Xserver provider for DTrace

Alan Coopersmith

Oracle Corporation
Solaris Engineering

X.Org Xserver version 1.9

Copyright (c) 2005, 2006, 2007, 2010, Oracle and/or its affiliates. All rights reserved.

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Table of Contents

Introduction
Available probes
Data Available in Probe Arguments
Examples

Introduction

This page provides details on a statically defined user application tracing provider for the DTrace facility in Solaris™ 10, MacOS X™ 10.5, and later releases. This provider instruments various points in the X server, to allow tracing what client applications are up to.

The provider was integrated into the X.Org git master repository with Solaris 10 & OpenSolaris support for the Xserver 1.4 release, released in 2007 with X11R7.3. Support for DTrace on MacOS X was added in Xserver 1.7.

These probes expose the request and reply structure of the X protocol between clients and the X server, so an understanding of that basic nature will aid in learning how to use these probes.

Available probes

Due to the way User-Defined DTrace probes work, arguments to these probes all bear undistinguished names of arg0, arg1, arg2, etc. These tables should help you determine what the real data is for each of the probe arguments.

Table 1. Probes and their arguments

Probe nameDescriptionarg0arg1arg2arg3arg4
Request Probes
request-startCalled just before processing each client request.requestNamerequestCoderequestLengthclientIdrequestBuffer
request-doneCalled just after processing each client request.requestNamerequestCodesequenceNumberclientIdresultCode
Event Probes
send-eventCalled just before send each event to a client.clientIdeventCodeeventBuffer  
Client Connection Probes
client-connectCalled when a new connection is opened from a clientclientIdclientFD   
client-authCalled when client authenticates (normally just after connection opened)clientIdclientAddrclientPidclientZoneId 
client-disconnectCalled when a client connection is closedclientId    
Resource Allocation Probes
resource-allocCalled when a new resource (pixmap, gc, colormap, etc.) is allocatedresourceIdresourceTypeIdresourceValueresourceTypeName 
resource-freeCalled when a resource is freedresourceIdresourceTypeIdresourceValueresourceTypeName 


Data Available in Probe Arguments

To access data in arguments of type string, you will need to use copyinstr(). To access data buffers referenced via uintptr_t's, you will need to use copyin().

Table 2. Probe Arguments

Argument nameTypeDescription
clientAddrstringString representing address client connected from
clientFDintX server's file descriptor for server side of each connection
clientIdintUnique integer identifier for each connection to the X server
clientPidpid_tProcess id of client, if connection is local (from getpeerucred())
clientZoneIdzoneid_tSolaris: Zone id of client, if connection is local (from getpeerucred())
eventBufferuintptr_tPointer to buffer containing X event - decode using structures in <X11/Xproto.h> and similar headers for each extension
eventCodeuint8_tEvent number of X event
resourceIduint32_tX resource id (XID)
resourceTypeIduint32_tResource type id
resourceTypeNamestringString representing X resource type ("PIXMAP", etc.)
resourceValueuintptr_tPointer to data for X resource
resultCodeintInteger code representing result status of request
requestBufferuintptr_tPointer to buffer containing X request - decode using structures in <X11/Xproto.h> and similar headers for each extension
requestCodeuint8_tRequest number of X request or Extension
requestNamestringName of X request or Extension
requestLengthuint16_tLength of X request
sequenceNumberuint32_tNumber of X request in in this connection


Examples

Example 1. Counting requests by request name

This script simply increments a counter for each different request made, and when you exit the script (such as by hitting Control+C) prints the counts.

#!/usr/sbin/dtrace -s

Xserver*:::request-start
{
    @counts[copyinstr(arg0)] = count();
}
	

The output from a short run may appear as:

  QueryPointer                                                      1
  CreatePixmap                                                      2
  FreePixmap                                                        2
  PutImage                                                          2
  ChangeGC                                                         10
  CopyArea                                                         10
  CreateGC                                                         14
  FreeGC                                                           14
  RENDER                                                           28
  SetClipRectangles                                                40
	

This can be rewritten slightly to cache the string containing the name of the request since it will be reused many times, instead of copying it over and over from the kernel:

#!/usr/sbin/dtrace -s

string Xrequest[uintptr_t];

Xserver*:::request-start
/Xrequest[arg0] == ""/
{
    Xrequest[arg0] = copyinstr(arg0);
}

Xserver*:::request-start
{
    @counts[Xrequest[arg0]] = count();
}
	


Example 2. Get average CPU time per request

This script records the CPU time used between the probes at the start and end of each request and aggregates it per request type.

