Add DriveType= setting for qemu root disk device type

Add a new DriveType= setting that allows configuring the device type
used for the root disk when booting a virtual machine with qemu. The
supported types are virtio-blk (default, preserving existing behavior),
virtio-scsi, and nvme.

Previously, the only way to use nvme was by manually adding qemu device
arguments via QemuArgs=. This makes nvme a first-class option.

When Removable= is enabled, the drive type is forced to virtio-scsi
regardless of the DriveType= setting, preserving existing behavior.

Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: brauner

mkosi/config.py

@@ -404,6 +404,12 @@ class Vmm(StrEnum):
     vmspawn = enum.auto()
 
 
+class QemuDiskType(StrEnum):
+    virtio_blk = enum.auto()
+    virtio_scsi = enum.auto()
+    nvme = enum.auto()
+
+
 class Ssh(StrEnum):
     always = enum.auto()
     auto = enum.auto()
@@ -2242,6 +2248,7 @@ class Config:
     vsock_cid: int
     tpm: ConfigFeature
     removable: bool
+    disk_type: QemuDiskType
     firmware: Firmware
     firmware_variables: Optional[Path]
     linux: Optional[str]
@@ -4346,6 +4353,16 @@ def parse_kernel_module_filter_regexp(p: str) -> str:
         compat_names=("QemuRemovable",),
         scope=SettingScope.main,
     ),
+    ConfigSetting(
+        dest="disk_type",
+        name="DiskType",
+        section="Runtime",
+        parse=config_make_enum_parser(QemuDiskType),
+        default=QemuDiskType.virtio_blk,
+        choices=QemuDiskType.choices(),
+        help="Set the disk type for the root disk in the virtual machine",
+        scope=SettingScope.main,
+    ),
     ConfigSetting(
         dest="firmware",
         section="Runtime",
@@ -6121,6 +6138,7 @@ def credential_transformer(
         Network: enum_transformer,
         KeySource: key_source_transformer,
         Vmm: enum_transformer,
+        QemuDiskType: enum_transformer,
         list[UKIProfile]: uki_profile_transformer,
         UnifiedKernelImage: enum_transformer,
         list[ArtifactOutput]: enum_list_transformer,

mkosi/qemu.py

@@ -38,6 +38,7 @@
     Firmware,
     Network,
     OutputFormat,
+    QemuDiskType,
     Ssh,
     Verb,
     VsockCID,
@@ -1201,9 +1202,6 @@ def add_virtiofs_mount(
             sock = stack.enter_context(start_virtiofsd(config, tree.source))
             add_virtiofs_mount(sock, Path("/root/src") / (tree.target or ""), cmdline, credentials)
 
-        if config.output_format in (OutputFormat.disk, OutputFormat.esp):
-            cmdline += ["-device", "virtio-scsi-pci,id=mkosi"]
-
         if config.output_format == OutputFormat.cpio:
             cmdline += ["-initrd", fname]
         elif (
@@ -1216,6 +1214,13 @@ def add_virtiofs_mount(
             cmdline += ["-initrd", initrd]
 
         if config.output_format in (OutputFormat.disk, OutputFormat.esp):
+            disk_type = config.disk_type
+            if config.removable:
+                disk_type = QemuDiskType.virtio_scsi
+
+            if disk_type == QemuDiskType.virtio_scsi:
+                cmdline += ["-device", "virtio-scsi-pci,id=mkosi"]
+
             blockdev = [
                 "driver=raw",
                 "node-name=mkosi",
@@ -1227,13 +1232,23 @@ def add_virtiofs_mount(
                 f"cache.no-flush={yes_no(config.ephemeral)}",
             ]
 
-            device_type = "virtio-blk-pci"
-            if config.removable:
-                device_type = "scsi-hd,device_id=mkosi,removable=on"
+            if disk_type == QemuDiskType.virtio_blk:
+                device = "virtio-blk-pci"
+            elif disk_type == QemuDiskType.virtio_scsi:
+                device = "scsi-hd"
+                if config.removable:
+                    device += ",device_id=mkosi,removable=on"
+            elif disk_type == QemuDiskType.nvme:
+                device = "nvme,serial=mkosi"
+            else:
+                # pyright doesn't do exhaustiveness checking so we need this branch explicitly.
+                die(f"Unexpected disk type: {disk_type}")
+
+            device += ",drive=mkosi,bootindex=1"
 
             cmdline += [
                 "-blockdev", ",".join(blockdev),
-                "-device", f"{device_type},drive=mkosi,bootindex=1",
+                "-device", device,
             ]  # fmt: skip
 
         if config.tpm == ConfigFeature.enabled or (

mkosi/resources/man/mkosi.1.md

@@ -1897,7 +1897,14 @@ boolean argument: either `1`, `yes`, or `true` to enable, or `0`, `no`,
 
 `Removable=`, `--removable=`
 :   Configures whether to attach the image as a removable device when booting
-    a virtual machine. Takes a boolean value. Defaults to `no`.
+    a virtual machine. Takes a boolean value. Defaults to `no`. When enabled,
+    the root disk is always attached as a SCSI device regardless of the
+    `DiskType=` setting.
+
+`DiskType=`, `--disk-type=`
+:   Configures the disk type to use for the root disk when booting a virtual
+    machine. Takes one of `virtio-blk`, `virtio-scsi`, or `nvme`. Defaults to
+    `virtio-blk`.
 
 `Firmware=`, `--firmware=`
 :   Configures the virtual machine firmware to use. Takes one of `uefi`,

tests/test_json.py

@@ -35,6 +35,7 @@
     ManifestFormat,
     Network,
     OutputFormat,
+    QemuDiskType,
     SecureBootSignTool,
     ShimBootloader,
     Ssh,
@@ -166,6 +167,7 @@ def test_config() -> None:
             "Devicetrees": [
                 "freescale/imx8mm-verdin-nonwifi-dev.dtb"
             ],
+            "DiskType": "virtio-blk",
             "Distribution": "fedora",
             "Drives": [
                 {
@@ -482,6 +484,7 @@ def test_config() -> None:
         ],
         dependencies=["dep1"],
         distribution=Distribution.fedora,
+        disk_type=QemuDiskType.virtio_blk,
         drives=[
             Drive("abc", 200, Path("/foo/bar"), "abc,qed", "red", []),
             Drive("abc", 200, None, "", "wcd", []),