[LU-11017] quota exceeded returned when creating files with root user in directory where setgid is set

• Type: Bug
• Resolution: Fixed
• Priority: Minor
• Fix Version/s: Lustre 2.12.0
• Severity: 3
• Assignee: Wang Shilong (Inactive)
• Reporter: Wang Shilong (Inactive)

Description

Set setgid flag on the directory and set inode hard quota for the gruop.  
# cd /lustre
# mkdir aaa
# chown test1:tes1 aaa
# chmod g+s aaa
# lfs setquota -g test1 -I 4096 /lustre

With test1 group, create many files until quota exceeded occur.  
# su - test1
$ for i in `seq -w 0001 4096`; do touch ${i} ; done
$ exit

Then, with root user, create a directory. It returns quota exceeded error.  
# mkdir bbb
mkdir: cannot create directory ‘bbb’: Disk quota exceeded

reason is Lustre try to check quota for file owner uid, gid and it will skip quota type check if this
quota type id is 0.

For setgid, even root user try touch a file, the file's group id will still inherit from its parents.
So quota check will ignore user quota, but still enforce group quota for the file.

The idea should be Like GPFS or ext4, that we pass CAP_SYS_RESOURCE down and use this
to check whether we should skip quota.