nixos/modules/fileSystems/default.nix

inputs:
{
	options.nixos.fileSystems = let inherit (inputs.lib) mkOption types; in
	{
		mount =
		{
			# device = mountPoint;
			vfat = mkOption { type = types.attrsOf types.nonEmptyStr; };
			# device.subvol = mountPoint;
			btrfs = mkOption { type = types.attrsOf (types.attrsOf types.nonEmptyStr); };
		};
		decrypt.auto = mkOption { type = types.attrsOf (types.submodule { options =
		{
			mapper = mkOption { type = types.nonEmptyStr; };
			ssd = mkOption { type = types.bool; default = false; };
			before = mkOption { type = types.nullOr (types.listOf types.nonEmptyStr); };
		}; }); };
		mdadm = mkOption { type = types.nullOr types.str; };
		swap = mkOption { type = types.listOf types.nonEmptyStr; };
		resume = mkOption { type = types.nullOr (types.str or (types.submodule { options =
			{ device = mkOption { type = types.nonEmptyStr; }; offset = mkOption { type = types.ints.unsigned; }; }; })); };
		rollingRootfs = mkOption { type = types.nullOr (types.submodule { options =
		{
			device = mkOption { type = types.nonEmptyStr; };
			path = mkOption { type = types.nonEmptyStr; };
		}; }); };
	};
	config = let inherit (inputs.lib) mkMerge mkIf; inherit (inputs.localLib) stripeTabs; in mkMerge
	[
		# mount.vfat
		{
			fileSystems = builtins.listToAttrs (builtins.map
				(device: { name = device.value; value = { device = device.name; fsType = "vfat"; }; })
				(inputs.localLib.attrsToList inputs.config.nixos.fileSystems.mount.vfat));
		}
		# mount.btrfs
		{
			fileSystems = builtins.listToAttrs (builtins.concatLists (builtins.map
				(
					device: builtins.map
						(
							subvol:
							{
								name = subvol.value;
								value =
								{
									device = device.name;
									fsType = "btrfs";
									options = [ "compress-force=zstd:8" "subvol=${subvol.name}" ];
								};
							}
						)
						(inputs.localLib.attrsToList device.value)
				)
				(inputs.localLib.attrsToList inputs.config.nixos.fileSystems.mount.btrfs)));
		}
		# decrypt.auto
		(
			mkIf (inputs.config.nixos.fileSystems.decrypt.auto != null)
			{
				boot.initrd =
				{
					luks.devices = (builtins.listToAttrs (builtins.map
						(
							device:
							{
								name = device.value.mapper;
								value =
								{
									device = device.name;
									allowDiscards = device.value.ssd;
									bypassWorkqueues = device.value.ssd;
									crypttabExtraOpts = [ "fido2-device=auto" "x-initrd.attach" ];
								};
							}
						)
						(inputs.localLib.attrsToList inputs.config.nixos.fileSystems.decrypt.auto)));
					systemd.services =
						let
							createService = device:
							{
								name = "systemd-cryptsetup@${device.name}";
								value =
								{
									before = builtins.map (device: "systemd-cryptsetup@${device}.service") device.value.before;
									overrideStrategy = "asDropin";
								};
							};
						in
							builtins.listToAttrs (builtins.map createService
								(builtins.filter (device: device.value.before != null)
									(inputs.localLib.attrsToList inputs.config.nixos.fileSystems.decrypt.auto)));
				};
			}
		)
		# mdadm
		(
			mkIf (inputs.config.nixos.fileSystems.mdadm != null)
				{ boot.initrd.services.swraid = { enable = true; mdadmConf = inputs.config.nixos.fileSystems.mdadm; }; }
		)
		# swap
		{ swapDevices = builtins.map (device: { device = device; }) inputs.config.nixos.fileSystems.swap; }
		# resume
		(
			mkIf (inputs.config.nixos.fileSystems.resume != null) { boot =
			(
				if builtins.typeOf inputs.config.nixos.fileSystems.resume == "string" then
					{ resumeDevice = inputs.config.nixos.fileSystems.resume; }
				else
				{
					resumeDevice = inputs.config.nixos.fileSystems.resume.device;
					kernelModules = [ "resume_offset=${inputs.config.nixos.fileSystems.resume.offset}" ];
				}
			);}
		)
		# rollingRootfs
		(
			mkIf (inputs.config.nixos.fileSystems.rollingRootfs != null)
			{
				boot.initrd.systemd.services.roll-rootfs =
				{
					wantedBy = [ "local-fs-pre.target" ];
					after = [ "cryptsetup.target" "systemd-hibernate-resume.slice" ];
					before = [ "local-fs-pre.target" ];
					unitConfig.DefaultDependencies = false;
					serviceConfig.Type = "oneshot";
					script = let inherit (inputs.config.nixos.fileSystems.rollingRootfs) device path; in stripeTabs
					"
						mount ${device} /mnt -m
						if [ -f /mnt${path}/current/.timestamp ]
						then
							mv /mnt${path}/current /mnt${path}/$(cat /mnt${path}/current/.timestamp)
						fi
						btrfs subvolume create /mnt${path}/current
						echo $(date '+%Y%m%d%H%M%S') > /mnt${path}/current/.timestamp
						umount /mnt
					";
				};
			}
		)
	];
}

# Disable CoW for VM image and database:
# sudo chattr +C images
# zstd:15 cause sound stuttering
# From btrfs wiki: 1-3 are real-time, 4-8 slower with improved compression,
#	 9-15 try even harder though the resulting size may not be significantly improved.
# https://btrfs.readthedocs.io/en/latest/Compression.html
# sudo btrfs filesystem resize -50G /nix
# sudo cryptsetup status root
# sudo cryptsetup -b 3787456512 resize root
# sudo cfdisk /dev/nvme1n1p3