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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 V1.75.2"><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" title="Chapter 15. Samba Printing Internals"><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#id332767">Abstract</a></span></dt><dt><span class="sect1"><a href="devprinting.html#id332778">
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Printing Interface to Various Back ends
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</a></span></dt><dt><span class="sect1"><a href="devprinting.html#id332848">
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Print Queue TDB's
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</a></span></dt><dt><span class="sect1"><a href="devprinting.html#id332986">
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ChangeID and Client Caching of Printer Information
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</a></span></dt><dt><span class="sect1"><a href="devprinting.html#id332995">
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Windows NT/2K Printer Change Notify
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</a></span></dt></dl></div><div class="sect1" title="Abstract"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id332767"></a>Abstract</h2></div></div></div><p>
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The purpose of this document is to provide some insight into
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Samba's printing functionality and also to describe the semantics
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of certain features of Windows client printing.
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</p></div><div class="sect1" title="Printing Interface to Various Back ends"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id332778"></a>
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Printing Interface to Various Back ends
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</h2></div></div></div><p>
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Samba uses a table of function pointers to seven functions. The
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function prototypes are defined in the <code class="varname">printif</code> structure declared
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in <code class="filename">printing.h</code>.
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</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>retrieve the contents of a print queue</p></li><li class="listitem"><p>pause the print queue</p></li><li class="listitem"><p>resume a paused print queue</p></li><li class="listitem"><p>delete a job from the queue</p></li><li class="listitem"><p>pause a job in the print queue</p></li><li class="listitem"><p>result a paused print job in the queue</p></li><li class="listitem"><p>submit a job to the print queue</p></li></ul></div><p>
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Currently there are only two printing back end implementations
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defined.
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</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>a generic set of functions for working with standard UNIX
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printing subsystems</p></li><li class="listitem"><p>a set of CUPS specific functions (this is only enabled if
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the CUPS libraries were located at compile time).</p></li></ul></div></div><div class="sect1" title="Print Queue TDB's"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id332848"></a>
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Print Queue TDB's
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</h2></div></div></div><p>
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Samba provides periodic caching of the output from the "lpq command"
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for performance reasons. This cache time is configurable in seconds.
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Obviously the longer the cache time the less often smbd will be
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required to exec a copy of lpq. However, the accuracy of the print
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queue contents displayed to clients will be diminished as well.
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</p><p>
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The list of currently opened print queue TDB's can be found
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be examining the list of tdb_print_db structures ( see print_db_head
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in printing.c ). A queue TDB is opened using the wrapper function
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printing.c:get_print_db_byname(). The function ensures that smbd
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does not open more than MAX_PRINT_DBS_OPEN in an effort to prevent
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a large print server from exhausting all available file descriptors.
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If the number of open queue TDB's exceeds the MAX_PRINT_DBS_OPEN
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limit, smbd falls back to a most recently used algorithm for maintaining
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a list of open TDB's.
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</p><p>
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There are two ways in which a a print job can be entered into
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a print queue's TDB. The first is to submit the job from a Windows
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client which will insert the job information directly into the TDB.
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The second method is to have the print job picked up by executing the
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"lpq command".
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</p><pre class="programlisting">
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/* included from printing.h */
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struct printjob {
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pid_t pid; /* which process launched the job */
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int sysjob; /* the system (lp) job number */
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int fd; /* file descriptor of open file if open */
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time_t starttime; /* when the job started spooling */
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int status; /* the status of this job */
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size_t size; /* the size of the job so far */
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int page_count; /* then number of pages so far */
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BOOL spooled; /* has it been sent to the spooler yet? */
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BOOL smbjob; /* set if the job is a SMB job */
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fstring filename; /* the filename used to spool the file */
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fstring jobname; /* the job name given to us by the client */
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fstring user; /* the user who started the job */
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fstring queuename; /* service number of printer for this job */
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NT_DEVICEMODE *nt_devmode;
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};
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</pre><p>
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The current manifestation of the printjob structure contains a field
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for the UNIX job id returned from the "lpq command" and a Windows job
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ID (32-bit bounded by PRINT_MAX_JOBID). When a print job is returned
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by the "lpq command" that does not match an existing job in the queue's
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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
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the id reported by lpq.
