# Copyright (C) 2005-2019 Junjiro R. Okajima

Lookup in a Branch
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Since aufs has a character of sub-VFS (see Introduction), it operates
lookup for branches as VFS does. It may be a heavy work. But almost all
lookup operation in aufs is the simplest case, ie. lookup only an entry
directly connected to its parent. Digging down the directory hierarchy
is unnecessary. VFS has a function lookup_one_len() for that use, and
aufs calls it.

When a branch is a remote filesystem, aufs basically relies upon its
->d_revalidate(), also aufs forces the hardest revalidate tests for
them.
For d_revalidate, aufs implements three levels of revalidate tests. See
"Revalidate Dentry and UDBA" in detail.