NixOS PR 236656 breaks squashfs support

[chkno]

NixOS/nixpkgs#236656 breaks squashfs support, in that it requires the nix store image to be mountable by label and squashfs doesn't support filesystem labels ( plougher/squashfs-tools#59 ).

[chkno]

In practice, erofs doesn't help much: A 2.0G squashfs becomes an 8.1G ext4 or a 5.9G erofs image.

mkfs.erofs has flags for controlling compression settings. Some improvement is probably possible through messing with those.

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A possible route to getting squashfs support back would be to patch the guest's kernel libblkid to add squashfs label support. It needn't be a high-quality patch that upstream would accept. For use cases that only mount one squashfs image, even a dreadful kludge that just hard-codes "nix-store" as the label for all squashfs filesystems would suffice.