virsh: Remember terminal state when starting and add helpers

This patch adds instrumentation to allow modification of config of the
terminal in virsh and successful reset of the state afterwards.

The added helpers allow to disable receiving of SIGINT when pressing the
key sequence (Ctrl+C usualy). This normally sends SIGINT to the
foreground process group which kills ssh processes used for transport of
the data.

tools/virsh.c

@@ -2213,6 +2213,53 @@ vshPrintExtra(vshControl *ctl, const char *format, ...)
 }
 
 
+bool
+vshTTYIsInterruptCharacter(vshControl *ctl,
+                           const char chr)
+{
+    if (ctl->istty &&
+        ctl->termattr.c_cc[VINTR] == chr)
+        return true;
+
+    return false;
+}
+
+
+int
+vshTTYDisableInterrupt(vshControl *ctl)
+{
+    struct termios termset = ctl->termattr;
+
+    if (!ctl->istty)
+        return -1;
+
+    /* check if we need to set the terminal */
+    if (termset.c_cc[VINTR] == _POSIX_VDISABLE)
+        return 0;
+
+    termset.c_cc[VINTR] = _POSIX_VDISABLE;
+    termset.c_lflag &= ~ICANON;
+
+    if (tcsetattr(STDIN_FILENO, TCSANOW, &termset) < 0)
+        return -1;
+
+    return 0;
+}
+
+
+int
+vshTTYRestore(vshControl *ctl)
+{
+    if (!ctl->istty)
+        return 0;
+
+    if (tcsetattr(STDIN_FILENO, TCSAFLUSH, &ctl->termattr) < 0)
+        return -1;
+
+    return 0;
+}
+
+
 void
 vshError(vshControl *ctl, const char *format, ...)
 {
@@ -3157,6 +3204,13 @@ main(int argc, char **argv)
         return EXIT_FAILURE;
     }
 
+    if (isatty(STDIN_FILENO)) {
+        ctl->istty = true;
+
+        if (tcgetattr(STDIN_FILENO, &ctl->termattr) < 0)
+            ctl->istty = false;
+    }
+
     if (virMutexInit(&ctl->lock) < 0) {
         vshError(ctl, "%s", _("Failed to initialize mutex"));
         return EXIT_FAILURE;

tools/virsh.h

@@ -32,6 +32,7 @@
 # include <unistd.h>
 # include <sys/stat.h>
 # include <inttypes.h>
+# include <termios.h>
 
 # include "internal.h"
 # include "virerror.h"
@@ -240,6 +241,9 @@ struct _vshControl {
 
     const char *escapeChar;     /* String representation of
                                    console escape character */
+
+    struct termios termattr;    /* settings of the tty terminal */
+    bool istty;                 /* is the terminal a tty */
 };
 
 struct _vshCmdGrp {
@@ -350,6 +354,11 @@ void vshReportError(vshControl *ctl);
 void vshResetLibvirtError(void);
 void vshSaveLibvirtError(void);
 
+/* terminal modifications */
+bool vshTTYIsInterruptCharacter(vshControl *ctl, const char chr);
+int vshTTYDisableInterrupt(vshControl *ctl);
+int vshTTYRestore(vshControl *ctl);
+
 /* allocation wrappers */
 void *_vshMalloc(vshControl *ctl, size_t sz, const char *filename, int line);
 # define vshMalloc(_ctl, _sz)    _vshMalloc(_ctl, _sz, __FILE__, __LINE__)