QEMU check hardcodes filename OVMF_CODE.fd

[gibmat]

On a Debian sid system, Incus 0.4 fails to properly detect that QEMU is available as a backend. This is caused by a hardcoded check for the file OVMF_CODE.fd (driver_qemu.go line 8309).

Beginning with trixie, Debian's ovmf package only ships the 4M images, which include "_4M" in their file names.

I've come up with the following patch that mimics other bits of code in driver_qemu.go to dynamically determine the correct firmware file. This would essentially be the third copy of the same logic in that file, so I didn't submit a PR because it feels like there should be some refactoring as well.

diff --git a/internal/server/instance/drivers/driver_qemu.go b/internal/server/instance/drivers/driver_qemu.go
index 242364a8c..55eb4ffdc 100644
--- a/internal/server/instance/drivers/driver_qemu.go
+++ b/internal/server/instance/drivers/driver_qemu.go
@@ -8306,7 +8306,27 @@ func (d *qemu) checkFeatures(hostArch int, qemuPath string) (map[string]any, err
 	}
 
 	if d.architectureSupportsUEFI(hostArch) {
-		qemuArgs = append(qemuArgs, "-drive", fmt.Sprintf("if=pflash,format=raw,readonly=on,file=%s", filepath.Join(d.ovmfPath(), "OVMF_CODE.fd")))
+		// Determine expected firmware.
+		firmwares := ovmfGenericFirmwares
+		if util.IsTrue(d.expandedConfig["security.csm"]) {
+			firmwares = ovmfCSMFirmwares
+		} else if util.IsTrueOrEmpty(d.expandedConfig["security.secureboot"]) {
+			firmwares = ovmfSecurebootFirmwares
+		}
+
+		var ovmfCode string
+		for _, firmware := range firmwares {
+			if util.PathExists(filepath.Join(d.ovmfPath(), firmware.code)) {
+				ovmfCode = firmware.code
+				break
+			}
+		}
+
+		if ovmfCode == "" {
+			return nil, fmt.Errorf("Unable to locate matching firmware: %+v", firmwares)
+		}
+
+		qemuArgs = append(qemuArgs, "-drive", fmt.Sprintf("if=pflash,format=raw,readonly=on,file=%s", filepath.Join(d.ovmfPath(), ovmfCode)))
 	}
 
 	var stderr bytes.Buffer

[stgraber]

checkFeatures is a function which is called once on daemon startup to validate that QEMU is functional and detect some QEMU capabilities. It's not tied to any particular instance's config so we don't need that much logic in there.

I think I'll just put in a simple loop to try to find "any" firmware it can use.