cloud-hypervisor: add platformOEMStrings option

Cloud-hypervisor only supports a single --platform argument with comma-separated
options. This commit adds proper handling for platform configuration:

- Add platformOEMStrings option for passing OEM strings in a structured way
- Introduce extractOptValues helper function to extract and remove command-line
  options from argument lists
- Parse any --platform arguments from extraArgs and merge them with configured
  platform options

The extractOptValues function enables proper handling of --platform arguments
in extraArgs while avoiding conflicts with the internally generated --platform
option.

Author: Ramblurr

lib/default.nix

@@ -78,4 +78,59 @@ rec {
     import ./macvtap.nix {
       inherit microvmConfig hypervisorConfig lib;
     };
+
+  /*
+    extractOptValues - Extract and remove all occurrences of a command-line option and its values from a list of arguments.
+
+    Description:
+      This function searches for a specified option flag in a list of command-line arguments,
+      extracts ALL associated values, and returns both the values and a filtered list with
+      all occurrences of the option flag and its values removed. The order of all other
+      arguments is preserved. Uses tail recursion to process the argument list.
+
+    Parameters:
+      optFlag :: String | [String] - The option flag(s) to search for. Can be:
+                                     - A single string (e.g., "-platform")
+                                     - A list of strings (e.g., ["-p" "-platform"])
+                                     All matching flags and their values are extracted
+      extraArgs :: [String] - A list of command-line arguments
+
+    Returns:
+      {
+        values :: [String] - List of all values associated with matching flags (empty list if none found)
+        args :: [String] - The input list with all matched flags and their values removed
+      }
+
+    Examples:
+      # Extract single occurrence:
+      extractOptValues "-platform" ["-vnc" ":0" "-platform" "linux" "-usb"]
+      => { values = ["linux"]; args = ["-vnc" ":0" "-usb"]; }
+
+      # Extract multiple occurrences:
+      extractOptValues "-platform" ["-a" "a" "-b" "b" "-c" "c" "-b" "b2"]
+      => { values = ["b" "b2"]; args = ["-b" "b" "-c" "c"]; }
+
+      # Extract with multiple flag aliases:
+      extractOptValues ["-p" "-platform"] ["-p" "short" "-vnc" ":0" "-platform" "long" "-usb"]
+      => { values = ["short" "long"]; args = ["-vnc" ":0" "-usb"]; }
+
+      # Degenerate case with no matches:
+      extractOptValues ["-p" "-platform"] ["-vnc" ":0" "-usb"]
+      => { values = []; args = ["-vnc" ":0" "-usb"]; }
+  */
+  extractOptValues = optFlag: extraArgs:
+    let
+      flags = if builtins.isList optFlag then optFlag else [optFlag];
+
+      processArgs = args: values: acc:
+        if args == [] then
+          { values = values; args = acc; }
+        else if (builtins.elem (builtins.head args) flags) && (builtins.length args) > 1 then
+          # Found one of the option flags, skip it and its value
+          processArgs (builtins.tail (builtins.tail args)) (values ++ [(builtins.elemAt args 1)]) acc
+        else
+          # Not the option we're looking for, keep this element
+          processArgs (builtins.tail args) values (acc ++ [(builtins.head args)]);
+    in
+      processArgs extraArgs [] [];
 }

lib/runners/cloud-hypervisor.nix

@@ -6,8 +6,9 @@
 
 let
   inherit (pkgs) lib;
+  inherit (import ../. { inherit (pkgs) lib; }) extractOptValues;
   inherit (microvmConfig) vcpu mem balloon initialBalloonMem deflateOnOOM hotplugMem hotpluggedMem user interfaces volumes shares socket devices hugepageMem graphics storeDisk storeOnDisk kernel initrdPath;
-  inherit (microvmConfig.cloud-hypervisor) platformOEMStrings extraPlatformOpts extraArgs;
+  inherit (microvmConfig.cloud-hypervisor) platformOEMStrings extraArgs;
 
   kernelPath = {
     x86_64-linux = "${kernel.dev}/vmlinux";
@@ -96,7 +97,9 @@ let
 
   oemStringValues = (lib.optionals supportsNotifySocket ["io.systemd.credential:vmm.notify_socket=vsock-stream:2:8888"]) ++ platformOEMStrings;
   oemStringOptions = lib.optionals  (oemStringValues != [])  ["oem_strings=[${lib.concatStringsSep "," oemStringValues}]"];
-  platformOps = lib.concatStringsSep "," (oemStringOptions ++ extraPlatformOpts);
+  extraArgsWithoutPlatform = (extractOptValues "--platform" extraArgs).args;
+  userPlatformOpts = (extractOptValues "--platform" extraArgs).values;
+  platformOps = lib.concatStringsSep "," (oemStringOptions ++ userPlatformOpts);
 in {
   inherit tapMultiQueue;
 
@@ -226,7 +229,7 @@ in {
           usb = throw "USB passthrough is not supported on cloud-hypervisor";
         }.${bus}) devices
       )
-    ) + " " + lib.escapeShellArgs extraArgs;
+    ) + " " + lib.escapeShellArgs extraArgsWithoutPlatform;
 
   canShutdown = socket != null;
 

nixos-modules/microvm/options.nix

@@ -519,24 +519,17 @@ in
       type = with types; listOf str;
       default = [];
       description = ''
-      Extra arguments to pass to cloud-hypervisor's --platform oem_strings= argument.
+        Extra arguments to pass to cloud-hypervisor's --platform oem_strings= argument.
 
-      All the oem strings will be concatenated with a comma (,) and wrapped in oem_string=[].
-      '';
-      example = literalExpression /* nix */ ''
-      [ "io.systemd.credential:APIKEY=supersecret" ]
-      '';
-    };
-    cloud-hypervisor.extraPlatformOpts = mkOption {
-      type = with types; listOf str;
-      default = [];
-      description = ''
-      Extra arguments to pass to cloud-hypervisor's --platform argument.
-      All --platform args will be concatended with a comma (,).
-      '';
-      example = literalExpression /* nix */ ''
-      [ "uuid=<dmi_device_uuid>" ]
+        All the oem strings will be concatenated with a comma (,) and wrapped in oem_string=[].
+
+        The resulting string will be combined with any --platform options in
+        `config.microvm.cloud-hypervisor.extraArgs` and passed as a single
+        --platform option to cloud-hypervisor
       '';
+      example = lib.literalExpression /* nix */ ''
+          [ "io.systemd.credential:APIKEY=supersecret" ]
+        '';
     };
 
     cloud-hypervisor.extraArgs = mkOption {