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<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Chapter�15.�Samba Printing Internals</title><link rel="stylesheet" href="../samba.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.74.0"><link rel="home" href="index.html" title="SAMBA Developers Guide"><link rel="up" href="pt04.html" title="Part�IV.�Debugging and tracing"><link rel="prev" href="tracing.html" title="Chapter�14.�Tracing samba system calls"><link rel="next" href="pt05.html" title="Part�V.�Appendices"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter�15.�Samba Printing Internals</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="tracing.html">Prev</a>�</td><th width="60%" align="center">Part�IV.�Debugging and tracing</th><td width="20%" align="right">�<a accesskey="n" href="pt05.html">Next</a></td></tr></table><hr></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="devprinting"></a>Chapter�15.�Samba Printing Internals</h2></div><div><div class="author"><h3 class="author"><span class="firstname">Gerald</span> <span class="surname">Carter</span></h3></div></div><div><p class="pubdate">October 2002</p></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="devprinting.html#id2561382">Abstract</a></span></dt><dt><span class="sect1"><a href="devprinting.html#id2561395">

Printing Interface to Various Back ends

</a></span></dt><dt><span class="sect1"><a href="devprinting.html#id2561471">

Print Queue TDB's

</a></span></dt><dt><span class="sect1"><a href="devprinting.html#id2561645">

ChangeID and Client Caching of Printer Information

</a></span></dt><dt><span class="sect1"><a href="devprinting.html#id2561655">

Windows NT/2K Printer Change Notify

</a></span></dt></dl></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2561382"></a>Abstract</h2></div></div></div><p>

The purpose of this document is to provide some insight into

Samba's printing functionality and also to describe the semantics

of certain features of Windows client printing.

</p></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2561395"></a>

Printing Interface to Various Back ends

</h2></div></div></div><p>

Samba uses a table of function pointers to seven functions. The

function prototypes are defined in the <code class="varname">printif</code> structure declared

in <code class="filename">printing.h</code>.

</p><div class="itemizedlist"><ul type="disc"><li><p>retrieve the contents of a print queue</p></li><li><p>pause the print queue</p></li><li><p>resume a paused print queue</p></li><li><p>delete a job from the queue</p></li><li><p>pause a job in the print queue</p></li><li><p>result a paused print job in the queue</p></li><li><p>submit a job to the print queue</p></li></ul></div><p>

Currently there are only two printing back end implementations

defined.

</p><div class="itemizedlist"><ul type="disc"><li><p>a generic set of functions for working with standard UNIX

printing subsystems</p></li><li><p>a set of CUPS specific functions (this is only enabled if

the CUPS libraries were located at compile time).</p></li></ul></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2561471"></a>

Print Queue TDB's

</h2></div></div></div><p>

Samba provides periodic caching of the output from the "lpq command"

for performance reasons. This cache time is configurable in seconds.

Obviously the longer the cache time the less often smbd will be

required to exec a copy of lpq. However, the accuracy of the print

queue contents displayed to clients will be diminished as well.

</p><p>

The list of currently opened print queue TDB's can be found

be examining the list of tdb_print_db structures ( see print_db_head

in printing.c ). A queue TDB is opened using the wrapper function

printing.c:get_print_db_byname(). The function ensures that smbd

does not open more than MAX_PRINT_DBS_OPEN in an effort to prevent

a large print server from exhausting all available file descriptors.

If the number of open queue TDB's exceeds the MAX_PRINT_DBS_OPEN

limit, smbd falls back to a most recently used algorithm for maintaining

a list of open TDB's.

</p><p>

There are two ways in which a a print job can be entered into

a print queue's TDB. The first is to submit the job from a Windows

client which will insert the job information directly into the TDB.

The second method is to have the print job picked up by executing the

"lpq command".

</p><pre class="programlisting">

/* included from printing.h */

struct printjob {

pid_t pid; /* which process launched the job */

int sysjob; /* the system (lp) job number */

int fd; /* file descriptor of open file if open */

time_t starttime; /* when the job started spooling */

int status; /* the status of this job */

size_t size; /* the size of the job so far */

int page_count; /* then number of pages so far */

BOOL spooled; /* has it been sent to the spooler yet? */

BOOL smbjob; /* set if the job is a SMB job */

fstring filename; /* the filename used to spool the file */

fstring jobname; /* the job name given to us by the client */

fstring user; /* the user who started the job */

fstring queuename; /* service number of printer for this job */

NT_DEVICEMODE *nt_devmode;

};

</pre><p>

The current manifestation of the printjob structure contains a field

for the UNIX job id returned from the "lpq command" and a Windows job

ID (32-bit bounded by PRINT_MAX_JOBID). When a print job is returned

by the "lpq command" that does not match an existing job in the queue's

TDB, a 32-bit job ID above the <*vance doesn't know what word is missing here*> is generating by adding UNIX_JOB_START to

the id reported by lpq.

