Re: [patch] Change trace buffer size(v4)

["Abid, Hafiz" <hafiz_abid@mentor.com>]

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Hi Pedro,
Thanks for review. Here is an updated patch.

On 04/03/13 20:43:20, Pedro Alves wrote:
> One idea to make the testsuite check this would be to leverage  
> "tstatus",
> which prints the trace buffer size:
Done.

> The minus sign was missing:
> if (val < 0)
>     {
>       *buf++ = '-';
>       buf += hexnumstr (buf, (ULONGEST) -val);
>     }​
>   else
>     buf += hexnumstr (buf, (ULONGEST) val);
Done.

> Thanks.  The qSupported feature need to be documented as well.
Done.

> Dunno, haven't looked in detail but I'm hoping it to
> be obvious to whoever debugs it.  ;-)
I will look into it.

> 
> s/Added/Add/
Fixed. Sorry for making this mistake twice.

> Use '.', not ',' to separate changes.  "add realloc option" doesn't
> really make sense.  I can guess it referred to the "if" in a previous
> revision?
Fixed.

> s/Added/Add/
Fixed.

> 
> >     (Tracepoint Packets): Document QTBuffer:size .
> Spurious space after that last '.'.
Fixed.

> 
> This new feature needs to be documented as well.
Done.

> 
> -  /* There currently no way to change the buffer size.  */
> -  const int sizeOfBuffer = 5 * 1024 * 1024;
> 
> Not sure if that was intended.  If it was, please do that
> as a separate change.
Changed it back to 5*1024*1024;

> > +static LONGEST trace_buffer_size;
> Misses leading comment.
Fixed.
> > +  init_trace_buffer (sval);
> 
> Oh, I just realized this does nothing to update
> the trace buffer of the in-process agent.  :-/
Changing IPA trace buffer was not supported in this patch.
Do you think that it must be done before this patch can go in?

> > +  trace_debug ("Trace buffer is now %s bytes",
> > +	       plongest (trace_buffer_size));
> > +  write_ok (own_buf);
> 
> Might as well write the more concise:
> 
>     if (sval == trace_buffer_size)
>       {
>         init_trace_buffer (sval);
>         trace_debug ("Trace buffer is now %s bytes",
> 	       plongest (trace_buffer_size));
>       }
>     write_ok (own_buf);
I think you mean to say that there is no harm in calling  
init_trace_buffer
when sval == trace_buffer_size, as xrealloc will not do anything. So I
removed the check.

> 
> > +      if (val < 0 && val != -1)
> > +	{
> > +	  warning (_("Invalid value %s for the size of trace buffer."),
> > +		   plongest (val) );
> 
> Should really be an assertion.  There should be no way to
> trigger this, unless there's a bug elsewhere, right?
Yes. Only -1 in negative number should come here. So added an assertion.

> 
> > +      putpkt (rs->buf);
> > +      getpkt (&rs->buf, &rs->buf_size, 0);
> 
> Any reason this version lost remote_get_noisy_reply?
I noticed that packet_ok () is used with getpkt thoughout the file. So I
removed remote_get_noisy_reply.

> 
> > +      result = packet_ok (rs->buf,
> > +		  &remote_protocol_packets[PACKET_QTBuffer_size]);

> > +gdb_test "show trace-buffer-size $BUFFER_SIZE" \
> > +"Requested size of trace buffer is $BUFFER_SIZE.*" \
> > +"Show Trace Buffer Size"
> Please indent the continuation lines, like you do below.
Fixed. Sorry again on this. I should have been more careful.

> > +  "Buffer full check 1"
> s/Buffer/buffer/
Fixed.
> 
> > +
> > +# Use the default size  and trace buffer should not be
> > +# full this time.
> 
> Spurious double space after size.  I think connecting
> the independent clauses with "and" reads a bit confusingly.
> I suggest:
> 
>   # Use the default size -- the trace buffer should not end up
>   # full this time.
Fixed

> 
> > +  ".*Trace is running on the target.*" \
> > +  "Buffer full check 2"
> 
> s/Buffer/buffer/
Fixed.

> > +static int trace_buffer_size = -1;
> > +
> 
> This is used with:
> 
> extern void
>   add_setshow_zuinteger_unlimited_cmd (char *name,
> 				       enum command_class class,
> 				       unsigned int *var,
>                                        ^^^^^^^^^^^^
> 
> So, ... we were discussing this in the other thread.
> Not sure what to tell you to do here.  :-)  My inclination
> is to change the function to take a signed integer, and
> use -1 instead of UINT_MAX.
I see that Yao has already sent a patch for it. So probably I don't  
need any change
here.

