distro/rhel8: gce-specific platform override

The gceX86 platform embeds the X86 platform and overrides the
GetPackages() method to exclude the grub2-pc package.

The gce image is built as UEFI only, does not include 'grub2-pc', but we
enable BIOS in the platform config for all the other side-effects: grub
config options and grub2.inst stage.

See the image type documentation for more information:
d12d9674d6/image-types/rhel8/google-gce.md (rhel-8-byosrhui--rhel-9-byos-image-differences-compared-to-googles-image)

internal/distro/rhel8/distro.go

@@ -281,11 +281,14 @@ func newDistro(name string, minor int) *distribution {
 		imageInstaller(),
 	)
 
-	gceX86Platform := &platform.X86{
-		BIOS:       true,
-		UEFIVendor: rd.vendor,
-		BasePlatform: platform.BasePlatform{
-			ImageFormat: platform.FORMAT_GCE,
+	// TODO: review requirement for platform with overridden packages for GCE
+	gceX86Platform := &gceX86{
+		X86: platform.X86{
+			BIOS:       true,
+			UEFIVendor: rd.vendor,
+			BasePlatform: platform.BasePlatform{
+				ImageFormat: platform.FORMAT_GCE,
+			},
 		},
 	}
 

internal/distro/rhel8/gce.go

@@ -4,6 +4,7 @@ import (
 	"github.com/osbuild/osbuild-composer/internal/common"
 	"github.com/osbuild/osbuild-composer/internal/distro"
 	"github.com/osbuild/osbuild-composer/internal/osbuild"
+	"github.com/osbuild/osbuild-composer/internal/platform"
 	"github.com/osbuild/osbuild-composer/internal/rpmmd"
 )
 
@@ -302,3 +303,25 @@ func gceRhuiPackageSet(t *imageType) rpmmd.PackageSet {
 		},
 	}.Append(gceCommonPackageSet(t))
 }
+
+// gceX86 embeds the X86 platform and overrides the GetPackages() method to
+// exclude the grub2-pc package.
+// See the image type documentation for more information:
+// https://github.com/osbuild/osbuild-composer/blob/d12d9674d6293f2c374a66ba2c4fac102633d360/image-types/rhel8/google-gce.md#rhel-8-byosrhui--rhel-9-byos-image-differences-compared-to-googles-image
+type gceX86 struct {
+	platform.X86
+}
+
+func (p *gceX86) GetPackages() []string {
+	packages := p.BasePlatform.FirmwarePackages
+
+	packages = append(packages,
+		"dracut-config-generic",
+		"dracut-config-generic",
+		"efibootmgr",
+		"grub2-efi-x64",
+		"shim-x64")
+
+	return packages
+
+}