Include /etc/hosts and /etc/resolv.conf in initramfs

Makefile

@@ -43,6 +43,8 @@ SYSCALL_TEST_WORKDIR ?= /tmp
 # NETDEV possible values are user,tap
 NETDEV ?= user
 VHOST ?= off
+# The name server listed by /etc/resolv.conf inside the Asterinas VM
+DNS_SERVER ?= none
 # End of network settings
 
 # ========================= End of Makefile options. ==========================

test/Makefile

@@ -6,6 +6,7 @@ VERBOSE ?= 1
 SYSCALL_TEST_SUITE ?= ltp
 SYSCALL_TEST_WORKDIR ?= /tmp
 ENABLE_BASIC_TEST ?= false
+DNS_SERVER ?= none
 # Set Nix's cached tarballs to be live for a longer period of time (30 days) to avoid network traffics.
 # Nix's default value is rather small (1 hour or 3600 seconds).
 NIXPKGS_CACHE_TTL := 2592000 # In seconds
@@ -65,6 +66,7 @@ $(INITRAMFS_IMAGE): $(INITRAMFS)
 		--arg enableSyscallTest $(ENABLE_SYSCALL_TEST) \
 		--argstr syscallTestSuite $(SYSCALL_TEST_SUITE) \
 		--argstr syscallTestWorkDir $(SYSCALL_TEST_WORKDIR) \
+		--argstr dnsServer ${DNS_SERVER} \
 		--arg initramfsCompressed $(INITRAMFS_COMPRESSED) \
 		--arg smp $(SMP) \
 		--out-link $@ \
@@ -80,6 +82,7 @@ $(INITRAMFS):
 		--arg enableSyscallTest $(ENABLE_SYSCALL_TEST) \
 		--argstr syscallTestSuite $(SYSCALL_TEST_SUITE) \
 		--argstr syscallTestWorkDir $(SYSCALL_TEST_WORKDIR) \
+		--argstr dnsServer ${DNS_SERVER} \
 		--arg smp $(SMP) \
 		--out-link $@ \
 		nix -A initramfs

test/nix/default.nix

@@ -1,6 +1,7 @@
 { target ? "x86_64", enableBasicTest ? false, enableBenchmark ? false
 , enableSyscallTest ? false, syscallTestSuite ? "ltp"
-, syscallTestWorkDir ? "/tmp", smp ? 1, initramfsCompressed ? true, }:
+, syscallTestWorkDir ? "/tmp", dnsServer ? "none", smp ? 1
+, initramfsCompressed ? true, }:
 let
   crossSystem.config = if target == "x86_64" then
     "x86_64-unknown-linux-gnu"
@@ -35,6 +36,7 @@ in rec {
     apps = if enableBasicTest then apps else null;
     benchmark = if enableBenchmark then benchmark else null;
     syscall = if enableSyscallTest then syscall else null;
+    dnsServer = dnsServer;
   };
   initramfs-image = pkgs.callPackage ./initramfs-image.nix {
     inherit initramfs;

test/nix/initramfs.nix

@@ -1,5 +1,5 @@
 { lib, stdenvNoCC, fetchFromGitHub, hostPlatform, writeClosure, busybox, apps
-, benchmark, syscall, }:
+, benchmark, syscall, dnsServer, pkgs }:
 let
   etc = lib.fileset.toSource {
     root = ./../src/etc;
@@ -9,7 +9,9 @@ let
     name = "gvisor-libs";
     path = "/lib/x86_64-linux-gnu";
   };
-  all_pkgs = [ busybox etc ] ++ lib.optionals (apps != null) [ apps.package ]
+  resolv_conf = pkgs.callPackage ./resolv_conf.nix { dnsServer = dnsServer; };
+  all_pkgs = [ busybox etc resolv_conf ]
+    ++ lib.optionals (apps != null) [ apps.package ]
     ++ lib.optionals (benchmark != null) [ benchmark.package ]
     ++ lib.optionals (syscall != null) [ syscall.package ];
 in stdenvNoCC.mkDerivation {
@@ -26,6 +28,8 @@ in stdenvNoCC.mkDerivation {
 
     cp -r ${etc}/* $out/etc/
 
+    cp ${resolv_conf}/resolv.conf $out/etc/
+
     ${lib.optionalString (apps != null) ''
       cp -r ${apps.package}/* $out/test/
     ''}

test/nix/resolv_conf.nix

@@ -0,0 +1,38 @@
+{ stdenv, dnsServer }:
+let
+  host_resolv_conf = builtins.path {
+    name = "host-resolv-conf";
+    path = "/etc/resolv.conf";
+  };
+in stdenv.mkDerivation {
+  name = "resolv-conf";
+  buildCommand = ''
+    RESOLV_CONF_FILE="$out/resolv.conf"
+    mkdir -p $out
+
+    is_host_resolve_conf_valid() {
+      if [ ! -f "${host_resolv_conf}" ]; then
+        return 1
+      fi
+
+      if grep -qE "nameserver\s+127\.0\.0\." "${host_resolv_conf}"; then
+        return 1
+      else
+        return 0
+      fi
+    }
+
+    if [ -n "${dnsServer}" ] && [ "${dnsServer}" != "none" ]; then
+      echo "nameserver ${dnsServer}" > "$RESOLV_CONF_FILE"
+    elif is_host_resolve_conf_valid; then
+      cp ${host_resolv_conf} $RESOLV_CONF_FILE
+      echo "resolv.conf is generated from the host's /etc/resolv.conf"
+    else
+      echo "Warning: the host's /etc/resolv.conf is not valid for the guest VM (containing lookback addresses)." >&2
+      echo "Fall back to Cloudflare's public DNS servers (1.1.1.1)." >&2
+      echo "Consider using the DNS_SERVER Makefile variable to specify DNS server explicitly." >&2
+      echo "For example: make DNS_SERVER=\"192.168.1.1\"" >&2
+      echo "nameserver 1.1.1.1" > "$RESOLV_CONF_FILE"
+    fi
+  '';
+}

test/src/etc/hosts

@@ -0,0 +1 @@
+127.0.0.1   localhost