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</p><p>
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In order to match a 32-bit Windows jobid onto a 16-bit lanman print job
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id, smbd uses an in memory TDB to match the former to a number appropriate
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for old lanman clients.
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</p><p>
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When updating a print queue, smbd will perform the following
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steps ( refer to <code class="filename">print.c:print_queue_update()</code> ):
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</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>Check to see if another smbd is currently in
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the process of updating the queue contents by checking the pid
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stored in <code class="constant">LOCK/<em class="replaceable"><code>printer_name</code></em></code>.
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If so, then do not update the TDB.</p></li><li class="listitem"><p>Lock the mutex entry in the TDB and store our own pid.
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Check that this succeeded, else fail.</p></li><li class="listitem"><p>Store the updated time stamp for the new cache
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listing</p></li><li class="listitem"><p>Retrieve the queue listing via "lpq command"</p></li><li class="listitem"><pre class="programlisting">
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foreach job in the queue
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{
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if the job is a UNIX job, create a new entry;
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if the job has a Windows based jobid, then
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{
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Lookup the record by the jobid;
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if the lookup failed, then
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treat it as a UNIX job;
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else
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update the job status only
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}
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}</pre></li><li class="listitem"><p>Delete any jobs in the TDB that are not
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in the in the lpq listing</p></li><li class="listitem"><p>Store the print queue status in the TDB</p></li><li class="listitem"><p>update the cache time stamp again</p></li></ol></div><p>
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Note that it is the contents of this TDB that is returned to Windows
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clients and not the actual listing from the "lpq command".
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</p><p>
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The NT_DEVICEMODE stored as part of the printjob structure is used to
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store a pointer to a non-default DeviceMode associated with the print
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job. The pointer will be non-null when the client included a Device
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Mode in the OpenPrinterEx() call and subsequently submitted a job for
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printing on that same handle. If the client did not include a Device
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Mode in the OpenPrinterEx() request, the nt_devmode field is NULL
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and the job has the printer's device mode associated with it by default.
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</p><p>
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Only non-default Device Mode are stored with print jobs in the print
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queue TDB. Otherwise, the Device Mode is obtained from the printer
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object when the client issues a GetJob(level == 2) request.
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</p></div><div class="sect1" title="ChangeID and Client Caching of Printer Information"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id332986"></a>
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ChangeID and Client Caching of Printer Information
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</h2></div></div></div><p>
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[To be filled in later]
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</p></div><div class="sect1" title="Windows NT/2K Printer Change Notify"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id332995"></a>
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Windows NT/2K Printer Change Notify
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</h2></div></div></div><p>
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When working with Windows NT+ clients, it is possible for a
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print server to use RPC to send asynchronous change notification
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events to clients for certain printer and print job attributes.
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This can be useful when the client needs to know that a new
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job has been added to the queue for a given printer or that the
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driver for a printer has been changed. Note that this is done
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entirely orthogonal to cache updates based on a new ChangeID for
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a printer object.
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</p><p>
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The basic set of RPC's used to implement change notification are
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</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>RemoteFindFirstPrinterChangeNotifyEx ( RFFPCN )</p></li><li class="listitem"><p>RemoteFindNextPrinterChangeNotifyEx ( RFNPCN )</p></li><li class="listitem"><p>FindClosePrinterChangeNotify( FCPCN )</p></li><li class="listitem"><p>ReplyOpenPrinter</p></li><li class="listitem"><p>ReplyClosePrinter</p></li><li class="listitem"><p>RouteRefreshPrinterChangeNotify ( RRPCN )</p></li></ul></div><p>
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One additional RPC is available to a server, but is never used by the
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Windows spooler service:
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</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>RouteReplyPrinter()</p></li></ul></div><p>
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The opnum for all of these RPC's are defined in include/rpc_spoolss.h
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</p><p>
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Windows NT print servers use a bizarre method of sending print
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notification event to clients. The process of registering a new change
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notification handle is as follows. The 'C' is for client and the
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'S' is for server. All error conditions have been eliminated.
