Forget about an inode
The nlookup parameter indicates the number of lookups previously performed on this inode.
If the filesystem implements inode lifetimes, it is recommended that inodes acquire a single reference on each lookup, and lose nlookup references on each forget.
The filesystem may ignore forget calls, if the inodes don't need to have a limited lifetime.
On unmount it is not guaranteed, that all referenced inodes will receive a forget message.
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