fd, LINE1, sizeof(LINE1))) != sizeof(LINE1)) {
          fprintf(stderr, "All bytes haven't been writte, ret = %d\n", ret);
          return -1;
      }
  
      if (close(fd) != 0) {
          fprintf(stderr, "File has't been closed correctly\n");
          return -1;
      }
  
      /* truncate file length to higher than it already is */
      if (truncate(FNAME, datalen) != 0) {
          fprintf(stderr, "Truncate failed\n");
          return -1;
      }
  
      fd = open(FNAME, O_RDONLY, S_IRUSR);
  
      if (fd < 0) {
          fprintf(stderr, "File hasn't been opened correctly\n");
          return -1;
      }
  
      if ((ret = read(fd, buf, datalen)) != datalen) {
          fprintf(stderr, "All bytes haven't been read, ret = %d\n", ret);
          return -1;
      }
  
      for (int i = 0; i < datalen; i++)
      {
          printf("file[%d] = %c (%d)\n", i, buf[i], buf[i]);
      }
  
      return 0;
  }
  
  int main(void)
  {
      if (setup() < 0) {
          return 1;
      }
      if (tcase() < 0) {
          return 1;
      }
      if (teardown() < 0) {
          return 1;
      }
  
          return 0;
  }
  

  • result (some junk output visible):

  

• The same behavior when using ftruncate

• Needed to run test-libc on dummyfs targets

[badochov]

I've done a PR solving this however in my testing on imx6ull I wasn't able to observe this bug even before the fix. https://github.com/phoenix-rtos/phoenix-rtos-filesystems/pull/91

[damianloew]

Thanks! I confirm that the above issue does no longer occur on imxrt106x target (I assume on other dummyfs targets too)