Refactor network device handling for flexible device support

Separate network device handling to support various network backends,
such as Slirp, instead of hard-coding the TAP device. The '-netdev'
flag can now be used to specify the network device type, defaulting
to TAP if unspecified. Additionally, packet transfer functions are
now tailored to each network device, enabling more modular and
extensible network device development.

Author: chiangkd

Makefile

@@ -31,6 +31,7 @@ ifeq ($(call has, VIRTIOBLK), 1)
     endif
 endif
 
+NETDEV ?= tap
 # virtio-net
 ENABLE_VIRTIONET ?= 1
 ifneq ($(UNAME_S),Linux)
@@ -39,6 +40,7 @@ endif
 $(call set-feature, VIRTIONET)
 ifeq ($(call has, VIRTIONET), 1)
     OBJS_EXTRA += virtio-net.o
+    OBJS_EXTRA += netdev.o
 endif
 
 BIN = semu
@@ -96,7 +98,7 @@ ext4.img:
 
 check: $(BIN) minimal.dtb $(KERNEL_DATA) $(INITRD_DATA) $(DISKIMG_FILE)
 	@$(call notice, Ready to launch Linux kernel. Please be patient.)
-	$(Q)./$(BIN) -k $(KERNEL_DATA) -c $(SMP) -b minimal.dtb -i $(INITRD_DATA) $(OPTS)
+	$(Q)./$(BIN) -k $(KERNEL_DATA) -c $(SMP) -b minimal.dtb -i $(INITRD_DATA) -n $(NETDEV) $(OPTS)
 
 build-image:
 	scripts/build-image.sh

device.h

@@ -1,5 +1,6 @@
 #pragma once
 
+#include "netdev.h"
 #include "riscv.h"
 #include "virtio.h"
 
@@ -101,7 +102,7 @@ typedef struct {
     uint32_t Status;
     uint32_t InterruptStatus;
     /* supplied by environment */
-    int tap_fd;
+    netdev_t peer;
     uint32_t *ram;
     /* implementation-specific */
     void *priv;
@@ -119,7 +120,7 @@ void virtio_net_write(hart_t *core,
                       uint32_t value);
 void virtio_net_refresh_queue(virtio_net_state_t *vnet);
 
-bool virtio_net_init(virtio_net_state_t *vnet);
+bool virtio_net_init(virtio_net_state_t *vnet, const char *name);
 #endif /* SEMU_HAS(VIRTIONET) */
 
 /* VirtIO-Block */

main.c

@@ -440,19 +440,22 @@ static void handle_options(int argc,
                            char **dtb_file,
                            char **initrd_file,
                            char **disk_file,
+                           char **net_dev,
                            int *hart_count)
 {
-    *kernel_file = *dtb_file = *initrd_file = *disk_file = NULL;
+    *kernel_file = *dtb_file = *initrd_file = *disk_file = *net_dev = NULL;
 
     int optidx = 0;
     struct option opts[] = {
         {"kernel", 1, NULL, 'k'}, {"dtb", 1, NULL, 'b'},
         {"initrd", 1, NULL, 'i'}, {"disk", 1, NULL, 'd'},
-        {"smp", 1, NULL, 'c'},    {"help", 0, NULL, 'h'},
+        {"netdev", 1, NULL, 'n'}, {"smp", 1, NULL, 'c'},
+        {"help", 0, NULL, 'h'},
     };
 
     int c;
-    while ((c = getopt_long(argc, argv, "k:b:i:d:c:h", opts, &optidx)) != -1) {
+    while ((c = getopt_long(argc, argv, "k:b:i:d:n:c:h", opts, &optidx)) !=
+           -1) {
         switch (c) {
         case 'k':
             *kernel_file = optarg;
@@ -466,6 +469,9 @@ static void handle_options(int argc,
         case 'd':
             *disk_file = optarg;
             break;
+        case 'n':
+            *net_dev = optarg;
+            break;
         case 'c':
             *hart_count = atoi(optarg);
             break;
@@ -487,6 +493,9 @@ static void handle_options(int argc,
 
     if (!*dtb_file)
         *dtb_file = "minimal.dtb";
+
+    if (!*net_dev)
+        *net_dev = "tap";
 }
 
 
@@ -509,9 +518,10 @@ static int semu_start(int argc, char **argv)
     char *dtb_file;
     char *initrd_file;
     char *disk_file;
+    char *netdev;
     int hart_count = 1;
     handle_options(argc, argv, &kernel_file, &dtb_file, &initrd_file,
-                   &disk_file, &hart_count);
+                   &disk_file, &netdev, &hart_count);
 
