Implement virtio-input for keyboard and mouse

.ci/common.sh

@@ -7,6 +7,9 @@ set -euo pipefail
 MACHINE_TYPE="$(uname -m)"
 OS_TYPE="$(uname -s)"
 
+# Enable SDL headless mode explicitly.
+export SDL_VIDEODRIVER=offscreen
+
 # Cleanup function - kills all semu processes
 cleanup() {
     sleep 1

.ci/test-vinput.sh

@@ -0,0 +1,73 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+. "${SCRIPT_DIR}/common.sh"
+
+# Override timeout for macOS - emulation is significantly slower
+case "${OS_TYPE}" in
+    Darwin)
+        TIMEOUT=1200
+        ;;
+esac
+
+cleanup
+trap cleanup EXIT
+
+# Feature toggles are passed through environment variables, which do not
+# participate in make's normal dependency tracking. Force a rebuild here so
+# one-feature-at-a-time test runs never reuse a stale semu binary.
+make -B semu minimal.dtb
+
+# NOTE: We want to capture the expect exit code and map 
+# it to our MESSAGES array for meaningful error output.
+# Temporarily disable errexit for the expect call.
+set +e
+expect <<'DONE'
+set timeout $env(TIMEOUT)
+spawn make check
+
+# Boot and login
+expect "buildroot login:" { send "root\r" } timeout { exit 1 }
+expect "# "              { send "uname -a\r" } timeout { exit 2 }
+expect "riscv32 GNU/Linux" {}
+
+# ---------------- virtio-input ----------------
+# Require actual event* nodes, not just /dev/input directory existence.
+# Print a concrete status marker that is not present in the echoed command text.
+expect "# " { send "if ls /dev/input/event* >/dev/null 2>&1; then status=OK; else status=BAD; fi; printf \"__EVT_%s__\\n\" \"\$status\"\r" }
+expect {
+  -exact "__EVT_OK__" {}
+  -exact "__EVT_BAD__" { exit 3 }
+  timeout { exit 3 }
+}
+
+expect "# " { send "cat /proc/bus/input/devices | head -20\r" }
+# Emit a shell-expanded status marker so expect cannot match the echoed command.
+expect "# " { send "if grep -qi virtio /proc/bus/input/devices; then status=OK; else status=BAD; fi; printf \"__VPROC_%s__\\n\" \"\$status\"\r" }
+expect {
+  -exact "__VPROC_OK__" {}
+  -exact "__VPROC_BAD__" { exit 3 }
+  timeout { exit 3 }
+}
+DONE
+
+ret="$?"
+set -e  # Re-enable errexit after capturing expect's return code
+
+MESSAGES=(
+  "PASS: headless virtio-input checks"
+  "FAIL: boot/login prompt not found"
+  "FAIL: shell prompt not found"
+  "FAIL: virtio-input basic checks failed (/dev/input/event* or /proc/bus/input/devices)"
+  "FAIL: virtio-input event stream did not produce bytes (needs host->virtio-input injection path)"
+)
+
+if [[ "${ret}" -eq 0 ]]; then
+  print_success "${MESSAGES[0]}"
+  exit 0
+fi
+
+print_error "${MESSAGES[${ret}]:-FAIL: unknown error (exit code ${ret})}"
+exit "${ret}"

.github/actions/setup-semu/action.yml

@@ -14,7 +14,8 @@ runs:
           device-tree-compiler \
           expect \
           libasound2-dev \
-          libudev-dev
+          libudev-dev \
+          libsdl2-dev
 
     - name: Install dependencies (macOS)
       if: runner.os == 'macOS'
@@ -23,4 +24,4 @@ runs:
         HOMEBREW_NO_AUTO_UPDATE: 1
         HOMEBREW_NO_ANALYTICS: 1
       run: |
-        brew install make dtc expect e2fsprogs
+        brew install make dtc expect e2fsprogs sdl2

