tarfs: Correctly track link count.

[des]

Summary

Sponsored by: Juniper Networks, Inc.
Sponsored by: Klara, Inc.

[des]

buggy, will resubmit

[des]

Now it works

[kib]

sys/fs/tarfs/tarfs_vfsops.c

745

What protects other->nlink during the increment? Could two calls to tarfs_alloc_one() executed in parallel, targeting the same dst node?

Or even, what protects other itself? For instance, could unmount occur in parallel with the tarfs_alloc_one()?

[des]

sys/fs/tarfs/tarfs_vfsops.c

745

tarfs_alloc_one() is called sequentially during mount, and tarfs_free_node() is called sequentially during unmount or while cleaning up after a failed mount.