org.osbuild.grub2.iso.legacy: Add grub2 setup for booting BIOS ISO

This is the BIOS version of the grub2 iso stage. It installs the config
file and copies over the grub2 modules to /boot/grub2/

stages/org.osbuild.grub2.iso

@@ -7,6 +7,7 @@ import sys
 import osbuild.api
 
 # The main grub2 configuration file template. Used for UEFI.
+# NOTE: Changes to this should also be applied to the org.osbuild.grub2.iso.legacy stage
 GRUB2_EFI_CFG_TEMPLATE = """
 function load_video {
   insmod efi_gop

stages/org.osbuild.grub2.iso.legacy

@@ -0,0 +1,90 @@
+#!/usr/bin/python3
+import os
+import shutil
+import string
+import sys
+
+import osbuild.api
+
+# The main grub2 configuration file template. Used for BIOS.
+# NOTE: Changes to this should also be applied to the org.osbuild.grub2.iso stage
+GRUB2_CFG_TEMPLATE = """
+function load_video {
+  insmod all_video
+}
+
+load_video
+set gfxpayload=keep
+insmod gzio
+insmod part_gpt
+insmod ext2
+insmod chain
+
+set timeout=${timeout}
+### END /etc/grub.d/00_header ###
+
+search --no-floppy --set=root -l '${isolabel}'
+
+### BEGIN /etc/grub.d/10_linux ###
+menuentry 'Install ${product} ${version}' --class fedora --class gnu-linux --class gnu --class os {
+	linux ${kernelpath} ${root} quiet
+	initrd ${initrdpath}
+}
+menuentry 'Test this media & install ${product} ${version}' --class fedora --class gnu-linux --class gnu --class os {
+	linux ${kernelpath} ${root} rd.live.check quiet
+	initrd ${initrdpath}
+}
+submenu 'Troubleshooting -->' {
+	menuentry 'Install ${product} ${version} in basic graphics mode' --class fedora --class gnu-linux --class gnu --class os {
+		linux ${kernelpath} ${root} nomodeset quiet
+		initrd ${initrdpath}
+	}
+	menuentry 'Rescue a ${product} system' --class fedora --class gnu-linux --class gnu --class os {
+		linux ${kernelpath} ${root} inst.rescue quiet
+		initrd ${initrdpath}
+	}
+	menuentry 'Boot first drive' --class fedora --class gnu-linux --class gnu --class os {
+		chainloader (hd0)+1
+	}
+}
+"""
+
+
+def main(root, options):
+    name = options["product"]["name"]
+    version = options["product"]["version"]
+    isolabel = options["isolabel"]
+    kdir = options["kernel"].get("dir", "/images/pxeboot")
+    kopts = options["kernel"].get("opts")
+    cfg = options.get("config", {})
+    timeout = cfg.get("timeout", 60)
+
+    grub2dir = os.path.join(root, "boot", "grub2")
+    os.makedirs(grub2dir, exist_ok=True)
+
+    # grub2 modules
+    moduledir = os.path.join(grub2dir, "i386-pc")
+    shutil.copytree("/usr/lib/grub/i386-pc", moduledir, dirs_exist_ok=True)
+
+    print(f"kernel dir at {kdir}")
+
+    tplt = string.Template(GRUB2_CFG_TEMPLATE)
+    data = tplt.safe_substitute({
+        "version": version,
+        "product": name,
+        "kernelpath": os.path.join(kdir, "vmlinuz"),
+        "initrdpath": os.path.join(kdir, "initrd.img"),
+        "isolabel": isolabel,
+        "root": " ".join(kopts),
+        "timeout": timeout
+    })
+
+    config = os.path.join(grub2dir, "grub.cfg")
+    with open(config, "w", encoding="utf8") as cfg:
+        cfg.write(data)
+
+
+if __name__ == '__main__':
+    args = osbuild.api.arguments()
+    ret = main(args["tree"], args["options"])
+    sys.exit(ret)

stages/org.osbuild.grub2.iso.legacy.meta.json

@@ -0,0 +1,66 @@
+{
+  "summary": "Install a grub config and supporting files, suitable for a BIOS booting ISO",
+  "description": [],
+  "schema_2": {
+    "options": {
+      "additionalProperties": false,
+      "required": [
+        "product",
+        "kernel",
+        "isolabel"
+      ],
+      "properties": {
+        "product": {
+          "type": "object",
+          "additionalProperties": false,
+          "required": [
+            "name",
+            "version"
+          ],
+          "properties": {
+            "name": {
+              "type": "string"
+            },
+            "version": {
+              "type": "string"
+            }
+          }
+        },
+        "kernel": {
+          "type": "object",
+          "required": [
+            "dir"
+          ],
+          "properties": {
+            "dir": {
+              "type": "string"
+            },
+            "opts": {
+              "description": "Array options to append to the kernel command",
+              "type": "array",
+              "items": {
+                "type": "string"
+              }
+            }
+          }
+        },
+        "isolabel": {
+          "type": "string"
+        },
+        "config": {
+          "description": "Configuration options for grub itself",
+          "type": "object",
+          "additionalProperties": false,
+          "properties": {
+            "timeout": {
+              "description": "Timeout in seconds",
+              "type": "integer",
+              "minimum": 0,
+              "default": 60
+            }
+          }
+        }
+      }
+    }
+  }
+}