Since version 0.136 for Debian Buster we have been patching initramfs-tools with Zstd -compression support for Metztli Reiser4 kernels, both Software Framework Release Number (SFRN) 4.0.2

and SFRN 5.1.3, aka 'Metztli Reiser5', as their respective default configurations were modified to Zstd -compression, as well. Recently, notwithstanding, Zstd -compression support has finally been officially enabled as of initramfs-tools 0.138 and 0.139 by upstream Debian developers.

Zstd -enabled initramfs-tools 0.139 has been tested in Metztli Reiser4 for AMD Epyc/Ryzen customized for Google Compute Engine (GCE), which eight(8) core / 32 Gig RAM development instance -- seen at the top snapshot -- is running a Metztli Reiser4 cloud kernel.

Evidently, not only have we backported initramfs-tools 0.139 for Metztli Reiser4 projects but earlier a minor patch in Bug 971270 was applied and the package built, as well:
initramfs-tools-core_0.139+nmu1_all.deb
initramfs-tools_0.139+nmu1_all.deb

The resulting initramfs-tools 0.139 package was tested in a VirtualBox 6.1.16 -- built from source -- which hosted an older reiser4  instance without the Zstd package installed.

Accordingly, I had to first change the older Debian release information¹:

Shell

Then, after upgrading some packages, I installed my newly built initramfs-tools 0.139 packages, as root, all in a single line:

Shell

Subsequently, observing the red underline and thick arrow, we can verify that Zstd is correctly identified as missing:

Well, the message will be helpful for those Linux enthusiasts who have preexisting non-reiser4 kernels and subsequently download and install any of Metztli Reiser4 releases --as initramfs-tools 0.139 will be automagically fetched and installed during subsequent releases.

References:
¹ Switch Debian 10 RC release to stable

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