</p><p>

In order to match a 32-bit Windows jobid onto a 16-bit lanman print job

id, smbd uses an in memory TDB to match the former to a number appropriate

for old lanman clients.

</p><p>

When updating a print queue, smbd will perform the following

steps ( refer to <code class="filename">print.c:print_queue_update()</code> ):

</p><div class="orderedlist"><ol type="1"><li><p>Check to see if another smbd is currently in

the process of updating the queue contents by checking the pid

stored in <code class="constant">LOCK/<em class="replaceable"><code>printer_name</code></em></code>.

If so, then do not update the TDB.</p></li><li><p>Lock the mutex entry in the TDB and store our own pid.

Check that this succeeded, else fail.</p></li><li><p>Store the updated time stamp for the new cache

listing</p></li><li><p>Retrieve the queue listing via "lpq command"</p></li><li><pre class="programlisting">

foreach job in the queue

{

if the job is a UNIX job, create a new entry;

if the job has a Windows based jobid, then

{

Lookup the record by the jobid;

if the lookup failed, then

treat it as a UNIX job;

else

update the job status only

}

}</pre></li><li><p>Delete any jobs in the TDB that are not

in the in the lpq listing</p></li><li><p>Store the print queue status in the TDB</p></li><li><p>update the cache time stamp again</p></li></ol></div><p>

Note that it is the contents of this TDB that is returned to Windows

100

clients and not the actual listing from the "lpq command".

101

</p><p>

102

The NT_DEVICEMODE stored as part of the printjob structure is used to

103

store a pointer to a non-default DeviceMode associated with the print

104

job. The pointer will be non-null when the client included a Device

105

Mode in the OpenPrinterEx() call and subsequently submitted a job for

106

printing on that same handle. If the client did not include a Device

107

Mode in the OpenPrinterEx() request, the nt_devmode field is NULL

108

and the job has the printer's device mode associated with it by default.

109

</p><p>

110

Only non-default Device Mode are stored with print jobs in the print

111

queue TDB. Otherwise, the Device Mode is obtained from the printer

112

object when the client issues a GetJob(level == 2) request.

113

</p></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2561645"></a>

114

ChangeID and Client Caching of Printer Information

115

</h2></div></div></div><p>

116

[To be filled in later]

117

</p></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2561655"></a>

118

Windows NT/2K Printer Change Notify

119

</h2></div></div></div><p>

120

When working with Windows NT+ clients, it is possible for a

121

print server to use RPC to send asynchronous change notification

122

events to clients for certain printer and print job attributes.

123

This can be useful when the client needs to know that a new

124

job has been added to the queue for a given printer or that the

125

driver for a printer has been changed. Note that this is done

126

entirely orthogonal to cache updates based on a new ChangeID for

127

a printer object.

128

</p><p>

129

The basic set of RPC's used to implement change notification are

130

</p><div class="itemizedlist"><ul type="disc"><li><p>RemoteFindFirstPrinterChangeNotifyEx ( RFFPCN )</p></li><li><p>RemoteFindNextPrinterChangeNotifyEx ( RFNPCN )</p></li><li><p>FindClosePrinterChangeNotify( FCPCN )</p></li><li><p>ReplyOpenPrinter</p></li><li><p>ReplyClosePrinter</p></li><li><p>RouteRefreshPrinterChangeNotify ( RRPCN )</p></li></ul></div><p>

131

One additional RPC is available to a server, but is never used by the

132

Windows spooler service:

133

</p><div class="itemizedlist"><ul type="disc"><li><p>RouteReplyPrinter()</p></li></ul></div><p>

134

The opnum for all of these RPC's are defined in include/rpc_spoolss.h

135

</p><p>

136

Windows NT print servers use a bizarre method of sending print

137

notification event to clients. The process of registering a new change

138

notification handle is as follows. The 'C' is for client and the

139

'S' is for server. All error conditions have been eliminated.

140

</p><pre class="programlisting">

141

C: Obtain handle to printer or to the printer

142

server via the standard OpenPrinterEx() call.

