qemu: fixup basic tests, enable in passthru.tests

these may not be reliable enough to enable by default, but enabling
them as a passthru may allow us to get a feel for which platforms
have trouble with them

pkgs/applications/virtualization/qemu/default.nix

@@ -2,7 +2,7 @@
 , perl, pixman, vde2, alsa-lib, texinfo, flex
 , bison, lzo, snappy, libaio, libtasn1, gnutls, nettle, curl, ninja, meson, sigtool
 , makeWrapper, runtimeShell
-, attr, libcap, libcap_ng
+, attr, libcap, libcap_ng, socat
 , CoreServices, Cocoa, Hypervisor, rez, setfile
 , numaSupport ? stdenv.isLinux && !stdenv.isAarch32, numactl
 , seccompSupport ? stdenv.isLinux, libseccomp
@@ -31,6 +31,8 @@
                           ++ ["${stdenv.hostPlatform.qemuArch}-softmmu"])
                     else null)
 , nixosTestRunner ? false
+, doCheck ? false
+, qemu  # for passthru.tests
 }:
 
 let
@@ -217,7 +219,6 @@ stdenv.mkDerivation rec {
     ++ lib.optional smbdSupport "--smbd=${samba}/bin/smbd"
     ++ lib.optional uringSupport "--enable-linux-io-uring";
 
-  doCheck = false; # tries to access /dev
   dontWrapGApps = true;
 
   # QEMU attaches entitlements with codesign and strip removes those,
@@ -241,6 +242,40 @@ stdenv.mkDerivation rec {
   '';
   preBuild = "cd build";
 
+  # tests can still timeout on slower systems
+  inherit doCheck;
+  checkInputs = [ socat ];
+  preCheck = ''
+    # time limits are a little meagre for a build machine that's
+    # potentially under load.
+    substituteInPlace ../tests/unit/meson.build \
+      --replace 'timeout: slow_tests' 'timeout: 50 * slow_tests'
+    substituteInPlace ../tests/qtest/meson.build \
+      --replace 'timeout: slow_qtests' 'timeout: 50 * slow_qtests'
+    substituteInPlace ../tests/fp/meson.build \
+      --replace 'timeout: 90)' 'timeout: 300)'
+
+    # point tests towards correct binaries
+    substituteInPlace ../tests/unit/test-qga.c \
+      --replace '/bin/echo' "$(type -P echo)"
+    substituteInPlace ../tests/unit/test-io-channel-command.c \
+      --replace '/bin/socat' "$(type -P socat)"
+
+    # combined with a long package name, some temp socket paths
+    # can end up exceeding max socket name len
+    substituteInPlace ../tests/qtest/bios-tables-test.c \
+      --replace 'qemu-test_acpi_%s_tcg_%s' '%s_%s'
+
+    # get-fsinfo attempts to access block devices, disallowed by sandbox
+    sed -i -e '/\/qga\/get-fsinfo/d' -e '/\/qga\/blacklist/d' \
+      ../tests/unit/test-qga.c
+  '' + lib.optionalString stdenv.isDarwin ''
+    # skip test that stalls on darwin, perhaps due to subtle differences
+    # in fifo behaviour
+    substituteInPlace ../tests/unit/meson.build \
+      --replace "'test-io-channel-command'" "#'test-io-channel-command'"
+  '';
+
   # Add a ‘qemu-kvm’ wrapper for compatibility/convenience.
   postInstall = ''
     ln -s $out/bin/qemu-system-${stdenv.hostPlatform.qemuArch} $out/bin/qemu-kvm
@@ -248,6 +283,9 @@ stdenv.mkDerivation rec {
 
   passthru = {
     qemu-system-i386 = "bin/qemu-system-i386";
+    tests = {
+      qemu-tests = qemu.override { doCheck = true; };
+    };
   };
 
   # Builds in ~3h with 2 cores, and ~20m with a big-parallel builder.