Record networking and DMA development progress

Add the current OS source tree, build scripts, system image layout, and development notes covering DMA page allocation, e1000 bring-up, net API dispatch, and DHCP work in progress.

CODE/UTSM/kernel/net.c

@@ -0,0 +1,73 @@
+#include <utsm/net.h>
+#include <utsm/log.h>
+
+/*
+ * 最小 netdev 注册表：
+ * - 早期 DKM 驱动加载路径是单线程顺序执行，当前无需引入锁，避免在网络底座阶段扩大复杂度。
+ * - 后续进入多核/热插拔后，应在 register/device_info 外围加自旋锁或 RCU 风格只读快照。
+ */
+static dkm_net_device_desc g_net_devices[DKM_NET_MAX_DEVICES];
+static u32 g_net_device_count;
+
+void net_init(void) {
+    g_net_device_count = 0;
+    log_info("[NET] registry init");
+}
+
+static int net_register_device_impl(const dkm_net_device_desc *desc) {
+    if (!desc || !desc->name) return -1;
+    if (g_net_device_count >= DKM_NET_MAX_DEVICES) return -2;
+
+    u32 index = g_net_device_count++;
+    g_net_devices[index] = *desc;
+
+    log_info("[NET] device registered");
+    log_info(desc->name);
+    log_hex64("[NET] index=", index);
+    log_hex64("[NET] flags=", desc->flags);
+    return (int)index;
+}
+
+static u32 net_device_count_impl(void) {
+    return g_net_device_count;
+}
+
+static int net_device_info_impl(u32 index, dkm_net_device_info *out) {
+    if (!out) return -1;
+    if (index >= g_net_device_count) return -2;
+
+    const dkm_net_device_desc *dev = &g_net_devices[index];
+    out->name = dev->name;
+    for (u32 i = 0; i < 6; i++) {
+        out->mac[i] = dev->mac[i];
+    }
+    out->flags = dev->flags;
+    return 0;
+}
+
+static int net_tx_impl(u32 index, const void *packet, u32 length) {
+    if (index >= g_net_device_count) return -2;
+    const dkm_net_device_desc *dev = &g_net_devices[index];
+    if (!dev->tx) return -3;
+    log_hex64("[NET] tx dispatch fn=", (u64)dev->tx);
+    return dev->tx(dev->ctx, packet, length);
+}
+
+static int net_rx_poll_impl(u32 index, void *buffer, u32 capacity, u32 *out_length) {
+    if (index >= g_net_device_count) return -2;
+    const dkm_net_device_desc *dev = &g_net_devices[index];
+    if (!dev->rx_poll) return -3;
+    return dev->rx_poll(dev->ctx, buffer, capacity, out_length);
+}
+
+static const dkm_net_api g_net_api = {
+    .register_device = net_register_device_impl,
+    .device_count = net_device_count_impl,
+    .device_info = net_device_info_impl,
+    .tx = net_tx_impl,
+    .rx_poll = net_rx_poll_impl
+};
+
+const dkm_net_api *net_get_api(void) {
+    return &g_net_api;
+}