Thanks,
Abid

2012-03-05  Stan Shebs  <stan@codesourcery.com>
	    Hafiz Abid Qadeer  <abidh@codesourcery.com>

	gdb/
	* NEWS: Mention set and show trace-buffer-size commands.
	Mention new packet.
	* target.h (struct target_ops): New method
	to_set_trace_buffer_size.
	(target_set_trace_buffer_size): New macro.
	* target.c (update_current_target): Set up new method.
	* tracepoint.c (trace_buffer_size): New global.
	(start_tracing): Send it to the target.
	(set_trace_buffer_size): New function.
	(_initialize_tracepoint): Add new setshow for trace-buffer-size.
	* remote.c (remote_set_trace_buffer_size): New function.
	(_initialize_remote): Use it.
	(PACKET_QTBuffer_size): New enum.
	(remote_protocol_features): Add an entry for
	PACKET_QTBuffer_size.

	gdb/gdbserver/
	* tracepoint.c (trace_buffer_size): New global.
	(DEFAULT_TRACE_BUFFER_SIZE): New define.
	(init_trace_buffer): Change to one-argument function. Allocate
	trace buffer memory.
	(handle_tracepoint_general_set): Call cmd_bigqtbuffer_size to
	handle QTBuffer:size packet.
	(cmd_bigqtbuffer_size): New function.
	(initialize_tracepoint): Call init_trace_buffer with
	DEFAULT_TRACE_BUFFER_SIZE.
	* server.c (handle_query): Add QTBuffer:size in the
	supported packets.

	gdb/doc/
	* gdb.texinfo (Starting and Stopping Trace Experiments):  
Document
	trace-buffer-size set and show commands.
	(Tracepoint Packets): Document QTBuffer:size.
	(General Query Packets): Document QTBuffer:size.

	gdb/testsuite/
	* gdb.trace/trace-buffer-size.exp: New file.
	* gdb.trace/trace-buffer-size.c: New file.

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diff --git a/gdb/NEWS b/gdb/NEWS
index 0877aa2..3fb68eb 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -104,6 +104,10 @@ set debug notification
 show debug notification
   Control display of debugging info for async remote notification.
 
+set trace-buffer-size
+show trace-buffer-size
+  Request target to change the size of trace buffer.
+
 * Removed commands
 
   ** For the Renesas Super-H architecture, the "regs" command has been removed
@@ -159,6 +163,11 @@ show filename-display
   feature to be enabled.  For more information, see:
       http://fedoraproject.org/wiki/Features/MiniDebugInfo
 
+* New remote packets
+
+QTBuffer:size
+   Set the size of trace buffer.
+
 *** Changes in GDB 7.5
 
 * GDB now supports x32 ABI.  Visit <http://sites.google.com/site/x32abi/>
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 5f39d2e..34226ce 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -11728,6 +11728,25 @@ for instance if you are looking at frames from a trace file.
 @end table
 
 @table @code
+@item set trace-buffer-size @var{n}
+@kindex set trace-buffer-size
+Request that the target use a trace buffer of @var{n} bytes.  Not all
+targets will honor the request; they may have a compiled-in size for
+the trace buffer, or some other limitation.  Set to a value of
+@code{-1} to let the target use whatever size it likes.  This is also
+the default.
+
+@item show trace-buffer-size
+@kindex show trace-buffer-size
+Show the current requested size for the trace buffer.  Note that this
+will only match the actual size if the target supports size-setting,
+and was able to handle the requested size.  For instance, if the
+target can only change buffer size between runs, this variable will
+not reflect the change until the next run starts.  Use @code{tstatus}
+to get a report of the actual buffer size.
+@end table
+
+@table @code
 @item set trace-user @var{text}
 @kindex set trace-user
 
@@ -37373,6 +37392,11 @@ These are the currently defined stub features and their properties:
 @tab @samp{-}
 @tab No
 
+@item @samp{QTBuffer:size}
+@tab No
+@tab @samp{-}
+@tab No
+
 @item @samp{tracenz}
 @tab No
 @tab @samp{-}
@@ -37527,6 +37551,10 @@ The remote stub supports the @samp{QTEnable} (@pxref{QTEnable}) and
 @samp{QTDisable} (@pxref{QTDisable}) packets that allow tracepoints
 to be enabled and disabled while a trace experiment is running.
 
