[LU-18791] report overflowed nlink counter correctly for striped dirs.

• Type: Bug
• Resolution: Fixed
• Priority: Minor
• Fix Version/s: Lustre 2.17.0
• Labels: patch
• Severity: 3
• Assignee: Alexander Zarochentsev
• Reporter: Alexander Zarochentsev

Description

on ldiskfs backend, if shards of a striped dir have more than ~64k subdirectories , the reported nlink attribute for the striped directory is incorrect:

[root@rocky tests]# ../utils/lfs mkdir -c 2 /mnt/lustre/dir-c2
[root@rocky tests]# for x in {0..160}; do for y in {0..999} ; do mkdir /mnt/lustre/dir-c2/$x-$y; done; echo .. ${x}k ..; done
.. 0k ..
.. 1k ..
.. 2k ..
.. 3k ..
.. 4k ..
...
.. 160k ..
[root@rocky tests]# stat /mnt/lustre/dir-c2
  File: /mnt/lustre/dir-c2
  Size: 7815168   	Blocks: 15280      IO Block: 1048576 directory
Device: 2c54f966h/743766374d	Inode: 144115205289279489  Links: 0
Access: (0755/drwxr-xr-x)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2025-03-10 19:50:11.000000000 +0300
Modify: 2025-03-10 19:53:07.000000000 +0300
Change: 2025-03-10 19:53:07.000000000 +0300
 Birth: 2025-03-10 19:50:11.000000000 +0300
[root@rocky tests]# 

as you see, the nlink count is 0.