makefs: Honor -T timestamps when creating images from mtree manifests

[bnovkov]

Summary

makefs backends rely on the fsnode structure to derive most
of the information about the underlying filesystem objects.
Depending on how the image is built, the fsnode structures
are initialized in the walk_dir or read_mtree functions.
However, read_mtree fails to take timestamps passed by -T into account,
leading to nonreproducible images in backends that do not check for -T.
Fix this and make -T backend-agnostic by adding an appropriate check
in read_mtree_keywords while making sure that mtree entries can
still override -T timestamps.

PR: 285630
Sponsored by: Klara, Inc.
Sponsored by: The FreeBSD Foundation

[markj]

This looks like a much nicer solution.

Does this mean we can remove references to stampst in the backends, e.g., ffs_build_dinode2()?

usr.sbin/makefs/mtree.c

728

[bnovkov]

Address @markj 's comments.

[bnovkov]

In D49531#1129628, @markj wrote:

Does this mean we can remove references to stampst in the backends, e.g., ffs_build_dinode2()?

Yes, I think ffs and msdos have stampst checks and I plan on removing them in a separate commit (along with adding appropriate tests for each backend).

[emaste]

We need to make sure that all four combinations work -- mtree mode / directory scan, -T / no -T

[emaste]

There are three possible timestamps of interest:

1. As stored in the filesystem
2. Specified in a mtree file
3. Overridden timestamp for reproducible builds (cmdline arg or SOURCE_DATE_EPOCH)

In this list higher numbered timestamps should take priority over lower ones.

[bnovkov]

Address @emaste 's comments - mtree timestamps will now no longer override the default timestamp passed by -T.

[kevans]

usr.sbin/makefs/makefs.8

262

I would've perhaps instead changed this to note that they're explicitly ignored if a default timestamp is provided.