Support virtio-console

Makefile

@@ -215,6 +215,27 @@ ifeq ($(call has, VIRTIOGPU), 1)
     OBJS_EXTRA += vgpu-display.o
 endif
 
+# Guest console: UART-8250 or virtio-console
+SEMU_CONSOLE ?= virtio
+SEMU_CONSOLE := $(strip $(SEMU_CONSOLE))
+override ENABLE_UART8250 := 0
+override ENABLE_VIRTIOCONSOLE := 0
+ifeq ($(SEMU_CONSOLE),uart8250)
+    override ENABLE_UART8250 := 1
+else ifeq ($(SEMU_CONSOLE),virtio)
+    override ENABLE_VIRTIOCONSOLE := 1
+else
+    $(error SEMU_CONSOLE must be either uart8250 or virtio)
+endif
+$(call set-feature, UART8250)
+$(call set-feature, VIRTIOCONSOLE)
+
+ifeq ($(call has, UART8250), 1)
+    OBJS_EXTRA += uart.o
+else
+    OBJS_EXTRA += virtio-console.o
+endif
+
 ifneq ($(filter 1,$(call has, VIRTIOGPU) $(call has, VIRTIOINPUT)),)
     OBJS_EXTRA += window-sw.o
 endif
@@ -227,7 +248,7 @@ OBJS := \
 	ram.o \
 	utils.o \
 	plic.o \
-	uart.o \
+	console.o \
 	main.o \
 	aclint.o \
 	coro.o \

README.md

@@ -11,6 +11,8 @@ A minimalist RISC-V system emulator capable of running Linux the kernel and corr
 - Standard SBI, with the timer extension
 - I/O support using VirtIO standard:
     - virtio-blk acquires disk image from the host.
+    - virtio-console provides a paravirtualized console.
+    - virtio-rng provides entropy to the guest.
     - 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:
         - As some unknown issues in guest Linux OS (confirmed in v6.7 and v6.12), you need

configs/linux.config

@@ -834,7 +834,7 @@ CONFIG_SERIAL_CORE_CONSOLE=y
 # CONFIG_NULL_TTY is not set
 # CONFIG_SERIAL_DEV_BUS is not set
 # CONFIG_TTY_PRINTK is not set
-# CONFIG_VIRTIO_CONSOLE is not set
+CONFIG_VIRTIO_CONSOLE=y
 # CONFIG_IPMI_HANDLER is not set
 CONFIG_HW_RANDOM=y
 CONFIG_HW_RANDOM_VIRTIO=y

console.c

@@ -0,0 +1,59 @@
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <termios.h>
+#include <unistd.h>
+
+#include "console.h"
+
+#define CONSOLE_ESCAPE 1 /* Ctrl-a */
+
+static struct termios saved_termios;
+static int terminal_fd = -1;
+static int output_fd = -1;
+static bool escape_pending;
+
+static void host_console_restore(void)
+{
+    if (terminal_fd >= 0)
+        tcsetattr(terminal_fd, TCSANOW, &saved_termios);
+}
+
+void host_console_setup(int in_fd, int out_fd)
+{
+    struct termios termios;
+
+    output_fd = out_fd;
+    if (!isatty(in_fd) || tcgetattr(in_fd, &saved_termios) < 0)
+        return;
+
+    termios = saved_termios;
+    termios.c_lflag &= ~(ICANON | ECHO | ISIG);
+    if (tcsetattr(in_fd, TCSANOW, &termios) < 0)
+        return;
+
+    terminal_fd = in_fd;
+    atexit(host_console_restore);
+}
+
+ssize_t host_console_read(int fd, void *buf, size_t len)
+{
+    ssize_t nread = read(fd, buf, len);
+    uint8_t *bytes = buf;
+
+    if (nread <= 0)
+        return nread;
+
+    for (ssize_t i = 0; i < nread; i++) {
+        if (escape_pending && bytes[i] == 'x') {
+            if (output_fd >= 0) {
+                ssize_t written = write(output_fd, "\n", 1);
+                (void) written;
+            }
+            exit(0);
+        }
+        escape_pending = bytes[i] == CONSOLE_ESCAPE;
+    }
+
+    return nread;
+}

console.h

@@ -0,0 +1,7 @@
+#pragma once
+
+#include <stddef.h>
+#include <sys/types.h>
+
+void host_console_setup(int in_fd, int out_fd);
+ssize_t host_console_read(int fd, void *buf, size_t len);

device.h

@@ -50,6 +50,7 @@ void plic_write(hart_t *core,
                 uint32_t value);
 /* UART */
 