.github/workflows/main.yml

@@ -73,6 +73,10 @@ jobs:
       run: .ci/test-sound.sh
       shell: bash
       timeout-minutes: 5
+    - name: virtio-input test
+      run: .ci/test-vinput.sh
+      shell: bash
+      timeout-minutes: 5
 
   semu-macOS:
     runs-on: macos-latest
@@ -126,6 +130,10 @@ jobs:
       run: .ci/test-sound.sh
       shell: bash
       timeout-minutes: 20
+    - name: virtio-input test
+      run: .ci/test-vinput.sh
+      shell: bash
+      timeout-minutes: 20
 
   coding_style:
     runs-on: ubuntu-24.04

.gitignore

@@ -11,3 +11,10 @@ rootfs.cpio
 
 # intermediate
 riscv-harts.dtsi
+.smp_stamp
+rootfs_full.cpio
+
+# Build directories
+buildroot/
+linux/
+rootfs/

Makefile

@@ -158,6 +158,31 @@ LDFLAGS += -lm
 # after git submodule.
 .DEFAULT_GOAL := all
 
+# SDL2
+ENABLE_SDL ?= 1
+ifeq (, $(shell which sdl2-config))
+    $(warning No sdl2-config in $$PATH. Check SDL2 installation in advance)
+    override ENABLE_SDL := 0
+endif
+ifeq ($(ENABLE_SDL),1)
+    CFLAGS += $(shell sdl2-config --cflags)
+    LDFLAGS += $(shell sdl2-config --libs)
+else
+    # Disable virtio-input if SDL is not set
+    override ENABLE_VIRTIOINPUT := 0
+endif
+
+# virtio-input
+ENABLE_VIRTIOINPUT ?= 1
+ENABLE_INPUT_DEBUG ?= 0
+CFLAGS += -DSEMU_INPUT_DEBUG=$(ENABLE_INPUT_DEBUG)
+$(call set-feature, VIRTIOINPUT)
+ifeq ($(call has, VIRTIOINPUT), 1)
+    OBJS_EXTRA += virtio-input-event.o
+    OBJS_EXTRA += virtio-input.o
+    OBJS_EXTRA += window-sw.o
+endif
+
 BIN = semu
 all: $(BIN) minimal.dtb
 

README.md

@@ -9,7 +9,7 @@ A minimalist RISC-V system emulator capable of running Linux the kernel and corr
 - UART: 8250/16550
 - PLIC (platform-level interrupt controller): 32 interrupts, no priority
 - Standard SBI, with the timer extension
-- Three types of I/O support using VirtIO standard:
+- Four types of I/O support using VirtIO standard:
     - virtio-blk acquires disk image from the host.
     - virtio-net is mapped as TAP interface.
     - virtio-snd uses [PortAudio](https://github.com/PortAudio/portaudio) for sound playback on the host with one limitations:
@@ -18,6 +18,8 @@ A minimalist RISC-V system emulator capable of running Linux the kernel and corr
           the program cannot write the PCM frames into guest OS ALSA stack.
             - For instance, the following buffer/period size settings on `aplay` has been tested
               with broken and stutter effects yet complete with no any errors: `aplay --buffer-size=32768 --period-size=4096 /usr/share/sounds/alsa/Front_Center.wav`.
+    - virtio-input exposes SDL-backed keyboard and mouse devices to the guest.
+      - You can exit the SDL window by pressing Ctrl+A+G
 
 ## Prerequisites
 

configs/linux.config

@@ -759,7 +759,7 @@ CONFIG_INPUT=y
 #
 # CONFIG_INPUT_MOUSEDEV is not set
 # CONFIG_INPUT_JOYDEV is not set
-# CONFIG_INPUT_EVDEV is not set
+CONFIG_INPUT_EVDEV=y
 # CONFIG_INPUT_EVBUG is not set
 
 #
@@ -1053,7 +1053,7 @@ CONFIG_VIRTIO_ANCHOR=y
 CONFIG_VIRTIO=y
 CONFIG_VIRTIO_MENU=y
 # CONFIG_VIRTIO_BALLOON is not set
-# CONFIG_VIRTIO_INPUT is not set
+CONFIG_VIRTIO_INPUT=y
 CONFIG_VIRTIO_MMIO=y
 # CONFIG_VIRTIO_MMIO_CMDLINE_DEVICES is not set
 # CONFIG_VDPA is not set

device.h

@@ -12,6 +12,9 @@
 #define DTB_SIZE (1 * 1024 * 1024)
 #define INITRD_SIZE (8 * 1024 * 1024)
 
