Meta: Detect nested KVM support for WSL2 and use that when available

This allows running QEMU inside WSL2 for hosts which have nested KVM
and WSLg support (e.g. Windows 11).

Running QEMU inside the WSL2 VM is slightly slower than running QEMU
on Windows, probably because of how WSLg handles screen updates.

Meta/run.sh

@@ -10,7 +10,8 @@ die() {
 
 #SERENITY_PACKET_LOGGING_ARG="-object filter-dump,id=hue,netdev=breh,file=e1000.pcap"
 
-[ -e /dev/kvm ] && [ -r /dev/kvm ] && [ -w /dev/kvm ] && SERENITY_VIRT_TECH_ARG="-enable-kvm"
+KVM_SUPPORT="0"
+[ -e /dev/kvm ] && [ -r /dev/kvm ] && [ -w /dev/kvm ] && KVM_SUPPORT="1"
 
 [ -z "$SERENITY_BOCHS_BIN" ] && SERENITY_BOCHS_BIN="bochs"
 
@@ -41,10 +42,14 @@ if [ -z "$SERENITY_QEMU_BIN" ]; then
     if command -v wslpath >/dev/null; then
         QEMU_INSTALL_DIR=$(reg.exe query 'HKLM\Software\QEMU' /v Install_Dir /t REG_SZ | grep '^    Install_Dir' | sed 's/    / /g' | cut -f4- -d' ')
         if [ -z "$QEMU_INSTALL_DIR" ]; then
-            die "Could not determine where QEMU for Windows is installed. Please make sure QEMU is installed or set SERENITY_QEMU_BIN if it is already installed."
+            if [ "$KVM_SUPPORT" -eq "0" ]; then
+                die "Could not determine where QEMU for Windows is installed. Please make sure QEMU is installed or set SERENITY_QEMU_BIN if it is already installed."
+            fi
+        else
+            KVM_SUPPORT="0"
+            QEMU_BINARY_PREFIX="$(wslpath -- "${QEMU_INSTALL_DIR}" | tr -d '\r\n')/"
+            QEMU_BINARY_SUFFIX=".exe"
         fi
-        QEMU_BINARY_PREFIX="$(wslpath -- "${QEMU_INSTALL_DIR}" | tr -d '\r\n')/"
-        QEMU_BINARY_SUFFIX=".exe"
     fi
     if command -v "${QEMU_BINARY_PREFIX}qemu-system-x86_64${QEMU_BINARY_SUFFIX}" >/dev/null; then
         SERENITY_QEMU_BIN="${QEMU_BINARY_PREFIX}qemu-system-x86_64${QEMU_BINARY_SUFFIX}"
@@ -56,6 +61,8 @@ if [ -z "$SERENITY_QEMU_BIN" ]; then
     fi
 fi
 
+[ "$KVM_SUPPORT" -eq "1" ] && SERENITY_VIRT_TECH_ARG="-enable-kvm"
+
 [ -z "$SERENITY_KERNEL_CMDLINE" ] && SERENITY_KERNEL_CMDLINE="hello"
 
 [ -z "$SERENITY_RAM_SIZE" ] && SERENITY_RAM_SIZE=512M
@@ -90,6 +97,8 @@ if [ "$installed_major_version" -lt "$SERENITY_QEMU_MIN_REQ_VERSION" ]; then
     die
 fi
 
+NATIVE_WINDOWS_QEMU="0"
+
 if command -v wslpath >/dev/null; then
     case "$SERENITY_QEMU_BIN" in
         /mnt/?/*)
@@ -102,6 +111,8 @@ if command -v wslpath >/dev/null; then
             fi
             [ -z "$SERENITY_QEMU_CPU" ] && SERENITY_QEMU_CPU="max,vmx=off"
             SERENITY_KERNEL_CMDLINE="$SERENITY_KERNEL_CMDLINE disable_virtio"
+            NATIVE_WINDOWS_QEMU="1"
+            ;;
     esac
 fi
 
@@ -115,7 +126,7 @@ fi
 
 if [ "$(uname)" = "Darwin" ]; then
     SERENITY_AUDIO_BACKEND="-audiodev coreaudio,id=snd0"
-elif command -v wslpath >/dev/null; then
+elif [ "$NATIVE_WINDOWS_QEMU" -eq "1" ]; then
     SERENITY_AUDIO_BACKEND="-audiodev dsound,id=snd0"
 elif "$SERENITY_QEMU_BIN" -audio-help 2>&1 | grep -- "-audiodev id=sdl" >/dev/null; then
     SERENITY_AUDIO_BACKEND="-audiodev sdl,id=snd0"
@@ -130,15 +141,15 @@ else
 fi
 
 SERENITY_SCREENS="${SERENITY_SCREENS:-1}"
-if  [ "$SERENITY_SPICE" ]; then
+if [ "$SERENITY_SPICE" ]; then
     SERENITY_QEMU_DISPLAY_BACKEND="${SERENITY_QEMU_DISPLAY_BACKEND:-spice-app}"
-elif command -v wslpath >/dev/null; then
+elif [ "$NATIVE_WINDOWS_QEMU" -eq "1" ]; then
     # QEMU for windows does not like gl=on, so detect if we are building in wsl, and if so, disable it
     # Also, when using the GTK backend we run into this problem: https://github.com/SerenityOS/serenity/issues/7657
     SERENITY_QEMU_DISPLAY_BACKEND="${SERENITY_QEMU_DISPLAY_BACKEND:-sdl,gl=off}"
 elif [ $SERENITY_SCREENS -gt 1 ] && "${SERENITY_QEMU_BIN}" --display help | grep -iq sdl; then
     SERENITY_QEMU_DISPLAY_BACKEND="${SERENITY_QEMU_DISPLAY_BACKEND:-sdl,gl=off}"
-elif ("${SERENITY_QEMU_BIN}" --display help | grep -iq sdl) && (ldconfig -p | grep -iq virglrenderer); then
+elif ! command -v wslpath >/dev/null && ("${SERENITY_QEMU_BIN}" --display help | grep -iq sdl) && (ldconfig -p | grep -iq virglrenderer); then
     SERENITY_QEMU_DISPLAY_BACKEND="${SERENITY_QEMU_DISPLAY_BACKEND:-sdl,gl=on}"
 elif "${SERENITY_QEMU_BIN}" --display help | grep -iq cocoa; then
     # QEMU for OSX seems to only support cocoa