misc/57945: makefs: msdos filesystems with label not reproducible

[jbglaw%lug-owl.de@localhost]

>Number:         57945
>Category:       misc
>Synopsis:       makefs: msdos filesystems with label not reproducible
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    misc-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Feb 18 15:35:00 +0000 2024
>Originator:     Jan-Benedict Glaw
>Release:        current
>Organization:
>Environment:
>Description:
Hi!

I'm working towards getting NetBSD builds reproducible. One issue I face is `makefs` creating/poupulating MSDOS/VFAT filesystems. They're nearly reproducible, but not quite.

While `makefs` has options to create reproducible filesystems (most outstanding are `-T <timestamp>` and `-o volume_id=<n>` (for `-t msdos`), the `-T` timestamp seems to be ignored in the case when there's a volume label (`-o volume_label=<name>`) supplied. That volume label seems to be stored like a filename entry, but it doesn't get the `-T` time set.
>How-To-Repeat:
# Reproducible case:

mkdir __content__
cp /netbsd __content__
makefs -s 100m -t msdos -o volume_label=NETBSD,volume_id=$((0x4711)) -T 1708256777 makefs1.img __content__
sleep 5
makefs -s 100m -t msdos -o volume_label=NETBSD,volume_id=$((0x4711)) -T 1708256777 makefs2.img __content__
sleep 5
makefs -s 100m -t msdos -o                     volume_id=$((0x4711)) -T 1708256777 makefs3.img __content__
sleep 5
makefs -s 100m -t msdos -o                     volume_id=$((0x4711)) -T 1708256777 makefs4.img __content__


sha256 makefs?.img
SHA256 (makefs1.img) = dd4be3ab580bb187a6a0e28cad8f11ccef73ceee6ea4bfc4d1fbdf5b60e88661
SHA256 (makefs2.img) = 3e49d1532e565a737cd06ea2035b098594b6fbefd4323a66eb8533f5115a1a97
SHA256 (makefs3.img) = 37d4bdfb9c5b04a543f46c046cf97139a25f510234da32e6e0f787618d2d5e40
SHA256 (makefs4.img) = 37d4bdfb9c5b04a543f46c046cf97139a25f510234da32e6e0f787618d2d5e40


If the `-o` option (in conjunction with `-t msdos` sets a `volume_label`, its timestamp is taken from current time. Using `fatcat` (had it around on a Linux box), you can actually have a look at the FS label and its timestamp (although that should have been gotten its time from `-T`):

jbglaw@lili:~$ for i in makefs?.img; do echo === $i ===; fatcat $i -l /; echo; done
=== makefs1.img ===
Listing path /
Directory cluster: 0
f 18/2/2024 15:25:42  NETBSD                                             c=0 s=0 (0B)
f 18/2/2024 11:46:16  netbsd (NETBSD)                                    c=12345 s=29579584 (28.2093M)

=== makefs2.img ===
Listing path /
Directory cluster: 0
f 18/2/2024 15:25:48  NETBSD                                             c=0 s=0 (0B)
f 18/2/2024 11:46:16  netbsd (NETBSD)                                    c=12345 s=29579584 (28.2093M)

=== makefs3.img ===
Listing path /
Directory cluster: 0
f 18/2/2024 11:46:16  netbsd (NETBSD)                                    c=12345 s=29579584 (28.2093M)

=== makefs4.img ===
Listing path /
Directory cluster: 0
f 18/2/2024 11:46:16  netbsd (NETBSD)                                    c=12345 s=29579584 (28.2093M)


The NetBSD kernel image OTOH has a properly set timestamp in all four images.
>Fix:
Not yet known. `makefs` uses code from usr.sbin/newfs_msdos and it _seems_ to properly set the timestamp option (and it actually works for copied content), but it seems to not work for the FS label.