     /* Initialize the emulator */
     emu_state_t emu;
@@ -573,7 +583,7 @@ static int semu_start(int argc, char **argv)
     emu.uart.in_fd = 0, emu.uart.out_fd = 1;
     capture_keyboard_input(); /* set up uart */
 #if SEMU_HAS(VIRTIONET)
-    if (!virtio_net_init(&(emu.vnet)))
+    if (!virtio_net_init(&(emu.vnet), netdev))
         fprintf(stderr, "No virtio-net functioned\n");
     emu.vnet.ram = emu.ram;
 #endif

netdev.c

@@ -0,0 +1,90 @@
+#include <assert.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <linux/if.h>
+#include <linux/if_tun.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+
+#include "netdev.h"
+
+static int net_init_tap();
+static int net_init_user();
+
+static const char *netdev_impl_lookup[] = {
+#define _(dev) [NETDEV_IMPL_##dev] = #dev,
+    SUPPORTED_DEVICES
+#undef _
+        NULL,
+};
+
+static int find_net_dev_idx(const char *net_type, const char **netlookup)
+{
+    if (!net_type)
+        return -1;
+
+    for (int i = 0; netlookup[i]; i++) {
+        if (!strcmp(net_type, netlookup[i]))
+            return i;
+    }
+    return -1;
+}
+
+static int net_init_tap(netdev_t *netdev)
+{
+    net_tap_options_t *tap = (net_tap_options_t *) netdev->op;
+    tap->tap_fd = open("/dev/net/tun", O_RDWR);
+    if (tap->tap_fd < 0) {
+        fprintf(stderr, "failed to open TAP device: %s\n", strerror(errno));
+        return false;
+    }
+
+    /* Specify persistent tap device */
+    struct ifreq ifreq = {.ifr_flags = IFF_TAP | IFF_NO_PI};
+    strncpy(ifreq.ifr_name, "tap%d", sizeof(ifreq.ifr_name));
+    if (ioctl(tap->tap_fd, TUNSETIFF, &ifreq) < 0) {
+        fprintf(stderr, "failed to allocate TAP device: %s\n", strerror(errno));
+        return false;
+    }
+
+    fprintf(stderr, "allocated TAP interface: %s\n", ifreq.ifr_name);
+    assert(fcntl(tap->tap_fd, F_SETFL,
+                 fcntl(tap->tap_fd, F_GETFL, 0) | O_NONBLOCK) >= 0);
+    return 0;
+}
+
+static int net_init_user(netdev_t *netdev)
+{
+    /* TODO: create slirp dev */
+    return 0;
+}
+
+bool netdev_init(netdev_t *netdev, const char *net_type)
+{
+    int dev_idx = find_net_dev_idx(net_type, netdev_impl_lookup);
+    if (dev_idx == -1)
+        return false;
+    netdev->type = dev_idx;
+
+    switch (dev_idx) {
+#define _(dev)                                                           \
+    case NETDEV_IMPL_##dev:                                              \
+        netdev->op = malloc(sizeof(net_##dev##_options_t));              \
+        if (!netdev->op) {                                               \
+            fprintf(stderr, "Failed to allocate memory for %s device\n", \
+                    #dev);                                               \
+            return false;                                                \
+        }                                                                \
+        net_init_##dev(netdev);                                          \
+        break;
+        SUPPORTED_DEVICES
+#undef _
+    default:
+        fprintf(stderr, "unknown network device\n");
+        break;
+    }
+
+    return true;
+}

netdev.h

@@ -0,0 +1,31 @@
+#pragma once
+
+#include <stdbool.h>
+
+/* clang-format off */
+#define SUPPORTED_DEVICES   \
+        _(tap)              \
+        _(user)
+/* clang-format on */
+
+typedef enum {
+#define _(dev) NETDEV_IMPL_##dev,
+    SUPPORTED_DEVICES
+#undef _
+} netdev_impl_t;
+
+typedef struct {
+    int tap_fd;
+} net_tap_options_t;
+
+typedef struct {
+    /* TODO: Implement user option */
+} net_user_options_t;
+
+typedef struct {
+    char *name;
+    netdev_impl_t type;
+    void *op;
+} netdev_t;
+
+bool netdev_init(netdev_t *nedtev, const char *net_type);