#!/usr/sbin/dtrace -s

Xserver*:::request-start
{
    reqstart = vtimestamp;
}

Xserver*:::request-done
{
    @times[copyinstr(arg0)] = avg(vtimestamp - reqstart);
}
	

The output from a sample run might look like:

  ChangeGC                                                        889
  MapWindow                                                       907
  SetClipRectangles                                              1319
  PolyPoint                                                      1413
  PolySegment                                                    1434
  PolyRectangle                                                  1828
  FreeCursor                                                     1895
  FreeGC                                                         1950
  CreateGC                                                       2244
  FreePixmap                                                     2246
  GetInputFocus                                                  2249
  TranslateCoords                                                8508
  QueryTree                                                      8846
  GetGeometry                                                    9948
  CreatePixmap                                                  12111
  AllowEvents                                                   14090
  GrabServer                                                    14791
  MIT-SCREEN-SAVER                                              16747
  ConfigureWindow                                               22917
  SetInputFocus                                                 28521
  PutImage                                                     240841

	


Example 3. Monitoring clients that connect and disconnect

This script simply prints information about each client that connects or disconnects from the server while it is running. Since the provider is specified as Xserver$1 instead of Xserver* like previous examples, it won't monitor all Xserver processes running on the machine, but instead expects the process id of the X server to monitor to be specified as the argument to the script.

#!/usr/sbin/dtrace -s

Xserver$1:::client-connect
{
	printf("** Client Connect: id %d\n", arg0);
}

Xserver$1:::client-auth
{
	printf("** Client auth'ed: id %d => %s pid %d\n",
		arg0, copyinstr(arg1), arg2);
}

Xserver$1:::client-disconnect
{
	printf("** Client Disconnect: id %d\n", arg0);
}
	

A sample run:

# ./foo.d 5790
dtrace: script './foo.d' matched 4 probes
CPU     ID                    FUNCTION:NAME
  0  15774 CloseDownClient:client-disconnect ** Client Disconnect: id 65

  2  15774 CloseDownClient:client-disconnect ** Client Disconnect: id 64

  0  15773 EstablishNewConnections:client-connect ** Client Connect: id 64

  0  15772            AuthAudit:client-auth ** Client auth'ed: id 64 => local host pid 2034

  0  15773 EstablishNewConnections:client-connect ** Client Connect: id 65

  0  15772            AuthAudit:client-auth ** Client auth'ed: id 65 => local host pid 2034

  0  15774 CloseDownClient:client-disconnect ** Client Disconnect: id 64
	  
	


Example 4. Monitoring clients creating Pixmaps

This script can be used to determine which clients are creating pixmaps in the X server, printing information about each client as it connects to help trace it back to the program on the other end of the X connection.

#!/usr/sbin/dtrace -qs

string Xrequest[uintptr_t];
string Xrestype[uintptr_t];

Xserver$1:::request-start
/Xrequest[arg0] == ""/
{
	Xrequest[arg0] = copyinstr(arg0);
}

Xserver$1:::resource-alloc
/arg3 != 0 && Xrestype[arg3] == ""/
{
	Xrestype[arg3] = copyinstr(arg3);
}


Xserver$1:::request-start
/Xrequest[arg0] == "X_CreatePixmap"/
{
	printf("-> %s: client %d\n", Xrequest[arg0], arg3);
}

Xserver$1:::request-done
/Xrequest[arg0] == "X_CreatePixmap"/
{
	printf("<- %s: client %d\n", Xrequest[arg0], arg3);
}

Xserver$1:::resource-alloc
/Xrestype[arg3] == "PIXMAP"/
{
	printf("** Pixmap alloc: %08x\n", arg0);
}


Xserver$1:::resource-free
/Xrestype[arg3] == "PIXMAP"/
{
	printf("** Pixmap free:  %08x\n", arg0);
}

Xserver$1:::client-connect
{
	printf("** Client Connect: id %d\n", arg0);
}

Xserver$1:::client-auth
{
	printf("** Client auth'ed: id %d => %s pid %d\n",
		arg0, copyinstr(arg1), arg2);
}

Xserver$1:::client-disconnect
{
	printf("** Client Disconnect: id %d\n", arg0);
}
	

Sample output from a run of this script:


** Client Connect: id 17
** Client auth'ed: id 17 => local host pid 20273
-> X_CreatePixmap: client 17
** Pixmap alloc: 02200009
<- X_CreatePixmap: client 17
-> X_CreatePixmap: client 15
** Pixmap alloc: 01e00180
<- X_CreatePixmap: client 15
-> X_CreatePixmap: client 15
** Pixmap alloc: 01e00181
<- X_CreatePixmap: client 15
-> X_CreatePixmap: client 14
** Pixmap alloc: 01c004c8
<- X_CreatePixmap: client 14
** Pixmap free:  02200009
** Client Disconnect: id 17
** Pixmap free:  01e00180
** Pixmap free:  01e00181