+#if SEMU_HAS(UART8250)
 #define IRQ_UART 1
 #define IRQ_UART_BIT (1 << IRQ_UART)
 
@@ -84,7 +85,7 @@ void u8250_write(hart_t *core,
                  uint32_t value);
 void u8250_check_ready(u8250_state_t *uart);
 void u8250_flush_out(u8250_state_t *uart);
-void capture_keyboard_input();
+#endif /* SEMU_HAS(UART8250) */
 
 /* virtio-net */
 
@@ -347,6 +348,57 @@ uint32_t virtio_gpu_register_scanout(virtio_gpu_state_t *vgpu,
                                      uint32_t height);
 #endif /* SEMU_HAS(VIRTIOGPU) */
 
+/* VirtIO-Console */
+
+#if SEMU_HAS(VIRTIOCONSOLE)
+
+#define IRQ_VCONSOLE 10
+#define IRQ_VCONSOLE_BIT (1 << IRQ_VCONSOLE)
+
+typedef struct {
+    uint32_t QueueNum;
+    uint32_t QueueDesc;
+    uint32_t QueueAvail;
+    uint32_t QueueUsed;
+    uint16_t last_avail;
+    bool ready;
+} virtio_console_queue_t;
+
+typedef struct {
+    /* feature negotiation */
+    uint32_t DeviceFeaturesSel;
+    uint32_t DriverFeatures;
+    uint32_t DriverFeaturesSel;
+    /* queue config */
+    uint32_t QueueSel;
+    virtio_console_queue_t queues[2];
+    /* status */
+    uint32_t Status;
+    uint32_t InterruptStatus;
+    /* supplied by environment */
+    uint32_t *ram;
+    int in_fd;
+    int out_fd;
+} virtio_console_state_t;
+
+void virtio_console_read(hart_t *core,
+                         virtio_console_state_t *vcon,
+                         uint32_t addr,
+                         uint8_t width,
+                         uint32_t *value);
+void virtio_console_write(hart_t *core,
+                          virtio_console_state_t *vcon,
+                          uint32_t addr,
+                          uint8_t width,
+                          uint32_t value);
+void virtio_console_refresh(virtio_console_state_t *vcon);
+void virtio_console_init(virtio_console_state_t *vcon,
+                         uint32_t *ram,
+                         int in_fd,
+                         int out_fd);
+
+#endif /* SEMU_HAS(VIRTIOCONSOLE) */
+
 /* ACLINT MTIMER */
 typedef struct {
     /* A MTIMER device has two separate base addresses: one for the MTIME
@@ -558,7 +610,9 @@ typedef struct {
     uint32_t *disk;
     vm_t vm;
     plic_state_t plic;
+#if SEMU_HAS(UART8250)
     u8250_state_t uart;
+#endif
 #if SEMU_HAS(VIRTIONET)
     virtio_net_state_t vnet;
 #endif
@@ -581,13 +635,16 @@ typedef struct {
 #if SEMU_HAS(VIRTIOGPU)
     virtio_gpu_state_t vgpu;
 #endif
+#if SEMU_HAS(VIRTIOCONSOLE)
+    virtio_console_state_t vconsole;
+#endif
 #if SEMU_HAS(VIRTIOINPUT) || SEMU_HAS(VIRTIOGPU)
     /* 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()' can call 'poll(-1)' and block 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.
+     * waiting for timer or console 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

feature.h

@@ -2,6 +2,14 @@
 
 /* enable/disable (compile time) features in this header */
 
+#ifndef SEMU_FEATURE_VIRTIOCONSOLE
+#define SEMU_FEATURE_VIRTIOCONSOLE 1
+#endif
+
+#ifndef SEMU_FEATURE_UART8250
+#define SEMU_FEATURE_UART8250 0
+#endif
+
 /* virtio-blk */
 #ifndef SEMU_FEATURE_VIRTIOBLK
 #define SEMU_FEATURE_VIRTIOBLK 1