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</p><pre class="programlisting">
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C: Obtain handle to printer or to the printer
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server via the standard OpenPrinterEx() call.
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S: Respond with a valid handle to object
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C: Send a RFFPCN request with the previously obtained
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handle with either (a) set of flags for change events
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to monitor, or (b) a PRINTER_NOTIFY_OPTIONS structure
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containing the event information to monitor. The windows
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spooler has only been observed to use (b).
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S: The <* another missing word*> opens a new TCP session to the client (thus requiring
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all print clients to be CIFS servers as well) and sends
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a ReplyOpenPrinter() request to the client.
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C: The client responds with a printer handle that can be used to
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send event notification messages.
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S: The server replies success to the RFFPCN request.
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C: The windows spooler follows the RFFPCN with a RFNPCN
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request to fetch the current values of all monitored
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attributes.
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S: The server replies with an array SPOOL_NOTIFY_INFO_DATA
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structures (contained in a SPOOL_NOTIFY_INFO structure).
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C: If the change notification handle is ever released by the
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client via a FCPCN request, the server sends a ReplyClosePrinter()
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request back to the client first. However a request of this
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nature from the client is often an indication that the previous
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notification event was not marshalled correctly by the server
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or a piece of data was wrong.
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S: The server closes the internal change notification handle
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(POLICY_HND) and does not send any further change notification
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events to the client for that printer or job.
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</pre><p>
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The current list of notification events supported by Samba can be
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found by examining the internal tables in srv_spoolss_nt.c
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</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>printer_notify_table[]</p></li><li class="listitem"><p>job_notify_table[]</p></li></ul></div><p>
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When an event occurs that could be monitored, smbd sends a message
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to itself about the change. The list of events to be transmitted
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are queued by the smbd process sending the message to prevent an
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overload of TDB usage and the internal message is sent during smbd's
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idle loop (refer to printing/notify.c and the functions
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send_spoolss_notify2_msg() and print_notify_send_messages() ).
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</p><p>
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The decision of whether or not the change is to be sent to connected
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clients is made by the routine which actually sends the notification.
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( refer to srv_spoolss_nt.c:recieve_notify2_message() ).
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</p><p>
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Because it possible to receive a listing of multiple changes for
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multiple printers, the notification events must be split into
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categories by the printer name. This makes it possible to group
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multiple change events to be sent in a single RPC according to the
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printer handle obtained via a ReplyOpenPrinter().
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</p><p>
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The actual change notification is performed using the RRPCN request
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RPC. This packet contains
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</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>the printer handle registered with the
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client's spooler on which the change occurred</p></li><li class="listitem"><p>The change_low value which was sent as part
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of the last RFNPCN request from the client</p></li><li class="listitem"><p>The SPOOL_NOTIFY_INFO container with the event
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information</p></li></ul></div><p>
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A <code class="varname">SPOOL_NOTIFY_INFO</code> contains:
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</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>the version and flags field are predefined
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and should not be changed</p></li><li class="listitem"><p>The count field is the number of entries
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in the SPOOL_NOTIFY_INFO_DATA array</p></li></ul></div><p>
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The <code class="varname">SPOOL_NOTIFY_INFO_DATA</code> entries contain:
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</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>The type defines whether or not this event
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is for a printer or a print job</p></li><li class="listitem"><p>The field is the flag identifying the event</p></li><li class="listitem"><p>the notify_data union contains the new valuie of the
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attribute</p></li><li class="listitem"><p>The enc_type defines the size of the structure for marshalling
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and unmarshalling</p></li><li class="listitem"><p>(a) the id must be 0 for a printer event on a printer handle.
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(b) the id must be the job id for an event on a printer job
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(c) the id must be the matching number of the printer index used
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in the response packet to the RFNPCN when using a print server
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handle for notification. Samba currently uses the snum of
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the printer for this which can break if the list of services
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has been modified since the notification handle was registered.</p></li><li class="listitem"><p>The size is either (a) the string length in UNICODE for strings,
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(b) the size in bytes of the security descriptor, or (c) 0 for
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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>
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