cmd/runqemubuildlet: run as root on darwin

QEMU needs to run as root on darwin for working networking. Currently we
run runqemubuildlet as a normal user, and invoke QEMU with `sudo`.
Unfortunately, this means that runqemubuildlet doesn't have permission
to signal QEMU when the health check fails.

Instead, run runqemubuildlet as root so it has permission to signal
QEMU.

For golang/go#48945.

Change-Id: I07bd61168462c7272db05c328eb11dcd39743f79
Reviewed-on: https://go-review.googlesource.com/c/build/+/456042
Reviewed-by: Heschi Kreinick <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Michael Pratt <[email protected]>

Author: prattmic

cmd/runqemubuildlet/darwin.go

@@ -43,13 +43,11 @@ func darwinCmd(base string) *exec.Cmd {
 
 	disk := filepath.Join(base, "macos.qcow2")
 
-	// vmnet-shared requires that we run QEMU as root.
+	// Note that vmnet-shared requires that we run QEMU as root, so
+	// runqemubuildlet must run as root.
 	//
 	// These arguments should be kept in sync with env/darwin/aws/qemu.sh.
 	args := []string{
-		"env",
-		fmt.Sprintf("DYLD_LIBRARY_PATH=%s", filepath.Join(sysroot, "lib")),
-		filepath.Join(sysroot, "bin/qemu-system-x86_64"),
 		// Discard disk changes on exit.
 		"-snapshot",
 		"-m", "4096",
@@ -86,6 +84,9 @@ func darwinCmd(base string) *exec.Cmd {
 		args = append(args, "-device", fmt.Sprintf("vmxnet3,netdev=net0,id=net0,mac=52:54:00:c9:18:0%d", *guestIndex))
 	}
 
-	cmd := exec.Command("sudo", args...)
+	cmd := exec.Command(filepath.Join(sysroot, "bin/qemu-system-x86_64"), args...)
+	cmd.Env = append(os.Environ(),
+		fmt.Sprintf("DYLD_LIBRARY_PATH=%s", filepath.Join(sysroot, "lib")),
+	)
 	return cmd
 }

cmd/runqemubuildlet/main.go

@@ -56,7 +56,7 @@ func main() {
 		}
 
 		if err := runGuest(ctx, cmd); err != nil {
-			log.Printf("runWindows10() = %v. Retrying in 10 seconds.", err)
+			log.Printf("runGuest() = %v. Retrying in 10 seconds.", err)
 			time.Sleep(10 * time.Second)
 			continue
 		}

env/darwin/aws/README.md

@@ -153,7 +153,7 @@ builders.
 
 while true; do
   echo "Running QEMU..."
-  $HOME/runqemubuildlet -guest-os=darwin -macos-version=${MACOS_VERSION?} -osk=${OSK_VALUE?} -guest-index=1 -buildlet-healthz-url="http://192.168.64.101:8080/healthz"
+  sudo $HOME/runqemubuildlet -guest-os=darwin -macos-version=${MACOS_VERSION?} -osk=${OSK_VALUE?} -guest-index=1 -buildlet-healthz-url="http://192.168.64.101:8080/healthz"
 done
 ```
 
@@ -164,7 +164,7 @@ done
 
 while true; do
   echo "Running QEMU..."
-  $HOME/runqemubuildlet -guest-os=darwin -macos-version=${MACOS_VERSION?} -osk=${OSK_VALUE?} -guest-index=2 -buildlet-healthz-url="http://192.168.64.102:8080/healthz"
+  sudo $HOME/runqemubuildlet -guest-os=darwin -macos-version=${MACOS_VERSION?} -osk=${OSK_VALUE?} -guest-index=2 -buildlet-healthz-url="http://192.168.64.102:8080/healthz"
 done
 ```