Clean up virtio-net TAP option handling

Remove the trailing space from the vnet help text, reject unsupported
virtio-net backends, and avoid repeated virtio-net options when only
one virtio-net device is supported.

At this stage only the TAP backend is accepted. The user-mode backend
will be enabled later when SLIRP support is added.

Also remove the unnecessary device index increment after adding the
virtio-net DTB node, since no later device uses the incremented value

Author: Charlie-Tsai1123

.ci/test-netdev.sh .ci/netdev.sh.ci/test-netdev.sh renamed to .ci/netdev.sh

@@ -139,7 +139,7 @@ static void print_usage(const char *filename)
         "(default read and write). This option may be specified "
         "multiple times for multiple block devices\n"
         "  -x vrng : enable virtio-rng device\n"
-        "  -x vnet:<backend>: use <backend> as virtio-net backend interface \n"
+        "  -x vnet:<backend>: use <backend> as virtio-net backend interface\n"
         "  -b <bootargs> : use customized <bootargs> for the kernel\n"
 #endif
         "  -d [filename]: dump registers as JSON to the "
@@ -201,6 +201,11 @@ static bool parse_args(int argc, char **args)
                     return false;
                 }
                 opt_virtio_net_backend = optarg + 5; /* strlen("vnet:") */
+                if (strcmp(opt_virtio_net_backend, "tap")) {
+                    rv_log_error("unsupported virtio-net backend: %s",
+                                 opt_virtio_net_backend);
+                    return false;
+                }
             } else if (!strcmp("vrng", optarg)) {
                 opt_virtio_rng = true;
             } else {

src/main.c

@@ -531,7 +531,6 @@ static void load_dtb(char **ram_loc, vm_attr_t *attr)
             uint32_t irq = cpu_to_fdt32(new_irq);
             assert(fdt_setprop(dtb_buf, subnode, "interrupts", &irq,
                                sizeof(irq)) == 0);
-            dev_idx++;
         }
     }