+@item QTBuffer:size
+The remote stub supports the @samp{QTBuffer:size} (@pxref{QTBuffer:size})
+packet that allows to change the size of trace buffer.
+
 @item tracenz
 @cindex string tracing, in remote protocol
 The remote stub supports the @samp{tracenz} bytecode for collecting strings.
@@ -38450,6 +38478,11 @@ available.
 This packet directs the target to use a circular trace buffer if
 @var{value} is 1, or a linear buffer if the value is 0.
 
+@item QTBuffer:size:@var{size}
+This packet directs the target to make the trace buffer be of size
+@var{size} if possible.  A value of @code{-1} tells the target to
+use whatever size it prefers.
+
 @item QTNotes:@r{[}@var{type}:@var{text}@r{]}@r{[};@var{type}:@var{text}@r{]}@dots{}
 @cindex @samp{QTNotes} packet
 This packet adds optional textual notes to the trace run.  Allowable
diff --git a/gdb/gdbserver/server.c b/gdb/gdbserver/server.c
index 768eae7..922a5bf 100644
--- a/gdb/gdbserver/server.c
+++ b/gdb/gdbserver/server.c
@@ -1637,6 +1637,7 @@ handle_query (char *own_buf, int packet_len, int *new_packet_len_p)
 	  strcat (own_buf, ";qXfer:statictrace:read+");
 	  strcat (own_buf, ";qXfer:traceframe-info:read+");
 	  strcat (own_buf, ";EnableDisableTracepoints+");
+	  strcat (own_buf, ";QTBuffer:size+");
 	  strcat (own_buf, ";tracenz+");
 	}
 
diff --git a/gdb/gdbserver/tracepoint.c b/gdb/gdbserver/tracepoint.c
index 0f83ae6..cb5ef15 100644
--- a/gdb/gdbserver/tracepoint.c
+++ b/gdb/gdbserver/tracepoint.c
@@ -30,6 +30,8 @@
 
 #include "ax.h"
 
+#define DEFAULT_TRACE_BUFFER_SIZE 5242880 /* 5*1024*1024 */
+
 /* This file is built for both GDBserver, and the in-process
    agent (IPA), a shared library that includes a tracing agent that is
    loaded by the inferior to support fast tracepoints.  Fast
@@ -992,6 +994,10 @@ int current_traceframe = -1;
 static int circular_trace_buffer;
 #endif
 
+/* Size of the trace buffer.  */
+
+static LONGEST trace_buffer_size;
+
 /* Pointer to the block of memory that traceframes all go into.  */
 
 static unsigned char *trace_buffer_lo;
@@ -1478,9 +1484,13 @@ clear_inferior_trace_buffer (void)
 #endif
 
 static void
-init_trace_buffer (unsigned char *buf, int bufsize)
+init_trace_buffer (LONGEST bufsize)
 {
-  trace_buffer_lo = buf;
+  trace_buffer_size = bufsize;
+
+  /* If we already have a trace buffer, try realloc'ing.  */
+  trace_buffer_lo = xrealloc (trace_buffer_lo, bufsize);
+
   trace_buffer_hi = trace_buffer_lo + bufsize;
 
   clear_trace_buffer ();
@@ -4020,6 +4030,37 @@ cmd_bigqtbuffer_circular (char *own_buf)
 }
 
 static void
+cmd_bigqtbuffer_size (char *own_buf)
+{
+  ULONGEST val;
+  LONGEST sval;
+  char *packet = own_buf;
+
+  /* Can't change the size during a tracing run.  */
+  if (tracing)
+    {
+      write_enn (own_buf);
+      return;
+    }
+
+  packet += strlen ("QTBuffer:size:");
+
+  /* -1 is sent as literal "-1".  */
+  if (strcmp (packet, "-1") == 0)
+    sval = DEFAULT_TRACE_BUFFER_SIZE;
+  else
+    {
+      unpack_varlen_hex (packet, &val);
+      sval = (LONGEST)val;
+    }
+ 
+  init_trace_buffer (sval);
+  trace_debug ("Trace buffer is now %s bytes",
+	       plongest (trace_buffer_size));
+  write_ok (own_buf);
+}
+
+static void
 cmd_qtnotes (char *own_buf)
 {
   size_t nbytes;
@@ -4143,6 +4184,11 @@ handle_tracepoint_general_set (char *packet)
       cmd_bigqtbuffer_circular (packet);
       return 1;
     }
+  else if (strncmp ("QTBuffer:size:", packet, strlen ("QTBuffer:size:")) == 0)
+    {
+      cmd_bigqtbuffer_size (packet);
+      return 1;
+    }
   else if (strncmp ("QTNotes:", packet, strlen ("QTNotes:")) == 0)
     {
       cmd_qtnotes (packet);
@@ -7228,10 +7274,8 @@ get_timestamp (void)
 void
 initialize_tracepoint (void)
 {
-  /* There currently no way to change the buffer size.  */
-  const int sizeOfBuffer = 5 * 1024 * 1024;
-  unsigned char *buf = xmalloc (sizeOfBuffer);
-  init_trace_buffer (buf, sizeOfBuffer);
+  /* Start with the default size.  */
+  init_trace_buffer (DEFAULT_TRACE_BUFFER_SIZE);
 
