Question about inode security blob

Hi,

I'm trying to learn the security blob infrastructure for my future LSM development.

Unlike other blobs, I found inode security blob has a special pattern. I couldn’t find useful information on the web so I think this mail list is the most appropriate place to ask this question.

The BPF and SELinux will check whether the inode->i_security is NULL before use
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/include/linux/bpf_lsm.h#n35
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/security/selinux/include/objsec.h#n164

But for smack, it doesn't do such a check
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/security/smack/smack.h#n347
Is this because smack_set_mnt_opts() already does the NULL check at
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/security/smack/smack_lsm.c#n784 ?

Also, I wonder in which situation will the inode->i_security be NULL?

Thanks, and I hope I could make my contributions to LSM soon.

Best,
Fan