Backup serial options on open, restore on close

Before altering the serial port settings, make a copy of the settings
and track it by the fd. On serial port close, restore the original
settings for that port.

On Mac OS the Prolific PL2032 kernel driver locks up if closing without
first restoring the options. When this happens, further usage of the port
is impossible until computer is rebooted, which cannot even be done
without a hard power-off.
With this fix, a clean close make sure we can re-open the port again.

src/serial.c

@@ -88,6 +88,19 @@
 static int uh_ptt_fd   = -1;
 static int uh_radio_fd = -1;
 
+typedef struct term_options_backup {
+    int fd;
+#if defined(HAVE_TERMIOS_H)
+    struct termios options;
+#elif defined(HAVE_TERMIO_H)
+    struct termio options;
+#elif defined(HAVE_SGTTY_H)
+    struct sgttyb sg;
+#endif
+    struct term_options_backup *next;
+} term_options_backup_t;
+static term_options_backup_t *term_options_backup_head = NULL;
+
 
 /*
  * This function simply returns TRUE if the argument matches uh_radio_fd and
@@ -211,14 +224,15 @@ int HAMLIB_API serial_setup(hamlib_port_t *rp)
     /* There's a lib replacement for termios under Mingw */
 #if defined(HAVE_TERMIOS_H)
     speed_t speed;            /* serial comm speed */
-    struct termios options;
+    struct termios options, orig_options;
 #elif defined(HAVE_TERMIO_H)
-    struct termio options;
+    struct termio options, orig_options;
 #elif defined(HAVE_SGTTY_H)
-    struct sgttyb sg;
+    struct sgttyb sg, orig_sg;
 #else
 #  error "No term control supported!"
 #endif
+    term_options_backup_t *term_backup = NULL;
 
     rig_debug(RIG_DEBUG_VERBOSE, "%s called\n", __func__);
 
@@ -234,10 +248,13 @@ int HAMLIB_API serial_setup(hamlib_port_t *rp)
      */
 #if defined(HAVE_TERMIOS_H)
     tcgetattr(fd, &options);
+    memcpy(&orig_options, &options, sizeof(orig_options));
 #elif defined(HAVE_TERMIO_H)
     IOCTL(fd, TCGETA, &options);
+    memcpy(&orig_options, &options, sizeof(orig_options));
 #else   /* sgtty */
     IOCTL(fd, TIOCGETP, &sg);
+    memcpy(&orig_sg, &sg, sizeof(orig_sg));
 #endif
 
 #ifdef HAVE_CFMAKERAW
@@ -518,6 +535,19 @@ int HAMLIB_API serial_setup(hamlib_port_t *rp)
 
 #endif
 
+    // Store a copy of the original options for this FD, to be restored on close.
+    term_backup = malloc(sizeof(term_options_backup_t));
+    term_backup-> fd = fd;
+#if defined(HAVE_TERMIOS_H) || defined(HAVE_TERMIO_H)
+    memcpy(&term_backup->options, &orig_options, sizeof(orig_options));
+#elif defined(HAVE_SGTTY_H)
+    memcpy(&term_backup->sg, &orig_sg, sizeof(orig_sg));
+#endif
+
+    // insert at head of list
+    term_backup->next = term_options_backup_head;
+    term_options_backup_head = term_backup;
+
     return RIG_OK;
 }
 
@@ -597,6 +627,7 @@ int ser_open(hamlib_port_t *p)
 int ser_close(hamlib_port_t *p)
 {
     int rc;
+    term_options_backup_t *term_backup, *term_backup_prev;
 
     rig_debug(RIG_DEBUG_VERBOSE, "%s called\n", __func__);
 
@@ -619,6 +650,63 @@ int ser_close(hamlib_port_t *p)
         return 0;
     }
 
+    // Find backup termios options to restore before closing
+    term_backup = term_options_backup_head;
+    term_backup_prev = term_options_backup_head;
+    while(term_backup) {
+        if(term_backup->fd == p->fd) {
+            // Found matching. Remove from list
+            if(term_backup == term_options_backup_head) {
+                term_options_backup_head = term_backup->next;
+            } else {
+                term_backup_prev->next = term_backup->next;
+            }
+            break;
+        }
+        term_backup_prev = term_backup;
+        term_backup = term_backup->next;
+    }
+
+    // Restore backup termios
+    if(term_backup) {
+        rig_debug(RIG_DEBUG_VERBOSE, "%s: restoring options\n", __func__);
+#if defined(HAVE_TERMIOS_H)
+
+        if (tcsetattr(p->fd, TCSANOW, &term_backup->options) == -1)
+        {
+            rig_debug(RIG_DEBUG_ERR,
+                     "%s: tcsetattr restore failed: %s\n",
+                     __func__,
+                     strerror(errno));
+        }
+
+#elif defined(HAVE_TERMIO_H)
+
+        if (IOCTL(p->fd, TCSETA, &term_backup->options) == -1)
+        {
+            rig_debug(RIG_DEBUG_ERR,
+                     "%s: ioctl(TCSETA) restore failed: %s\n",
+                     __func__,
+                     strerror(errno));
+        }
+
+#else
+
+        /* sgtty */
+        if (IOCTL(p->fd, TIOCSETP, &term_backup->sg) == -1)
+        {
+            rig_debug(RIG_DEBUG_ERR,
+                     "%s: ioctl(TIOCSETP) restore failed: %s\n",
+                     __func__,
+                     strerror(errno));
+        }
+#endif
+
+        free(term_backup);
+    } else {
+        rig_debug(RIG_DEBUG_WARN, "%s: no options for fd to restore\n", __func__);
+    }
+
     rc = CLOSE(p->fd);
     p->fd = -1;
     return rc;