vm/qemu: improve debug output

* vm/qemu: Improve debug output.

When running in debug mode, the number of VMs is reduced to 1.
State this in the debug output.

* vm/qemu: Don't start debug output with a capital letter.

As requested by Dimitry.

* vm: Provide debug message when reduing number of VMs.

Apply this change to all affected platforms for consistency.
Suggested by Dmitry.

* Add myself to AUTHORS/CONTRIBUTORS files.

* vm: Fix compilation issues missed in earlier commit.

* vm: Use logging to write debug message.

AUTHORS

@@ -27,3 +27,4 @@ Chi Pham
 Anton Lindqvist
 Greg Steuck
 Shankara Pailoor
+Michael Tuexen

CONTRIBUTORS

@@ -38,3 +38,4 @@ Joey Jiao
 Anton Lindqvist
 Tobin Harding
 Shankara Pailoor
+Michael Tuexen

vm/gce/gce.go

@@ -74,7 +74,8 @@ func ctor(env *vmimpl.Env) (vmimpl.Pool, error) {
 	if cfg.Count < 1 || cfg.Count > 1000 {
 		return nil, fmt.Errorf("invalid config param count: %v, want [1, 1000]", cfg.Count)
 	}
-	if env.Debug {
+	if env.Debug && cfg.Count > 1 {
+		log.Logf(0, "limiting number of VMs from %v to 1 in debug mode", cfg.Count)
 		cfg.Count = 1
 	}
 	if cfg.MachineType == "" {

vm/gvisor/gvisor.go

@@ -18,6 +18,7 @@ import (
 	"time"
 
 	"github.com/google/syzkaller/pkg/config"
+	"github.com/google/syzkaller/pkg/log"
 	"github.com/google/syzkaller/pkg/osutil"
 	"github.com/google/syzkaller/vm/vmimpl"
 )
@@ -58,7 +59,8 @@ func ctor(env *vmimpl.Env) (vmimpl.Pool, error) {
 	if cfg.Count < 1 || cfg.Count > 128 {
 		return nil, fmt.Errorf("invalid config param count: %v, want [1, 128]", cfg.Count)
 	}
-	if env.Debug {
+	if env.Debug && cfg.Count > 1 {
+		log.Logf(0, "limiting number of VMs from %v to 1 in debug mode", cfg.Count)
 		cfg.Count = 1
 	}
 	if !osutil.IsExist(env.Image) {

vm/isolated/isolated.go

@@ -62,7 +62,8 @@ func ctor(env *vmimpl.Env) (vmimpl.Pool, error) {
 			return nil, fmt.Errorf("bad target %q: %v", target, err)
 		}
 	}
-	if env.Debug {
+	if env.Debug && len(cfg.Targets) > 1 {
+		log.Logf(0, "limiting number of targets from %v to 1 in debug mode", len(cfg.Targets))
 		cfg.Targets = cfg.Targets[:1]
 	}
 	pool := &Pool{

vm/kvm/kvm.go

@@ -16,6 +16,7 @@ import (
 	"time"
 
 	"github.com/google/syzkaller/pkg/config"
+	"github.com/google/syzkaller/pkg/log"
 	"github.com/google/syzkaller/pkg/osutil"
 	"github.com/google/syzkaller/vm/vmimpl"
 )
@@ -67,7 +68,8 @@ func ctor(env *vmimpl.Env) (vmimpl.Pool, error) {
 	if cfg.Count < 1 || cfg.Count > 128 {
 		return nil, fmt.Errorf("invalid config param count: %v, want [1, 128]", cfg.Count)
 	}
-	if env.Debug {
+	if env.Debug && cfg.Count > 1 {
+		log.Logf(0, "limiting number of VMs from %v to 1 in debug mode", cfg.Count)
 		cfg.Count = 1
 	}
 	if env.Image != "" {

vm/qemu/qemu.go

@@ -180,7 +180,8 @@ func ctor(env *vmimpl.Env) (vmimpl.Pool, error) {
 	if cfg.Count < 1 || cfg.Count > 128 {
 		return nil, fmt.Errorf("invalid config param count: %v, want [1, 128]", cfg.Count)
 	}
-	if env.Debug {
+	if env.Debug && cfg.Count > 1 {
+		log.Logf(0, "limiting number of VMs from %v to 1 in debug mode", cfg.Count)
 		cfg.Count = 1
 	}
 	if _, err := exec.LookPath(cfg.Qemu); err != nil {

vm/vmm/vmm.go

@@ -69,7 +69,8 @@ func ctor(env *vmimpl.Env) (vmimpl.Pool, error) {
 	if cfg.Count < 1 || cfg.Count > 128 {
 		return nil, fmt.Errorf("invalid config param count: %v, want [1-128]", cfg.Count)
 	}
-	if env.Debug {
+	if env.Debug && cfg.Count > 1 {
+		log.Logf(0, "limiting number of VMs from %v to 1 in debug mode", cfg.Count)
 		cfg.Count = 1
 	}
 	if cfg.Mem < 128 || cfg.Mem > 1048576 {