This probably should've been done as part of commit d40b343
("rootfs: switch to fd-based handling of mountpoint targets") but it
seems I missed them when doing the rest of the conversions.

This also lets us remove utils.WithProcfd entirely, as well as
pathrs.MkdirAllInRoot.

Signed-off-by: Aleksa Sarai <[email protected]>

Now that MkdirAllInRoot has been removed, we can make MkdirAllInRootOpen
less wordy by renaming it to MkdirAllInRoot. This is a non-functional
change.

Signed-off-by: Aleksa Sarai <[email protected]>

In order to maintain compatibility with previous releases of runc (which
permitted dangling symlinks as path components by permitting
non-existent path components to be treated like real directories) we
have to first do SecureJoin to construct a target path that is
compatible with the old behaviour but has all dangling symlinks (or
other invalid paths like ".." components after non-existent directories)
removed.

This is effectively a more generic verison of commit 3f92552
("rootfs: re-allow dangling symlinks in mount targets") and will let us
remove the need for open-coding SecureJoin workarounds.

Signed-off-by: Aleksa Sarai <[email protected]>

While CreateInRoot supports hallucinating the target path, we do not use
it directly when constructing device inode targets because we need to
have different handling for mknod and bind-mounts.

The solution is to simply have a more generic MkdirAllParentInRoot
helper that MkdirAll's the parent directory of the target path and then
allows the caller to create the trailing component however they like.
(This can be used by CreateInRoot internally as well!)

Signed-off-by: Aleksa Sarai <[email protected]>

We intentionally broke this in commit d40b343 ("rootfs: switch to
fd-based handling of mountpoint targets") under the assumption that most
users do not need this feature. Sadly it turns out they do, and so
commit 3f92552 ("rootfs: re-allow dangling symlinks in mount
targets") added a hotfix to re-add this functionality.

This patch adds some much-needed tests for this behaviour, since it
seems we are going to need to keep this for compatibility reasons (at
least until runc v2...).

Co-developed-by: lifubang <[email protected]>
Signed-off-by: Aleksa Sarai <[email protected]>