feat(driver/net): 实现Loopback网卡接口 (#845)

* 初步实现loopback设备

user/apps/test_lo/.gitignore

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+/target
+Cargo.lock
+/install/

user/apps/test_lo/Cargo.toml

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+[package]
+name = "test_lo"
+version = "0.1.0"
+edition = "2021"
+description = "测试lo网卡功能"
+authors = [ "smallc <2628035541@qq.com>" ]
+

user/apps/test_lo/Makefile

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+TOOLCHAIN=
+RUSTFLAGS=
+
+ifdef DADK_CURRENT_BUILD_DIR
+# 如果是在dadk中编译，那么安装到dadk的安装目录中
+	INSTALL_DIR = $(DADK_CURRENT_BUILD_DIR)
+else
+# 如果是在本地编译，那么安装到当前目录下的install目录中
+	INSTALL_DIR = ./install
+endif
+
+ifeq ($(ARCH), x86_64)
+	export RUST_TARGET=x86_64-unknown-linux-musl
+else ifeq ($(ARCH), riscv64)
+	export RUST_TARGET=riscv64gc-unknown-linux-gnu
+else 
+# 默认为x86_86，用于本地编译
+	export RUST_TARGET=x86_64-unknown-linux-musl
+endif
+
+run:
+	RUSTFLAGS=$(RUSTFLAGS) cargo $(TOOLCHAIN) run --target $(RUST_TARGET)
+
+build:
+	RUSTFLAGS=$(RUSTFLAGS) cargo $(TOOLCHAIN) build --target $(RUST_TARGET)
+
+clean:
+	RUSTFLAGS=$(RUSTFLAGS) cargo $(TOOLCHAIN) clean --target $(RUST_TARGET)
+
+test:
+	RUSTFLAGS=$(RUSTFLAGS) cargo $(TOOLCHAIN) test --target $(RUST_TARGET)
+
+doc:
+	RUSTFLAGS=$(RUSTFLAGS) cargo $(TOOLCHAIN) doc --target $(RUST_TARGET)
+
+fmt:
+	RUSTFLAGS=$(RUSTFLAGS) cargo $(TOOLCHAIN) fmt
+
+fmt-check:
+	RUSTFLAGS=$(RUSTFLAGS) cargo $(TOOLCHAIN) fmt --check
+
+run-release:
+	RUSTFLAGS=$(RUSTFLAGS) cargo $(TOOLCHAIN) run --target $(RUST_TARGET) --release
+
+build-release:
+	RUSTFLAGS=$(RUSTFLAGS) cargo $(TOOLCHAIN) build --target $(RUST_TARGET) --release
+
+clean-release:
+	RUSTFLAGS=$(RUSTFLAGS) cargo $(TOOLCHAIN) clean --target $(RUST_TARGET) --release
+
+test-release:
+	RUSTFLAGS=$(RUSTFLAGS) cargo $(TOOLCHAIN) test --target $(RUST_TARGET) --release
+
+.PHONY: install
+install:
+	RUSTFLAGS=$(RUSTFLAGS) cargo $(TOOLCHAIN) install --target $(RUST_TARGET) --path . --no-track --root $(INSTALL_DIR) --force

user/apps/test_lo/README.md

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+# test-lo 
+
+lo网卡功能测试程序
+
+## 测试过程：
+
+通过创建一个UDP套接字，然后发送一条消息到本地回环地址127.0.0.1（lo网卡），再接收并验证这条消息，以此来测试lo网卡的功能。期望发送的消息和接收到的消息是完全一样的。通过日志输出查看测试是否成功。

user/apps/test_lo/src/main.rs

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+use std::net::UdpSocket;
+use std::str;
+
+fn main() -> std::io::Result<()> {
+    let socket = UdpSocket::bind("127.0.0.1:34254")?;
+    socket.connect("127.0.0.1:34254")?;
+
+    let msg = "Hello, loopback!";
+    socket.send(msg.as_bytes())?;
+
+    let mut buf = [0; 1024];
+    let (amt, _src) = socket.recv_from(&mut buf)?;
+
+    let received_msg = str::from_utf8(&buf[..amt]).expect("Could not read buffer as UTF-8");
+
+    println!("Sent: {}", msg);
+    println!("Received: {}", received_msg);
+
+    assert_eq!(
+        msg, received_msg,
+        "The sent and received messages do not match!"
+    );
+
+    Ok(())
+}