Created attachment 190220 [details]
test on tmp filesystem that can be unmounted

When doing an ftruncate+mmap+fsync to a size less than 512 bytes the data never seems to be sync'd properly to disk.

This work fine on the latest 11.1-RELEASE but not the latest 11.1-STABLE. It is also ok if the ftruncate is to the existing file size.

While the mapped changes are visible in the file before an umount, after even a failed umount, the changes are no longer present.


(non-error checked) C code below.

After running the binary, check the contents of the file (eg hd) and it will be all 0xFF. Then, umount the filesystem you are on*. Then check the contents of the file again. It will now be 0x01.

Running extra sync's or fsync's from the command line before the umount doesn't seem to help.

* The umount should fail but still shows the problem. However note it doesn't seem to work with the error given for the root filesystem "/".

I've also attached a script that creates a filesystem to umount

---

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <sys/mman.h>

int
main (int argc, char *argv[])
{
   int fd;
   size_t i, size1, size2;
   char *data;
   char *filename;
   char pattern = 0x01;

   if (argc < 2) {
      fprintf(stderr, "Usage: %s filename size1 size2\n", argv[0]);
      exit(1);
   }

   filename = argv[1];
   size1 = atoi(argv[2]);
   size2 = atoi(argv[3]);

   fd = open(filename, O_RDWR | O_TRUNC | O_CREAT, 0644);
   for (i = 0; i < size1; i++)
      write(fd, &pattern, 1);
   close(fd);

   fd = open(filename, O_RDWR, 0644);
   ftruncate(fd, size2);
   data = mmap(NULL, size2, PROT_READ|PROT_WRITE,MAP_SHARED,fd,0);
   memset(data, 0xFF, size2);
   fsync(fd);

   munmap(data, size2);
   close(fd);
}