[LU-11557] Implement renameat2() with RENAME_EXCHANGE and RENAME_WHITEOUT

Related — Tue, 19 Sep 2023 10:58:38 +0000

It would be nice to have support for renameat2()'s linux specific flags RENAME_EXCHANGE and RENAME_WHITEOUT so that Lustre could be safely used as a backend to some overlayfs implementations in user space.

For example, the code snippet below works on ext4 and xfs but not on Lustre:

#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <linux/fs.h>
#include <sys/syscall.h>

int main(int argc, char *argv[])
{
  int ret;

  ret = syscall(SYS_renameat2, AT_FDCWD, argv[1], AT_FDCWD, argv[2], RENAME_EXCHANGE);
  if (ret != 0)
    fprintf(stderr, "renameat2(%s, %s) ret=%d, errno=%d\n", argv[1], argv[2], ret, errno);
  return ret;
}

$ renameat2 file1 file2
renameat2(file1, file2) ret=-1 errno=22

Example on ext4:

$ echo file1 > file1
$ echo file2 > file2
$ ./renameat2 file1 file2
renameat2 ret=0 errno=0
$ cat file1
file2
$ cat file2
file1

Thanks!
Stephane

Whamcloud Community JIRA

[LU-11557] Implement renameat2() with RENAME_EXCHANGE and RENAME_WHITEOUT