feat(hwdb): install hwdb on demand when module is needed

[pvalena]

Changes

Adding a module to install hwdb. Further extensions might make only selected part of hwdb installable, to save space. The module is not included by default.

Including the module adds 2MB of compressed data (on Fedora, the file has 12MB).

hwdb is needed in case of custom HW, like a keyboard/mouse or various interfaces.

Original PR: https://github.com/dracutdevs/dracut/pull/1681 Downstream Bug: https://bugzilla.redhat.com/show_bug.cgi?id=1968118

Please note that hwdb.bin is similarly installed by systemd-udevd, which could instead pull in this module as dependency.

Checklist

• [x] I have tested it locally
• [ ] I have reviewed and updated any documentation if relevant
• [ ] I am providing new code and test(s) for it

[LaszloGombos]

I like and support this approach.

Note that the downstream issue would not be resolved unless somehow hwdb.d/20-net-ifname.hwdb also gets installed into the initramfs.

Is that outside of the scope of this PR (perhaps it should be) ?

[dtardon]

Note that the downstream issue would not be resolved unless somehow hwdb.d/20-net-ifname.hwdb also gets installed into the initramfs.

No, that's not needed. .hwdb files are not used directly; they must first be compiled into hwdb.bin, which is a binary format optimized for fast lookup. The compilation (udevadm hwdb --update) is out of scope of udevd. E.g., in rpm world it is likely done in %post (or %posttrans) of any package that installs a .hwdb file. Hence, dracut only needs to install hwdb.bin file(s).

[pvalena]

Note that the downstream issue would not be resolved unless somehow hwdb.d/20-net-ifname.hwdb also gets installed into the initramfs.

No, that's not needed. .hwdb files are not used directly; they must first be compiled into hwdb.bin, which is a binary format optimized for fast lookup. The compilation (udevadm hwdb --update) is out of scope of udevd. E.g., in rpm world it is likely done in %post (or %posttrans) of any package that installs a .hwdb file. Hence, dracut only needs to install hwdb.bin file(s).

Exactly. I've just confirmed: https://gist.github.com/pvalena/873bed9e9eb749f127ca7f60c330dd3d

[pvalena]

+    # The alternative location is preferred, as we can consider it being user
+    # configuration.

IOW first looks in /usr and then in /etc. I don't know what systemd-hwdb behaviour is, it might be best to mimic it. Either way I see having hwdb.bin in both locations (or installing it) undesirable.