The subvolume and the mount point are independent issues. For example, I have a subvolume named @ as root volume: (file-system (device "/dev/mapper/hd") (mount-point "/") (type "btrfs") (options "compress=lzo,ssd,subvol=@")) It also appears that the subvolume name must be prepended to the path as if it just was an ordinary directory (grub.cfg): … linux /@/gnu/store/… … I could not yet confirm this from documentation, but it works like that for me. (I semi-manually edit the generated grub.cfg currently.) So, additionally to stripping the mount point, the subvolume needs to be prepended (grub.scm): (let ((kernel (prepend-subvol device-subvol (strip-mount-point device-mount-point kernel))) (initrd (prepend-subvol device-subvol (strip-mount-point device-mount-point initrd)))) …) This would mean that the menu-entry structure needs the subvol information. However, I wouldn't want to parse this from the options field in the file-system entry, so I'd propose allowing a list there, maybe like this: (file-system (device "/dev/mapper/hd") (mount-point "/") (type "btrfs") (options '(("compress" . "lzo") "ssd" ("subvol" . "@")))) On the other hand, it might be surprising that declaring the options like this would work for subvols, while using a string doesn't, especially when some older documentation/blogs/gists is still hanging around on the internet, so maybe it would be necessary to parse the options anyway (to this list structure). I'm lacking experience in guix and guile, so making this work and submit a patch will take me some time. Do you think this is sensible? -- Svante von Erichsen GPG fingerprint: A78A D4FB 762F A922 A495 57E8 2649 9081 6E61 20DE