stored: always initialize struct mtop

When running in valgrind the ioctl() call that consumes struct mtop is
flagged as accessing uninitialized memory. This patch initializes every
struct mtop.

(cherry picked from commit 53e6700)

core/src/stored/backends/generic_tape_device.cc

@@ -48,7 +48,7 @@ void generic_tape_device::OpenDevice(DeviceControlRecord* dcr, int omode)
   file_size = 0;
   int timeout = max_open_wait;
 #if !defined(HAVE_WIN32)
-  struct mtop mt_com;
+  struct mtop mt_com{};
   utime_t start_time = time(NULL);
 #endif
 
@@ -153,7 +153,7 @@ void generic_tape_device::OpenDevice(DeviceControlRecord* dcr, int omode)
  */
 bool generic_tape_device::eod(DeviceControlRecord* dcr)
 {
-  struct mtop mt_com;
+  struct mtop mt_com{};
   bool ok = true;
   int32_t os_file;
 
@@ -328,7 +328,7 @@ void generic_tape_device::SetAteot()
  */
 bool generic_tape_device::offline()
 {
-  struct mtop mt_com;
+  struct mtop mt_com{};
 
   /*
    * Remove EOF/EOT flags.
@@ -366,7 +366,7 @@ bool generic_tape_device::offline()
  */
 bool generic_tape_device::weof(int num)
 {
-  struct mtop mt_com;
+  struct mtop mt_com{};
   int status;
   Dmsg1(129, "=== weof_dev=%s\n", prt_name);
 
@@ -415,7 +415,7 @@ bool generic_tape_device::weof(int num)
 bool generic_tape_device::fsf(int num)
 {
   int32_t os_file = 0;
-  struct mtop mt_com;
+  struct mtop mt_com{};
   int status = 0;
 
   if (!IsOpen()) {
@@ -598,7 +598,7 @@ bool generic_tape_device::fsf(int num)
  */
 bool generic_tape_device::bsf(int num)
 {
-  struct mtop mt_com;
+  struct mtop mt_com{};
   int status;
 
   if (!IsOpen()) {
@@ -645,7 +645,7 @@ static inline bool DevGetOsPos(Device* dev, struct mtget* mt_stat)
  */
 bool generic_tape_device::fsr(int num)
 {
-  struct mtop mt_com;
+  struct mtop mt_com{};
   int status;
 
   if (!IsOpen()) {
@@ -701,7 +701,7 @@ bool generic_tape_device::fsr(int num)
  */
 bool generic_tape_device::bsr(int num)
 {
-  struct mtop mt_com;
+  struct mtop mt_com{};
   int status;
 
   if (!IsOpen()) {
@@ -744,7 +744,7 @@ bool generic_tape_device::bsr(int num)
 bool generic_tape_device::LoadDev()
 {
 #ifdef MTLOAD
-  struct mtop mt_com;
+  struct mtop mt_com{};
 #endif
 
   if (fd_ < 0) {
@@ -782,7 +782,7 @@ bool generic_tape_device::LoadDev()
 void generic_tape_device::LockDoor()
 {
 #ifdef MTLOCK
-  struct mtop mt_com;
+  struct mtop mt_com{};
 
   mt_com.mt_op = MTLOCK;
   mt_com.mt_count = 1;
@@ -793,7 +793,7 @@ void generic_tape_device::LockDoor()
 void generic_tape_device::UnlockDoor()
 {
 #ifdef MTUNLOCK
-  struct mtop mt_com;
+  struct mtop mt_com{};
 
   mt_com.mt_op = MTUNLOCK;
   mt_com.mt_count = 1;
@@ -834,7 +834,7 @@ static inline void OsClrerror(Device* dev)
  */
 static inline void OsClrerror(Device* dev)
 {
-  struct mtop mt_com;
+  struct mtop mt_com{};
 
   /*
    * Clear any error condition on the tape
@@ -991,7 +991,7 @@ void generic_tape_device::SetOsDeviceParameters(DeviceControlRecord* dcr)
   }
 
 #if defined(HAVE_LINUX_OS) || defined(HAVE_WIN32)
-  struct mtop mt_com;
+  struct mtop mt_com{};
 
   Dmsg0(100, "In SetOsDeviceParameters\n");
 #if defined(MTSETBLK)
@@ -1021,7 +1021,7 @@ void generic_tape_device::SetOsDeviceParameters(DeviceControlRecord* dcr)
 #endif
 
 #ifdef HAVE_NETBSD_OS
-  struct mtop mt_com;
+  struct mtop mt_com{};
   if (dev->min_block_size == dev->max_block_size &&
       dev->min_block_size == 0) { /* variable block mode */
     mt_com.mt_op = MTSETBSIZ;
@@ -1040,7 +1040,7 @@ void generic_tape_device::SetOsDeviceParameters(DeviceControlRecord* dcr)
 #endif
 
 #if HAVE_FREEBSD_OS || HAVE_OPENBSD_OS
-  struct mtop mt_com;
+  struct mtop mt_com{};
   if (dev->min_block_size == dev->max_block_size &&
       dev->min_block_size == 0) { /* variable block mode */
     mt_com.mt_op = MTSETBSIZ;
@@ -1068,7 +1068,7 @@ void generic_tape_device::SetOsDeviceParameters(DeviceControlRecord* dcr)
 #endif
 
 #ifdef HAVE_SUN_OS
-  struct mtop mt_com;
+  struct mtop mt_com{};
   if (dev->min_block_size == dev->max_block_size &&
       dev->min_block_size == 0) { /* variable block mode */
     mt_com.mt_op = MTSRSZ;
@@ -1103,7 +1103,7 @@ int32_t generic_tape_device::GetOsTapeFile()
  */
 bool generic_tape_device::rewind(DeviceControlRecord* dcr)
 {
-  struct mtop mt_com;
+  struct mtop mt_com{};
   unsigned int i;
   bool first = true;