lkl: add libslirp network backend for user-mode networking

.github/workflows/ci.yml

@@ -67,6 +67,7 @@ jobs:
             python-pip
             dosfstools
             mingw-w64-x86_64-ccache
+            mingw-w64-x86_64-libslirp
 
       - name: Checkout
         if: runner.os == 'Linux'
@@ -108,7 +109,7 @@ jobs:
         if: runner.os == 'Linux'
         run: |
           sudo apt update -y
-          sudo apt install -y ccache libjsmn-dev libfuse3-dev
+          sudo apt install -y ccache libjsmn-dev libfuse3-dev libslirp-dev
       - name: Install clang toolchain
         if: runner.os == 'Linux'
         run: |

tools/lkl/Makefile.autoconf

@@ -63,6 +63,11 @@ define virtio_net_vde
   LDLIBS += $(shell pkg-config --libs vdeplug)
 endef
 
+define virtio_net_slirp
+  $(call set_autoconf_var,VIRTIO_NET_SLIRP,y)
+  LDLIBS += $(shell pkg-config --libs slirp)
+endef
+
 define zpoline_conf
   $(eval zpoline_dir=$(abspath $(srctree)/$(1)))
   $(if $(strip $(foreach f, $(zpoline_dir), $(wildcard $(f)/libzpoline.so))),$(call set_autoconf_var,ZPOLINE_DIR,$(zpoline_dir)))
@@ -83,6 +88,7 @@ define posix_host
   $(if $(filter $(1),elf64-littleriscv),$(call riscv64_host))
   $(if $(filter yes,$(dpdk)),$(call virtio_net_dpdk))
   $(if $(filter yes,$(vde)),$(call virtio_net_vde))
+  $(if $(strip $(call find_include,slirp/libslirp.h)),$(call virtio_net_slirp))
   $(if $(strip $(call find_include,fuse3/fuse.h)),$(call set_autoconf_var,FUSE,y))
   $(if $(strip $(call find_include,archive.h)),$(call set_autoconf_var,ARCHIVE,y))
   $(if $(strip $(call find_include,linux/if_tun.h)),$(call set_autoconf_var,VIRTIO_NET_MACVTAP,y))
@@ -96,6 +102,7 @@ define nt64_host
   $(call set_autoconf_var,NEEDS_LARGP,y)
   $(call set_autoconf_var,VIRTIO_NET,y)
   $(call set_autoconf_var,NT64,y)
+  $(if $(strip $(shell pkg-config --cflags slirp 2>/dev/null)),$(call virtio_net_slirp))
   CFLAGS += -Wl,--enable-auto-image-base -Wl,--image-base -Wl,0x10000000 \
 	 -Wl,--out-implib=$(OUTPUT)liblkl.dll.a -Wl,--export-all-symbols \
 	 -Wl,--enable-auto-import

tools/lkl/include/lkl.h

@@ -844,6 +844,62 @@ lkl_netdev_wintap_create(const char *ifparams)
 }
 #endif
 
+/**
+ * lkl_netdev_slirp_create - create slirp net_device for the virtio net backend
+ *
+ * Provides user-mode TCP/IP networking without requiring root privileges.
+ * Guest network is 10.0.2.0/24 with gateway at 10.0.2.2 and DNS at 10.0.2.3.
+ * Use lkl_netdev_slirp_add_hostfwd() for port forwarding from host to guest.
+ */
+#ifdef LKL_HOST_CONFIG_VIRTIO_NET_SLIRP
+struct lkl_netdev *lkl_netdev_slirp_create(void);
+
+/**
+ * lkl_netdev_slirp_add_hostfwd - add port forwarding from host to guest
+ *
+ * @nd - netdev returned by lkl_netdev_slirp_create()
+ * @is_udp - 1 for UDP, 0 for TCP
+ * @host_addr - host address to listen on (e.g. "0.0.0.0")
+ * @host_port - host port number
+ * @guest_addr - guest address (e.g. "10.0.2.15")
+ * @guest_port - guest port number
+ * @returns 0 on success, -1 on failure
+ */
+int lkl_netdev_slirp_add_hostfwd(struct lkl_netdev *nd, int is_udp,
+				  const char *host_addr, int host_port,
+				  const char *guest_addr, int guest_port);
+
+/**
+ * lkl_netdev_slirp_remove_hostfwd - remove a port forwarding rule
+ *
+ * @nd - netdev returned by lkl_netdev_slirp_create()
+ * @is_udp - 1 for UDP, 0 for TCP
+ * @host_addr - host address
+ * @host_port - host port number
+ * @returns 0 on success, -1 on failure
+ */
+int lkl_netdev_slirp_remove_hostfwd(struct lkl_netdev *nd, int is_udp,
+				     const char *host_addr, int host_port);
+#else
+static inline struct lkl_netdev *lkl_netdev_slirp_create(void)
+{
+	return NULL;
+}
+static inline int
+lkl_netdev_slirp_add_hostfwd(struct lkl_netdev *nd, int is_udp,
+			      const char *host_addr, int host_port,
+			      const char *guest_addr, int guest_port)
+{
+	return -1;
+}
+static inline int
+lkl_netdev_slirp_remove_hostfwd(struct lkl_netdev *nd, int is_udp,
+				 const char *host_addr, int host_port)
+{
+	return -1;
+}
+#endif
+
 /**
  * lkl_add_neighbor - add a permanent arp entry
  * @ifindex - the ifindex of the interface

tools/lkl/lib/Build

@@ -1,5 +1,6 @@
 CFLAGS_posix-host.o += -D_FILE_OFFSET_BITS=64
 CFLAGS_virtio_net_vde.o += $(pkg-config --cflags vdeplug 2>/dev/null)
+CFLAGS_virtio_net_slirp.o += $(shell pkg-config --cflags slirp 2>/dev/null)
 CFLAGS_nt-host.o += -D_WIN32_WINNT=0x0600
 
 liblkl-y += fs.o
@@ -18,6 +19,7 @@ liblkl-$(LKL_HOST_CONFIG_VIRTIO_NET_FD) += virtio_net_raw.o
 liblkl-$(LKL_HOST_CONFIG_VIRTIO_NET_MACVTAP) += virtio_net_macvtap.o
 liblkl-$(LKL_HOST_CONFIG_VIRTIO_NET_DPDK) += virtio_net_dpdk.o
 liblkl-$(LKL_HOST_CONFIG_VIRTIO_NET_VDE) += virtio_net_vde.o
+liblkl-$(LKL_HOST_CONFIG_VIRTIO_NET_SLIRP) += virtio_net_slirp.o
 liblkl-$(LKL_HOST_CONFIG_VIRTIO_NET_FD) += virtio_net_pipe.o
 liblkl-$(LKL_HOST_CONFIG_NT64) += virtio_net_wintap.o
 liblkl-$(LKL_HOST_CONFIG_VFIO_PCI) += vfio_pci.o