[LU-12272] Support renameat2() with RENAME_NOREPLACE flag

Related — Mon, 21 Oct 2019 16:47:15 +0000

This is related to a previous ticket LU-11557 and is also about renameat2(), but actually I think it is even more important so I decided to open a separate ticket.

It would be nice to have support for renameat2() with RENAME_NOREPLACE in Lustre.

Currently, when renameat2 is called with this flag, Lustre doesn't perform the rename: it either returns errno=EINVAL if the destination file doesn't exist, or we got errno=EEXIST if the destination file already exists (the latter is expected). We see the same behavior with other filesystems that also don't support renameat2() flags.

Reproducer:

[sthiell@sh-ln08 login /fir/users/sthiell]$ cat renameat2.c 
#include <errno.h>
#include <stdio.h>
#include <unistd.h>
#include <linux/fs.h>
#include <sys/syscall.h>

int main()
{
  int ret;

  ret = syscall(SYS_renameat2, 0, "/fir/users/sthiell/file1", 0, "/fir/users/sthiell/file2", RENAME_NOREPLACE);
  fprintf(stderr, "renameat2 ret=%d errno=%d (%m)\n", ret, errno, errno);
  return ret;
}


[sthiell@sh-ln08 login /fir/users/sthiell]$ gcc -o renameat2 renameat2.c
[sthiell@sh-ln08 login /fir/users/sthiell]$ rm file1 file2
rm: cannot remove ‘file1’: No such file or directory
rm: cannot remove ‘file2’: No such file or directory
[sthiell@sh-ln08 login /fir/users/sthiell]$ touch file1
[sthiell@sh-ln08 login /fir/users/sthiell]$ ./renameat2
renameat2 ret=-1 errno=22 (Invalid argument)
[sthiell@sh-ln08 login /fir/users/sthiell]$ ls file*
file1
[sthiell@sh-ln08 login /fir/users/sthiell]$ touch file2
[sthiell@sh-ln08 login /fir/users/sthiell]$ ls -i file*
144117284070328763 file1 144117284070328764 file2
[sthiell@sh-ln08 login /fir/users/sthiell]$ ./renameat2
renameat2 ret=-1 errno=17 (File exists)
[sthiell@sh-ln08 login /fir/users/sthiell]$ ls -i file*
144117284070328763 file1 144117284070328764 file2

A local filesystem, here XFS, has the expected behavior:

[sthiell@sh-ln08 login /tmp]$ rm file1 file2
[sthiell@sh-ln08 login /tmp]$ touch file1
[sthiell@sh-ln08 login /tmp]$ ls -i file*
1075302339 file1
[sthiell@sh-ln08 login /tmp]$ ./renameat2 
renameat2 ret=0 errno=0 (Success)
[sthiell@sh-ln08 login /tmp]$ ls -i file*
1075302339 file2
[sthiell@sh-ln08 login /tmp]$ touch file1
[sthiell@sh-ln08 login /tmp]$ ls -i file*
1075302340 file1  1075302339 file2
[sthiell@sh-ln08 login /tmp]$ ./renameat2 
renameat2 ret=-1 errno=17 (File exists)
[sthiell@sh-ln08 login /tmp]$ ls -i file*
1075302340 file1  1075302339 file2

There are multiple use cases that I can think for this feature. Our particular use-case for this is to ensure that when multiple renames are done to the same destination file, only the first one would actually succeed and the others would fail with EEXIST. As of today, subsequent renames always override the destination file. Thanks for considering this feature in a future version of Lustre. Happy to discuss this at LUG next week!

Whamcloud Community JIRA

[LU-12272] Support renameat2() with RENAME_NOREPLACE flag