   /* Wire trace state variable 1 to be the timestamp.  This will be
      uploaded to GDB upon connection and become one of its trace state
diff --git a/gdb/remote.c b/gdb/remote.c
index 88a57c8..628419c 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -1284,6 +1284,7 @@ enum {
   PACKET_qXfer_fdpic,
   PACKET_QDisableRandomization,
   PACKET_QAgent,
+  PACKET_QTBuffer_size,
   PACKET_MAX
 };
 
@@ -3993,6 +3994,8 @@ static struct protocol_feature remote_protocol_features[] = {
   { "QDisableRandomization", PACKET_DISABLE, remote_supported_packet,
     PACKET_QDisableRandomization },
   { "QAgent", PACKET_DISABLE, remote_supported_packet, PACKET_QAgent},
+  { "QTBuffer:size", PACKET_DISABLE,
+    remote_supported_packet, PACKET_QTBuffer_size},
   { "tracenz", PACKET_DISABLE,
     remote_string_tracing_feature, -1 },
 };
@@ -11042,6 +11045,38 @@ remote_get_min_fast_tracepoint_insn_len (void)
     }
 }
 
+static void
+remote_set_trace_buffer_size (LONGEST val)
+{
+  if (remote_protocol_packets[PACKET_QTBuffer_size].support !=
+      PACKET_DISABLE)
+    {
+      struct remote_state *rs = get_remote_state ();
+      char *buf = rs->buf;
+      char *endbuf = rs->buf + get_remote_packet_size ();
+      enum packet_result result;
+
+      gdb_assert (val >= 0 || val == -1);
+      buf += xsnprintf (buf, endbuf - buf, "QTBuffer:size:");
+      /* Send -1 as literal "-1" to avoid host size dependency.  */
+      if (val < 0)
+	{
+	  *buf++ = '-';
+          buf += hexnumstr (buf, (ULONGEST) -val);
+	}
+      else
+	buf += hexnumstr (buf, (ULONGEST) val);
+
+      putpkt (rs->buf);
+      getpkt (&rs->buf, &rs->buf_size, 0);
+      result = packet_ok (rs->buf,
+		  &remote_protocol_packets[PACKET_QTBuffer_size]);
+
+      if (result != PACKET_OK)
+	warning (_("Bogus reply from target: %s"), rs->buf);
+    }
+}
+
 static int
 remote_set_trace_notes (char *user, char *notes, char *stop_notes)
 {
@@ -11219,6 +11254,7 @@ Specify the serial device it is connected to\n\
   remote_ops.to_get_min_fast_tracepoint_insn_len = remote_get_min_fast_tracepoint_insn_len;
   remote_ops.to_set_disconnected_tracing = remote_set_disconnected_tracing;
   remote_ops.to_set_circular_trace_buffer = remote_set_circular_trace_buffer;
+  remote_ops.to_set_trace_buffer_size = remote_set_trace_buffer_size;
   remote_ops.to_set_trace_notes = remote_set_trace_notes;
   remote_ops.to_core_of_thread = remote_core_of_thread;
   remote_ops.to_verify_memory = remote_verify_memory;
@@ -11755,6 +11791,9 @@ Show the maximum size of the address (in bits) in a memory packet."), NULL,
   add_packet_config_cmd (&remote_protocol_packets[PACKET_QAgent],
 			 "QAgent", "agent", 0);
 
