[RFC] Don't create inferior in tfile target.

[Yao Qi <yao@codesourcery.com>]

In ctf target, we don't create inferior when open ctf trace file,
however we do it in tfile target.  After read the code for a while, I
don't see any reason that we need an inferior here.  The code was
added along with the tfile support patch, and was modified once by
patch [1]

I checked out the code on the revision before patch [1] was applied
bd196e7a61b03f2ea7e5dcb0aecbd49d239d6390 and I am able to reproduce
the same internal error, However, I am wondering why do we need
inferior in tfile target.  I removed the code to create inferior in
tfile_open and remove inferior in tfile_close.  The internal error can
be fixed also.  I also checked that 'info threads' and 'info
inferiors' works properly.

I talked with Stan (he wrote tfile supported code) on this, but we were
unable to recall the reason in details on creating inferior.  I post
this patch to remove the code to create inferior in tfile target.
Comments are welcome.

[1] robustify target tfile's open code
http://sourceware.org/ml/gdb-patches/2011-05/msg00477.html

gdb:

2013-05-04  Yao Qi  <yao@codesourcery.com>

	* tracepoint.c (TFILE_PID): Remove.
	(tfile_open): Don't add thread and inferior.
	(tfile_close): Don't set 'inferior_ptid'.  Don't call
	exit_inferior_silent.
	(tfile_thread_alive): Remove.
	(init_tfile_ops): Don't set field 'to_thread_alive' of
	tfile_ops.

gdb/testsuite:

2013-05-04  Yao Qi  <yao@codesourcery.com>

	* gdb.trace/tfile.exp: Test inferior and thread.

---
 gdb/testsuite/gdb.trace/tfile.exp |    3 +++
 gdb/tracepoint.c                  |   19 -------------------
 2 files changed, 3 insertions(+), 19 deletions(-)

diff --git a/gdb/testsuite/gdb.trace/tfile.exp b/gdb/testsuite/gdb.trace/tfile.exp
index 087d207..d7381eb 100644
--- a/gdb/testsuite/gdb.trace/tfile.exp
+++ b/gdb/testsuite/gdb.trace/tfile.exp
@@ -119,6 +119,9 @@ Trace buffer has 256 bytes of 4096 bytes free \\(93% full\\).*
 Not looking at any trace frame.*" \
     "tstatus on error trace file"
 
+gdb_test "info threads" "No threads\..*"
+gdb_test "info inferiors" "\\* 1    <null>\[ \t\]+${binfile}.*"
+
 # Make sure we can reopen without error.
 gdb_test \
     "interpreter-exec mi \"-target-select tfile tfile-basic.tf\"" \
diff --git a/gdb/tracepoint.c b/gdb/tracepoint.c
index 9e2c4e3..0124211 100644
--- a/gdb/tracepoint.c
+++ b/gdb/tracepoint.c
@@ -81,8 +81,6 @@
    large.  (400 - 31)/2 == 184 */
 #define MAX_AGENT_EXPR_LEN	184
 
-#define TFILE_PID (1)
-
 /* A hook used to notify the UI of tracepoint operations.  */
 
 void (*deprecated_trace_find_hook) (char *arg, int from_tty);
@@ -4273,10 +4271,6 @@ tfile_open (char *filename, int from_tty)
       throw_exception (ex);
     }
 
-  inferior_appeared (current_inferior (), TFILE_PID);
-  inferior_ptid = pid_to_ptid (TFILE_PID);
-  add_thread_silent (inferior_ptid);
-
   if (ts->traceframe_count <= 0)
     warning (_("No traceframes present in this file."));
 
@@ -4287,8 +4281,6 @@ tfile_open (char *filename, int from_tty)
   merge_uploaded_trace_state_variables (&uploaded_tsvs);
 
   merge_uploaded_tracepoints (&uploaded_tps);
-
-  post_create_inferior (&tfile_ops, from_tty);
 }
 
 /* Interpret the given line from the definitions part of the trace
@@ -4661,10 +4653,6 @@ tfile_close (void)
   if (trace_fd < 0)
     return;
 
-  pid = ptid_get_pid (inferior_ptid);
-  inferior_ptid = null_ptid;	/* Avoid confusion from thread stuff.  */
-  exit_inferior_silent (pid);
-
   close (trace_fd);
   trace_fd = -1;
   xfree (trace_filename);
@@ -5111,12 +5099,6 @@ tfile_has_registers (struct target_ops *ops)
   return traceframe_number != -1;
 }
 
-static int
-tfile_thread_alive (struct target_ops *ops, ptid_t ptid)
-{
-  return 1;
-}
-
 /* Callback for traceframe_walk_blocks.  Builds a traceframe_info
    object for the tfile target's current traceframe.  */
 
@@ -5196,7 +5178,6 @@ init_tfile_ops (void)
   tfile_ops.to_has_stack = tfile_has_stack;
   tfile_ops.to_has_registers = tfile_has_registers;
   tfile_ops.to_traceframe_info = tfile_traceframe_info;
-  tfile_ops.to_thread_alive = tfile_thread_alive;
   tfile_ops.to_magic = OPS_MAGIC;
 }
 
-- 
1.7.7.6