143

S: Respond with a valid handle to object

144

145

C: Send a RFFPCN request with the previously obtained

146

handle with either (a) set of flags for change events

147

to monitor, or (b) a PRINTER_NOTIFY_OPTIONS structure

148

containing the event information to monitor. The windows

149

spooler has only been observed to use (b).

150

S: The <* another missing word*> opens a new TCP session to the client (thus requiring

151

all print clients to be CIFS servers as well) and sends

152

a ReplyOpenPrinter() request to the client.

153

C: The client responds with a printer handle that can be used to

154

send event notification messages.

155

S: The server replies success to the RFFPCN request.

156

157

C: The windows spooler follows the RFFPCN with a RFNPCN

158

request to fetch the current values of all monitored

159

attributes.

160

S: The server replies with an array SPOOL_NOTIFY_INFO_DATA

161

structures (contained in a SPOOL_NOTIFY_INFO structure).

162

163

C: If the change notification handle is ever released by the

164

client via a FCPCN request, the server sends a ReplyClosePrinter()

165

request back to the client first. However a request of this

166

nature from the client is often an indication that the previous

167

notification event was not marshalled correctly by the server

168

or a piece of data was wrong.

169

S: The server closes the internal change notification handle

170

(POLICY_HND) and does not send any further change notification

171

events to the client for that printer or job.

172

</pre><p>

173

The current list of notification events supported by Samba can be

174

found by examining the internal tables in srv_spoolss_nt.c

175

</p><div class="itemizedlist"><ul type="disc"><li><p>printer_notify_table[]</p></li><li><p>job_notify_table[]</p></li></ul></div><p>

176

When an event occurs that could be monitored, smbd sends a message

177

to itself about the change. The list of events to be transmitted

178

are queued by the smbd process sending the message to prevent an

179

overload of TDB usage and the internal message is sent during smbd's

180

idle loop (refer to printing/notify.c and the functions

181

send_spoolss_notify2_msg() and print_notify_send_messages() ).

182

</p><p>

183

The decision of whether or not the change is to be sent to connected

184

clients is made by the routine which actually sends the notification.

185

( refer to srv_spoolss_nt.c:recieve_notify2_message() ).

186

</p><p>

187

Because it possible to receive a listing of multiple changes for

188

multiple printers, the notification events must be split into

189

categories by the printer name. This makes it possible to group

190

multiple change events to be sent in a single RPC according to the

191

printer handle obtained via a ReplyOpenPrinter().

192

</p><p>

193

The actual change notification is performed using the RRPCN request

194

RPC. This packet contains

195

</p><div class="itemizedlist"><ul type="disc"><li><p>the printer handle registered with the

196

client's spooler on which the change occurred</p></li><li><p>The change_low value which was sent as part

197

of the last RFNPCN request from the client</p></li><li><p>The SPOOL_NOTIFY_INFO container with the event

198

information</p></li></ul></div><p>

199

A <code class="varname">SPOOL_NOTIFY_INFO</code> contains:

200

</p><div class="itemizedlist"><ul type="disc"><li><p>the version and flags field are predefined

201

and should not be changed</p></li><li><p>The count field is the number of entries

202

in the SPOOL_NOTIFY_INFO_DATA array</p></li></ul></div><p>

203

The <code class="varname">SPOOL_NOTIFY_INFO_DATA</code> entries contain:

204

</p><div class="itemizedlist"><ul type="disc"><li><p>The type defines whether or not this event

205

is for a printer or a print job</p></li><li><p>The field is the flag identifying the event</p></li><li><p>the notify_data union contains the new valuie of the

206

attribute</p></li><li><p>The enc_type defines the size of the structure for marshalling

207

and unmarshalling</p></li><li><p>(a) the id must be 0 for a printer event on a printer handle.

208

(b) the id must be the job id for an event on a printer job

209

210

in the response packet to the RFNPCN when using a print server

211

handle for notification. Samba currently uses the snum of

212

the printer for this which can break if the list of services

213

has been modified since the notification handle was registered.</p></li><li><p>The size is either (a) the string length in UNICODE for strings,

214

(b) the size in bytes of the security descriptor, or (c) 0 for

215

data values.</p></li></ul></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="tracing.html">Prev</a>�</td><td width="20%" align="center"><a accesskey="u" href="pt04.html">Up</a></td><td width="40%" align="right">�<a accesskey="n" href="pt05.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter�14.�Tracing samba system calls�</td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top">�Part�V.�Appendices</td></tr></table></div></body></html>