+  add_packet_config_cmd (&remote_protocol_packets[PACKET_QTBuffer_size],
+			 "QTBuffer:size", "trace-buffer-size", 0);
+
   /* Keep the old ``set remote Z-packet ...'' working.  Each individual
      Z sub-packet has its own set and show commands, but users may
      have sets to this variable in their .gdbinit files (or in their
diff --git a/gdb/target.c b/gdb/target.c
index 9d8bf6e..2e507e0 100644
--- a/gdb/target.c
+++ b/gdb/target.c
@@ -693,6 +693,7 @@ update_current_target (void)
       INHERIT (to_get_min_fast_tracepoint_insn_len, t);
       INHERIT (to_set_disconnected_tracing, t);
       INHERIT (to_set_circular_trace_buffer, t);
+      INHERIT (to_set_trace_buffer_size, t);
       INHERIT (to_set_trace_notes, t);
       INHERIT (to_get_tib_address, t);
       INHERIT (to_set_permissions, t);
@@ -912,6 +913,9 @@ update_current_target (void)
   de_fault (to_set_circular_trace_buffer,
 	    (void (*) (int))
 	    target_ignore);
+  de_fault (to_set_trace_buffer_size,
+	    (void (*) (LONGEST))
+	    target_ignore);
   de_fault (to_set_trace_notes,
 	    (int (*) (char *, char *, char *))
 	    return_zero);
diff --git a/gdb/target.h b/gdb/target.h
index 1971265..c99642d 100644
--- a/gdb/target.h
+++ b/gdb/target.h
@@ -806,6 +806,8 @@ struct target_ops
        disconnection - set VAL to 1 to keep tracing, 0 to stop.  */
     void (*to_set_disconnected_tracing) (int val);
     void (*to_set_circular_trace_buffer) (int val);
+    /* Set the size of trace buffer in the target.  */
+    void (*to_set_trace_buffer_size) (LONGEST val);
 
     /* Add/change textual notes about the trace run, returning 1 if
        successful, 0 otherwise.  */
@@ -1700,6 +1702,9 @@ extern char *target_fileio_read_stralloc (const char *filename);
 #define	target_set_circular_trace_buffer(val)	\
   (*current_target.to_set_circular_trace_buffer) (val)
 
+#define	target_set_trace_buffer_size(val)	\
+  (*current_target.to_set_trace_buffer_size) (val)
+
 #define	target_set_trace_notes(user,notes,stopnotes)		\
   (*current_target.to_set_trace_notes) ((user), (notes), (stopnotes))
 
