[PATCH 07/17] Special-case "set inferior-tty /dev/tty"

[Pedro Alves <pedro@palves.net>]

The following patches will make GDB spawn inferiors in their own
session and tty by default.  Meaning, GDB will create and manage a pty
for the inferior instead of the inferior and GDB sharing the same
terminal and GDB having to juggle terminal settings depending on
whether the inferior running or gdb showing the prompt.

For some use cases however, it will still be useful to be able to tell
GDB to spawn the inferior in the same terminal & session as GDB, like
today.

Setting the inferior tty to "/dev/tty" seems like an obvious way to
get that, as /dev/tty is a special file that represents the terminal
for the current process.  This leaves "tty" with no arguments free for
a different behavior.

This patch hardcodes "/dev/tty" in is_gdb_terminal for that reason.

gdb/ChangeLog:
yyyy-mm-dd  Pedro Alves  <pedro@palves.net>

	* inflow.c (is_gdb_terminal): Hardcode "/dev/tty".
	(new_tty): Don't create a tty if is_gdb_terminal is true.
	(new_tty_postfork): Always allocate a run_terminal.
	(create_tty_session): Don't create a session if sharing the
	terminal with GDB.

Change-Id: I4dc7958f823fa4e30c21a2c3fe4d8434a5d5ed40
---
 gdb/inflow.c | 26 +++++++++++++++++---------
 1 file changed, 17 insertions(+), 9 deletions(-)

diff --git a/gdb/inflow.c b/gdb/inflow.c
index d241540c4cd..15f29dcd08e 100644
--- a/gdb/inflow.c
+++ b/gdb/inflow.c
@@ -222,6 +222,11 @@ is_gdb_terminal (const char *tty)
   struct stat other_tty;
   int res;
 
+  /* Users can explicitly set the inferior tty to "/dev/tty" to mean
+     "the GDB terminal".  */
+  if (strcmp (tty, "/dev/tty") == 0)
+    return TRIBOOL_TRUE;
+
   res = stat (tty, &other_tty);
   if (res == -1)
     return TRIBOOL_UNKNOWN;
@@ -796,9 +801,10 @@ check_syscall (const char *msg, int result)
 #endif
 
 void
-new_tty (void)
+new_tty ()
 {
-  if (inferior_thisrun_terminal == 0)
+  if (inferior_thisrun_terminal == nullptr
+      || is_gdb_terminal (inferior_thisrun_terminal))
     return;
 #if !defined(__GO32__) && !defined(_WIN32)
   int tty;
@@ -862,13 +868,13 @@ new_tty_postfork (void)
   /* Save the name for later, for determining whether we and the child
      are sharing a tty.  */
 
-  if (inferior_thisrun_terminal)
-    {
-      struct inferior *inf = current_inferior ();
-      struct terminal_info *tinfo = get_inflow_inferior_data (inf);
+  struct inferior *inf = current_inferior ();
+  struct terminal_info *tinfo = get_inflow_inferior_data (inf);
 
-      tinfo->run_terminal = xstrdup (inferior_thisrun_terminal);
-    }
+  if (inferior_thisrun_terminal != nullptr)
+    tinfo->run_terminal = xstrdup (inferior_thisrun_terminal);
+  else
+    tinfo->run_terminal = xstrdup ("/dev/tty");
 
   inferior_thisrun_terminal = NULL;
 }
@@ -927,7 +933,9 @@ create_tty_session (void)
 #ifdef HAVE_SETSID
   pid_t ret;
 
-  if (!job_control || inferior_thisrun_terminal == 0)
+  if (!job_control
+      || inferior_thisrun_terminal == nullptr
+      || is_gdb_terminal (inferior_thisrun_terminal))
     return 0;
 
   ret = setsid ();
-- 
2.26.2