Make error messages a bit more user friendly.

Updated error messages so that it doesn't print full Go struct representations
when running a new container in a sandbox. For example, this occurs frequently
when commands are not found when doing a 'kubectl exec'.

PiperOrigin-RevId: 219729141
Change-Id: Ic3a7bc84cd7b2167f495d48a1da241d621d3ca09

pkg/sentry/control/proc.go

@@ -19,6 +19,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"sort"
+	"strings"
 	"text/tabwriter"
 	"time"
 
@@ -88,6 +89,16 @@ type ExecArgs struct {
 	ContainerID string
 }
 
+// String prints the arguments as a string.
+func (args ExecArgs) String() string {
+	a := make([]string, len(args.Argv))
+	copy(a, args.Argv)
+	if args.Filename != "" {
+		a[0] = args.Filename
+	}
+	return strings.Join(a, " ")
+}
+
 // Exec runs a new task.
 func (proc *Proc) Exec(args *ExecArgs, waitStatus *uint32) error {
 	newTG, _, _, err := proc.execAsync(args)

runsc/boot/loader.go

@@ -618,7 +618,7 @@ func (l *Loader) executeAsync(args *control.ExecArgs) (kernel.ThreadID, error) {
 	ep, ok := l.processes[rootKey]
 	l.mu.Unlock()
 	if !ok {
-		return 0, fmt.Errorf("cannot exec in container %q: no such container", args.ContainerID)
+		return 0, fmt.Errorf("no such container: %q", args.ContainerID)
 	}
 	ep.tg.Leader().WithMuLocked(func(t *kernel.Task) {
 		args.Root = t.FSContext().RootDirectory()
@@ -631,7 +631,7 @@ func (l *Loader) executeAsync(args *control.ExecArgs) (kernel.ThreadID, error) {
 	proc := control.Proc{Kernel: l.k}
 	tg, tgid, ttyFile, err := control.ExecAsync(&proc, args)
 	if err != nil {
-		return 0, fmt.Errorf("error executing: %+v: %v", args, err)
+		return 0, err
 	}
 
 	// Insert the process into processes so that we can wait on it

runsc/sandbox/sandbox.go

@@ -229,7 +229,7 @@ func (s *Sandbox) Execute(args *control.ExecArgs) (int32, error) {
 	// Send a message to the sandbox control server to start the container.
 	var pid int32
 	if err := conn.Call(boot.ContainerExecuteAsync, args, &pid); err != nil {
-		return 0, fmt.Errorf("error executing in sandbox: %v", err)
+		return 0, fmt.Errorf("error executing command %q in sandbox: %v", args, err)
 	}
 	return pid, nil
 }