flock possibly missing in SMB3 POSIX extensions?

Aurélien Aptel aaptel at suse.com
Fri Feb 26 16:17:51 UTC 2021


While debugging cifs.ko customer issues we found that flock(2) seems to
be impossible to properly emulate using SMB.

On first sight it looks like they could be emulated with SMB locks but
the main difference is that FLOCKs are completely advisory, the application
is free to ignore them and sucessfully do read/write, whereas with SMB
locks WRITE/READ will fail on locked areas.

The flock syscall is avaible on most unixes so it would make sense to
support it I think. Maybe via a special flag for LOCK.

Given the number of options to control locking behaviour in Samba and
given how NFS doesn't support it properly either maybe there are
problems I'm not seeing.

Aurélien Aptel / SUSE Labs Samba Team
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