diff --git a/gdb/testsuite/gdb.trace/trace-buffer-size.c b/gdb/testsuite/gdb.trace/trace-buffer-size.c
new file mode 100644
index 0000000..e32b756
--- /dev/null
+++ b/gdb/testsuite/gdb.trace/trace-buffer-size.c
@@ -0,0 +1,31 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2011-2013 Free Software Foundation, Inc.
+
+   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/>.  */
+
+int var = 10;
+
+int
+test_function ()
+{
+  return 0;
+}
+
+int
+main ()
+{
+  test_function (); 
+  return 0; /*breakpoint1*/
+}
diff --git a/gdb/testsuite/gdb.trace/trace-buffer-size.exp b/gdb/testsuite/gdb.trace/trace-buffer-size.exp
new file mode 100644
index 0000000..9528fb3
--- /dev/null
+++ b/gdb/testsuite/gdb.trace/trace-buffer-size.exp
@@ -0,0 +1,105 @@
+# Copyright 1998-2013 Free Software Foundation, Inc.
+
+# 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/>.
+
+load_lib "trace-support.exp"
+
+standard_testfile
+
+if [prepare_for_testing ${testfile}.exp $testfile $srcfile \
+        {debug nowarnings}] {
+    untested "failed to prepare for trace tests"
+    return -1
+}
+
+if ![runto_main] {
+    fail "can't run to main to check for trace support"
+    return -1
+}
+
+if ![gdb_target_supports_trace] {
+    unsupported "target does not support trace"
+    return -1;
+}
+
+set BUFFER_SIZE 4
+
+# Save default trace buffer size in 'default_size'.
+gdb_test_multiple "tstatus" "tstatus check 1" {
+    -re ".*Trace buffer has ($decimal) bytes of ($decimal) bytes free.*" {
+        set default_size $expect_out(2,string)
+    }
+}
+
+# Change buffer size to 'BUFFER_SIZE'.
+gdb_test_no_output \
+  "set trace-buffer-size $BUFFER_SIZE" \
+  "set trace buffer size 1"
+
+gdb_test "tstatus" \
+  ".*Trace buffer has $decimal bytes of $BUFFER_SIZE bytes free.*" \
+  "tstatus check 2"
+
+gdb_test "show trace-buffer-size $BUFFER_SIZE" \
+  "Requested size of trace buffer is $BUFFER_SIZE.*" \
+  "show trace buffer size"
+
+gdb_test_no_output \
+  "set trace-buffer-size -1" \
+  "set trace buffer size 2"
+
+# Test that tstatus gives us default buffer size now.
+gdb_test "tstatus" \
+  ".*Trace buffer has $decimal bytes of $default_size bytes free.*" \
+  "tstatus check 3"
+
+gdb_test_no_output \
+  "set trace-buffer-size $BUFFER_SIZE" \
+  "set trace buffer size 3"
+
+# We set trace buffer to very small size.  Then after running trace,
+# we check if it is full.  This will show if setting trace buffer
+# size really worked.
+gdb_breakpoint ${srcfile}:[gdb_get_line_number "breakpoint1"]
+gdb_test "trace test_function" \
+  "Tracepoint \[0-9\]+ at .*" \
+  "set tracepoint at test_function"
+gdb_trace_setactions "Set action for trace point 1" "" \
+  "collect var" "^$"
+gdb_test_no_output "tstart" 
+gdb_test "continue" \
+  "Continuing.*Breakpoint $decimal.*" \
+  "run trace experiment 1"
+gdb_test "tstatus" \
+  ".*Trace stopped because the buffer was full.*" \
+  "buffer full check 1"
+
+# Use the default size -- the trace buffer should not end up
+# full this time
+clean_restart ${testfile}
+runto_main
+gdb_breakpoint ${srcfile}:[gdb_get_line_number "breakpoint1"]
+gdb_test "trace test_function" \
+  "Tracepoint \[0-9\]+ at .*" \
+  "set tracepoint at test_function"
+gdb_trace_setactions "Set action for trace point 2" "" \
+  "collect var" "^$"
+gdb_test_no_output "tstart" 
+gdb_test "continue" \
+  "Continuing.*Breakpoint $decimal.*" \
+  "run trace experiment 2"
+gdb_test "tstatus" \
+  ".*Trace is running on the target.*" \
+  "buffer full check 2"
+gdb_test_no_output "tstop"
diff --git a/gdb/tracepoint.c b/gdb/tracepoint.c
index 9a80aa3..b8945bb 100644
--- a/gdb/tracepoint.c
+++ b/gdb/tracepoint.c
@@ -173,6 +173,11 @@ static int disconnected_tracing;
 
 static int circular_trace_buffer;
 
+/* This variable is the requested trace buffer size, or -1 to indicate
+   that we don't care and leave it up to the target to set a size.  */
+
+static int trace_buffer_size = -1;
+
 /* Textual notes applying to the current and/or future trace runs.  */
 
 char *trace_user = NULL;
@@ -1829,6 +1834,7 @@ start_tracing (char *notes)
   /* Set some mode flags.  */
   target_set_disconnected_tracing (disconnected_tracing);
   target_set_circular_trace_buffer (circular_trace_buffer);
+  target_set_trace_buffer_size (trace_buffer_size);
 
   if (!notes)
     notes = trace_notes;
@@ -3231,6 +3237,13 @@ set_circular_trace_buffer (char *args, int from_tty,
 }
 
 static void
+set_trace_buffer_size (char *args, int from_tty,
+			   struct cmd_list_element *c)
+{
+  target_set_trace_buffer_size (trace_buffer_size);
+}
+
+static void
 set_trace_user (char *args, int from_tty,
 		struct cmd_list_element *c)
 {
@@ -5416,6 +5429,16 @@ up and stopping the trace run."),
 			   &setlist,
 			   &showlist);
 
+  add_setshow_zuinteger_unlimited_cmd ("trace-buffer-size", no_class,
+			    &trace_buffer_size, _("\
+Set requested size of trace buffer."), _("\
+Show requested size of trace buffer."), _("\
+Use this to choose a size for the trace buffer.  Some targets\n\
+may have fixed or limited buffer sizes.  A value of -1 disables\n\
+any attempt to set the buffer size and lets the target choose."),
+			    set_trace_buffer_size, NULL,
+			    &setlist, &showlist);
+
   add_setshow_string_cmd ("trace-user", class_trace,
 			  &trace_user, _("\
 Set the user name to use for current and future trace runs"), _("\