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As a part of branch-management, aufs maintains all cached inodes,
dentries, and opened files in remounting.
This commits handles the cached dentries by calling the VFS internal
function d_walk().
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

Now aufs becomes mountable with very few features.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

The marker to represent that the directory is opaque (stop digging
down the branch stack) is implemented as a special whiteout.

See also the document in previous commit.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

The whiteout represents a logical deletion.
Although the document in this commit mentioned about rmdir(2) and
rename(2) for dir, this commit doesn't contain such functions. They will
be added in later commits.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

For details, see previous commit.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

The generation of iinfo and dinfo inherit sbinfo's.
Also iinfo generation tracks the branch inode's generation to test the
matching after the branch management.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

The structure is very similar to aufs inode info (in previous commit).
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>