+#define SCREEN_WIDTH 1024
+#define SCREEN_HEIGHT 768
+
 void ram_read(hart_t *core,
               uint32_t *mem,
               const uint32_t addr,
@@ -229,6 +232,67 @@ void virtio_rng_write(hart_t *vm,
 void virtio_rng_init(void);
 #endif /* SEMU_HAS(VIRTIORNG) */
 
+/* VirtIO Input */
+
+#if SEMU_HAS(VIRTIOINPUT)
+
+#define IRQ_VINPUT_KEYBOARD 7
+#define IRQ_VINPUT_KEYBOARD_BIT (1 << IRQ_VINPUT_KEYBOARD)
+
+#define IRQ_VINPUT_MOUSE 8
+#define IRQ_VINPUT_MOUSE_BIT (1 << IRQ_VINPUT_MOUSE)
+
+typedef struct {
+    uint32_t QueueNum;
+    uint32_t QueueDesc;
+    uint32_t QueueAvail;
+    uint32_t QueueUsed;
+    uint16_t last_avail;
+    bool ready;
+} virtio_input_queue_t;
+
+typedef struct {
+    /* feature negotiation */
+    uint32_t DeviceFeaturesSel;
+    uint32_t DriverFeatures;
+    uint32_t DriverFeaturesSel;
+    /* queue config */
+    uint32_t QueueSel;
+    virtio_input_queue_t queues[2];
+    /* status */
+    uint32_t Status;
+    uint32_t InterruptStatus;
+    /* supplied by environment */
+    uint32_t *ram;
+    /* implementation-specific */
+    void *priv;
+} virtio_input_state_t;
+
+void virtio_input_read(hart_t *vm,
+                       virtio_input_state_t *vinput,
+                       uint32_t addr,
+                       uint8_t width,
+                       uint32_t *value);
+
+void virtio_input_write(hart_t *vm,
+                        virtio_input_state_t *vinput,
+                        uint32_t addr,
+                        uint8_t width,
+                        uint32_t value);
+
+void virtio_input_init(virtio_input_state_t *vinput);
+
+/* Drain translated host window events and update guest-visible virtio-input
+ * device state. Must be called from the emulator thread.
+ */
+void virtio_input_drain_host_events(void);
+
+/* Returns true if the device has a pending interrupt. Safe to call from
+ * the emulator thread without holding any lock internally.
+ */
+bool virtio_input_irq_pending(virtio_input_state_t *vinput);
+#endif /* SEMU_HAS(VIRTIOINPUT) */
+
 /* ACLINT MTIMER */
 typedef struct {
     /* A MTIMER device has two separate base addresses: one for the MTIME
@@ -433,6 +497,7 @@ bool virtio_fs_init(virtio_fs_state_t *vfs, char *mtag, char *dir);
 
 /* memory mapping */
 typedef struct {
+    int exit_code;
     bool debug;
     bool stopped;
     uint32_t *ram;
@@ -459,6 +524,24 @@ typedef struct {
 #if SEMU_HAS(VIRTIOFS)
     virtio_fs_state_t vfs;
 #endif
+#if SEMU_HAS(VIRTIOINPUT)
+    virtio_input_state_t vkeyboard;
+    virtio_input_state_t vmouse;
+    /* Use self-pipe trick to unblock the emulator loop when the
+     * window backend has queued work, such as input events or
+     * window shutdown. When all harts are idle, semu_run() calls
+     * poll(-1) and blocks indefinitely waiting for timer or UART
+     * events. The window-event thread has no way to wake that
+     * blocked poll() other than writing to a file descriptor it is
+     * watching.
+     *
+     * wake_fd[0] (read end) is added to pfds[] so poll() monitors it.
+     * wake_fd[1] (write end) is handed to the window backend, which
+     * writes one byte when backend work arrives to make wake_fd[0]
+     * readable and return poll() immediately.
+     */
+    int wake_fd[2];
+#endif
 
     uint32_t peripheral_update_ctr;
 

feature.h

@@ -22,5 +22,10 @@
 #define SEMU_FEATURE_VIRTIOFS 1
 #endif
 
+/* virtio-input */
+#ifndef SEMU_FEATURE_VIRTIOINPUT
+#define SEMU_FEATURE_VIRTIOINPUT 1
+#endif
+
 /* Feature test macro */
 #define SEMU_HAS(x) SEMU_FEATURE_##x