Xserver provider for DTrace

Alan Coopersmith

Oracle Corporation
Solaris Engineering

X.Org Xserver version 1.10.2

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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 name    | Description |   arg0    |     arg1     |     arg2     |      arg3      |    arg4     |
|--------------------------------------------------------------------------------------------------------|
|Request Probes                                                                                          |
|--------------------------------------------------------------------------------------------------------|
|                 |Called just  |           |              |              |                |             |
|                 |before       |           |              |              |                |             |
|request-start    |processing   |requestName|requestCode   |requestLength |clientId        |requestBuffer|
|                 |each client  |           |              |              |                |             |
|                 |request.     |           |              |              |                |             |
|-----------------+-------------+-----------+--------------+--------------+----------------+-------------|
|                 |Called just  |           |              |              |                |             |
|                 |after        |           |              |              |                |             |
|request-done     |processing   |requestName|requestCode   |sequenceNumber|clientId        |resultCode   |
|                 |each client  |           |              |              |                |             |
|                 |request.     |           |              |              |                |             |
|--------------------------------------------------------------------------------------------------------|
|Event Probes                                                                                            |
|--------------------------------------------------------------------------------------------------------|
|                 |Called just  |           |              |              |                |             |
|send-event       |before send  |clientId   |eventCode     |eventBuffer   |                |             |
|                 |each event to|           |              |              |                |             |
|                 |a client.    |           |              |              |                |             |
|--------------------------------------------------------------------------------------------------------|
|Client Connection Probes                                                                                |
|--------------------------------------------------------------------------------------------------------|
|                 |Called when a|           |              |              |                |             |
|                 |new          |           |              |              |                |             |
|client-connect   |connection is|clientId   |clientFD      |              |                |             |
|                 |opened from a|           |              |              |                |             |
|                 |client       |           |              |              |                |             |
|-----------------+-------------+-----------+--------------+--------------+----------------+-------------|
|                 |Called when  |           |              |              |                |             |
|                 |client       |           |              |              |                |             |
|                 |authenticates|           |              |              |                |             |
|client-auth      |(normally    |clientId   |clientAddr    |clientPid     |clientZoneId    |             |
|                 |just after   |           |              |              |                |             |
|                 |connection   |           |              |              |                |             |
|                 |opened)      |           |              |              |                |             |
|-----------------+-------------+-----------+--------------+--------------+----------------+-------------|
|                 |Called when a|           |              |              |                |             |
|client-disconnect|client       |clientId   |              |              |                |             |
|                 |connection is|           |              |              |                |             |
|                 |closed       |           |              |              |                |             |
|--------------------------------------------------------------------------------------------------------|
|Resource Allocation Probes                                                                              |
|--------------------------------------------------------------------------------------------------------|
|                 |Called when a|           |              |              |                |             |
|                 |new resource |           |              |              |                |             |
|resource-alloc   |(pixmap, gc, |resourceId |resourceTypeId|resourceValue |resourceTypeName|             |
|                 |colormap,    |           |              |              |                |             |
|                 |etc.) is     |           |              |              |                |             |
|                 |allocated    |           |              |              |                |             |
|-----------------+-------------+-----------+--------------+--------------+----------------+-------------|
|                 |Called when a|           |              |              |                |             |
|resource-free    |resource is  |resourceId |resourceTypeId|resourceValue |resourceTypeName|             |
|                 |freed        |           |              |              |                |             |
+--------------------------------------------------------------------------------------------------------+


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 name  |  Type   |                   Description                    |
|----------------+---------+--------------------------------------------------|
|clientAddr      |string   |String representing address client connected from |
|----------------+---------+--------------------------------------------------|
|clientFD        |int      |X server's file descriptor for server side of each|
|                |         |connection                                        |
|----------------+---------+--------------------------------------------------|
|clientId        |int      |Unique integer identifier for each connection to  |
|                |         |the X server                                      |
|----------------+---------+--------------------------------------------------|
|clientPid       |pid_t    |Process id of client, if connection is local (from|
|                |         |getpeerucred())                                   |
|----------------+---------+--------------------------------------------------|
|clientZoneId    |zoneid_t |Solaris: Zone id of client, if connection is local|
|                |         |(from getpeerucred())                             |
|----------------+---------+--------------------------------------------------|
|                |         |Pointer to buffer containing X event - decode     |
|eventBuffer     |uintptr_t|using structures in <X11/Xproto.h> and similar    |
|                |         |headers for each extension                        |
|----------------+---------+--------------------------------------------------|
|eventCode       |uint8_t  |Event number of X event                           |
|----------------+---------+--------------------------------------------------|
|resourceId      |uint32_t |X resource id (XID)                               |
|----------------+---------+--------------------------------------------------|
|resourceTypeId  |uint32_t |Resource type id                                  |
|----------------+---------+--------------------------------------------------|
|resourceTypeName|string   |String representing X resource type ("PIXMAP",    |
|                |         |etc.)                                             |
|----------------+---------+--------------------------------------------------|
|resourceValue   |uintptr_t|Pointer to data for X resource                    |
|----------------+---------+--------------------------------------------------|
|resultCode      |int      |Integer code representing result status of request|
|----------------+---------+--------------------------------------------------|
|                |         |Pointer to buffer containing X request - decode   |
|requestBuffer   |uintptr_t|using structures in <X11/Xproto.h> and similar    |
|                |         |headers for each extension                        |
|----------------+---------+--------------------------------------------------|
|requestCode     |uint8_t  |Request number of X request or Extension          |
|----------------+---------+--------------------------------------------------|
|requestName     |string   |Name of X request or Extension                    |
|----------------+---------+--------------------------------------------------|
|requestLength   |uint16_t |Length of X request                               |
|----------------+---------+--------------------------------------------------|
|sequenceNumber  |uint32_t |Number 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



