9p client truncates modified time nanoseconds field to zero when setting it

[mvondev]

Version

Microsoft Windows [Version 10.0.22000.258]

WSL Version

• WSL 2
• WSL 1

Kernel Version

5.10.60.1

Distro Version

Debian 11.0

Other Software

'touch' utility from the Debian distro's Coreutils package (version 8.32).

Repro Steps

Assume the current user is named fred. All steps are performed in the directory C:\Users\fred\Documents.

Reason for the choice of directory: it is in an NTFS partition which supports a timestamp resolution of 10^-7 seconds.
Steps to follow:

1. Launch Debian Linux and get a bash prompt.
2. Enter cd /mnt/c/Users/fred/Documents.
3. Enter touch newfile to create a new file.
4. Enter stat newfile to get the timestamps of the new file. Here is a sample output:

  File: newfile
  Size: 0               Blocks: 0          IO Block: 4096   regular empty file
Device: 41h/65d Inode: 3659174697380631  Links: 1
Access: (0777/-rwxrwxrwx)  Uid: ( 1000/   wiser)   Gid: ( 1000/   wiser)
Access: 2021-10-21 13:18:53.270571800 +0800
Modify: 2021-10-21 13:18:53.270571800 +0800
Change: 2021-10-21 13:18:53.270571800 +0800
 Birth: -

5. Using this file as a reference file, create another by entering touch anothernewfile -r newfile.
6. Get its timestamps via stat anothernewfile. Here is a sample output:

  File: anothernewfile
  Size: 0               Blocks: 0          IO Block: 4096   regular empty file
Device: 41h/65d Inode: 4785074604233393  Links: 1
Access: (0777/-rwxrwxrwx)  Uid: ( 1000/   wiser)   Gid: ( 1000/   wiser)
Access: 2021-10-21 13:18:53.000000000 +0800
Modify: 2021-10-21 13:18:53.000000000 +0800
Change: 2021-10-21 13:23:15.413922200 +0800
 Birth: -

Expected Behavior

Both stat commands should output timestamps in a resolution of 10^-7 second.

Actual Behavior

The second stat command shows that the second touch command truncate the 'Access' and 'Modify' timestamps to the nearest second.

Diagnostic Logs

No response

[mvondev]

For your information, truncation also happens if you supply a high-resolution timestamp to touch via the -d switch.

[mvondev]

Truncation does not happen inside a VirtualBox VM running Debian Linux.

[mmusenbr]

Hi stumbled over that problem from an issue I had with wildfly and docker in WSL2 and boiled it down to the timestamp issues as well.
It seems filesystems mounted via p9fs support nanosecond timestamp precision in general, eg if accessed via openat-syscalls, but if timestamps are modified via utimensat (and maybe others) the nanoseconds precision is ignored and only the seconds are set.

So this is not only related to 'touch' and definitely not only to the reference file.

@lkydev maybe we can get in touch ;) , because maybe to update the title/description to reflect the broader range of that issue.

[mmusenbr]

I gave it a little more checking. I see the issue only in WSL2 with directories mounted as drvfs via 9p. On WSL I did not see the issue. I created a small C program, which is able to show the difference. Inside WSL install gcc and run gcc -o mod_test <test_file>.c and then ./mod_test /mnt/c/Users/Public/testfile.

michael@WSL2:~$ gcc -o mod_test modified_time_set_test.c
michael@WSL2:~$ ./mod_test /mnt/c/Users/Public/testfile
Creating file '/mnt/c/Users/Public/testfile'
Successfully created file '/mnt/c/Users/Public/testfile'
Setting modified time of '/mnt/c/Users/Public/testfile' to 1635494440.123456800
Reading modified time of '/mnt/c/Users/Public/testfile' is 1635494440.000000000

michael@WSL2:~$ ./mod_test ~/testfile
Creating file '/home/michael/testfile'
Successfully created file '/home/michael/testfile'
Setting modified time of '/home/michael/testfile' to 1635494753.123456800
Reading modified time of '/home/michael/testfile' is 1635494753.123456800

whereas running the same on WSL1 I get the following output:

michael@WSL1:~$ ./mod_test /mnt/c/Users/Public/testfile
Creating file '/mnt/c/Users/Public/testfile'
Successfully created file '/mnt/c/Users/Public/testfile'
Setting modified time of '/mnt/c/Users/Public/testfile' to 1635494846.123456800
Reading modified time of '/mnt/c/Users/Public/testfile' is 1635494846.123456800

[mvondev]

Hi again I ran your program and basically got the same outputs: timestamp truncation occurred on WSL2 but not on WSL1.

[benhillis]

Thanks for posting, I have a repro and I'm attempting to root cause. May be an issue with the 9p client in the Linux kernel since I'm seeing the messages on the host and the modified time nanoseconds field is zero. Will update when I find out more.

[benhillis]

Yes, we have confirmed this is an issue with the Linux kernels 9p client code. We are working on a fix.

[microsoft-github-policy-service]

This issue has been automatically closed since it has not had any activity for the past year. If you're still experiencing this issue please re-file this as a new issue or feature request.

Thank you!