Add "info connections" command, "info inferiors" connection number/string

This commit extends the CLI a bit for multi-target, in three ways.

#1 - New "info connections" command.

This is a new command that lists the open connections (process_stratum
targets).  For example, if you're debugging two remote connections, a
couple local/native processes, and a core dump, all at the same time,
you might see something like this:

 (gdb) info connections
   Num  What                     Description
   1    remote 192.168.0.1:9999  Remote serial target in gdb-specific protocol
   2    remote 192.168.0.2:9998  Remote serial target in gdb-specific protocol
 * 3    native                   Native process
   4    core                     Local core dump file

#2 - New "info inferiors" "Connection" column

You'll also see a new matching "Connection" column in "info
inferiors", showing you which connection an inferior is bound to:

 (gdb) info inferiors
   Num  Description       Connection                   Executable
   1    process 18526     1 (remote 192.168.0.1:9999)  target:/tmp/a.out
   2    process 18531     2 (remote 192.168.0.2:9998)  target:/tmp/a.out
   3    process 19115     3 (native)                   /tmp/prog1
   4    process 6286      4 (core)                     myprogram
 * 5    process 19122     3 (native)                   /bin/hello

#3 - Makes "add-inferior" show the inferior's target connection

"add-inferior" now shows you the connection you've just bound the
inferior to, which is the current process_stratum target:

 (gdb) add-inferior
 [New inferior 2]
 Added inferior 2 on connection 1 (extended-remote localhost:2346)

gdb/ChangeLog:
2020-01-10  Pedro Alves  <palves@redhat.com>

	* Makefile.in (COMMON_SFILES): Add target-connection.c.
	* inferior.c (uiout_field_connection): New function.
	(print_inferior): Add new "connection-id" column.
	(add_inferior_command): Show connection number/string of added
	inferior.
	* process-stratum-target.h
	(process_stratum_target::connection_string): New virtual method.
	(process_stratum_target::connection_number): New field.
	* remote.c (remote_target::connection_string): New override.
	* target-connection.c: New file.
	* target-connection.h: New file.
	* target.c (decref_target): Remove process_stratum targets from
	the connection list.
	(target_stack::push): Add process_stratum targets to the
	connection list.

gdb/testsuite/ChangeLog:
2020-01-10  Pedro Alves  <palves@redhat.com>

	* gdb.base/kill-detach-inferiors-cmd.exp: Adjust expected output
	of "add-inferior".
	* gdb.base/quit-live.exp: Likewise.
	* gdb.base/remote-exec-file.exp: Likewise.
	* gdb.guile/scm-progspace.exp: Likewise.
	* gdb.linespec/linespec.exp: Likewise.
	* gdb.mi/new-ui-mi-sync.exp: Likewise.
	* gdb.mi/user-selected-context-sync.exp: Likewise.
	* gdb.multi/multi-target.exp (setup): Add "info connection" and
	"info inferiors" tests.
	* gdb.multi/remove-inferiors.exp: Adjust expected output of
	"add-inferior".
	* gdb.multi/watchpoint-multi.exp: Likewise.
	* gdb.python/py-inferior.exp: Likewise.
	* gdb.server/extended-remote-restart.exp: Likewise.
	* gdb.threads/fork-plus-threads.exp: Adjust expected output of
	"info inferiors".
	* gdb.threads/forking-threads-plus-breakpoint.exp: Likewise.
	* gdb.trace/report.exp: Likewise.

1 files changed, 162 insertions, 0 deletions

diff --git a/gdb/target-connection.c b/gdb/target-connection.c
new file mode 100644
index 0000000..35c786b
--- /dev/null
+++ b/gdb/target-connection.c
@@ -0,0 +1,162 @@
+/* List of target connections for GDB.
+
+   Copyright (C) 2017-2020 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include "defs.h"
+#include "target-connection.h"
+
+#include <map>
+
+#include "inferior.h"
+#include "target.h"
+
+/* A map between connection number and representative process_stratum
+   target.  */
+static std::map<int, process_stratum_target *> process_targets;
+
+/* The highest connection number ever given to a target.  */
+static int highest_target_connection_num;
+
+/* See target-connection.h.  */
+
+void
+connection_list_add (process_stratum_target *t)
+{
+  if (t->connection_number == 0)
+    {
+      t->connection_number = ++highest_target_connection_num;
+      process_targets[t->connection_number] = t;
+    }
+}
+
+/* See target-connection.h.  */
+
+void
+connection_list_remove (process_stratum_target *t)
+{
+  process_targets.erase (t->connection_number);
+  t->connection_number = 0;
+}
+
+/* Make a target connection string for T.  This is usually T's
+   shortname, but it includes the result of
+   process_stratum_target::connection_string() too if T supports
+   it.  */
+
+static std::string
+make_target_connection_string (process_stratum_target *t)
+{
+  if (t->connection_string () != NULL)
+    return string_printf ("%s %s", t->shortname (),
+			  t->connection_string ());
+  else
+    return t->shortname ();
+}
+
+/* Prints the list of target connections and their details on UIOUT.
+
+   If REQUESTED_CONNECTIONS is not NULL, it's a list of GDB ids of the
+   target connections that should be printed.  Otherwise, all target
+   connections are printed.  */
+
+static void
+print_connection (struct ui_out *uiout, const char *requested_connections)
+{
+  int count = 0;
+  size_t what_len = 0;
+
+  /* Compute number of lines we will print.  */
+  for (const auto &it : process_targets)
+    {
+      if (!number_is_in_list (requested_connections, it.first))
+	continue;
+
+      ++count;
+
+      process_stratum_target *t = it.second;
+
+      size_t l = strlen (t->shortname ());
+      if (t->connection_string () != NULL)
+	l += 1 + strlen (t->connection_string ());
+
+      if (l > what_len)
+	what_len = l;
+    }
+
+  if (count == 0)
+    {
+      uiout->message (_("No connections.\n"));
+      return;
+    }
+
+  ui_out_emit_table table_emitter (uiout, 4, process_targets.size (),
+				   "connections");
+
+  uiout->table_header (1, ui_left, "current", "");
+  uiout->table_header (4, ui_left, "number", "Num");
+  /* The text in the "what" column may include spaces.  Add one extra
+     space to visually separate the What and Description columns a
+     little better.  Compare:
+      "* 1    remote :9999 Remote serial target in gdb-specific protocol"
+      "* 1    remote :9999  Remote serial target in gdb-specific protocol"
+  */
+  uiout->table_header (what_len + 1, ui_left, "what", "What");
+  uiout->table_header (17, ui_left, "description", "Description");
+
+  uiout->table_body ();
+
+  for (const auto &it : process_targets)
+    {
+      process_stratum_target *t = it.second;
+
+      if (!number_is_in_list (requested_connections, t->connection_number))
+	continue;
+
+      ui_out_emit_tuple tuple_emitter (uiout, NULL);
+
+      if (current_inferior ()->process_target () == t)
+	uiout->field_string ("current", "*");
+      else
+	uiout->field_skip ("current");
+
+      uiout->field_signed ("number", t->connection_number);
+
+      uiout->field_string ("what", make_target_connection_string (t).c_str ());
+
+      uiout->field_string ("description", t->longname ());
+
+      uiout->text ("\n");
+    }
+}
+
+/* The "info connections" command.  */
+
+static void
+info_connections_command (const char *args, int from_tty)
+{
+  print_connection (current_uiout, args);
+}
+
+void
+_initialize_target_connection ()
+{
+  add_info ("connections", info_connections_command,
+	    _("\
+Target connections in use.\n\
+Shows the list of target connections currently in use."));
+}