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diff --git a/docs/docbook/devdoc/printing.xml b/docs/docbook/devdoc/printing.xml new file mode 100644 index 0000000000..363b9fb6e5 --- /dev/null +++ b/docs/docbook/devdoc/printing.xml @@ -0,0 +1,393 @@ +<chapter id="printing"> +<chapterinfo> + <author> + <firstname>Gerald</firstname><surname>Carter</surname> + </author> + <pubdate>October 2002</pubdate> +</chapterinfo> + + +<title>Samba Printing Internals</title> + + +<sect1> +<title>Abstract</title> +<para> +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. +</para> +</sect1> + + + +<sect1> +<title> +Printing Interface to Various Back ends +</title> + +<para> +Samba uses a table of function pointers to seven functions. The +function prototypes are defined in the <varname>printif</varname> structure declared +in <filename>printing.h</filename>. +</para> + +<itemizedlist> + <listitem><para>retrieve the contents of a print queue</para></listitem> + <listitem><para>pause the print queue</para></listitem> + <listitem><para>resume a paused print queue</para></listitem> + <listitem><para>delete a job from the queue</para></listitem> + <listitem><para>pause a job in the print queue</para></listitem> + <listitem><para>result a paused print job in the queue</para></listitem> + <listitem><para>submit a job to the print queue</para></listitem> +</itemizedlist> + +<para> +Currently there are only two printing back end implementations +defined. +</para> + +<itemizedlist> + <listitem><para>a generic set of functions for working with standard UNIX + printing subsystems</para></listitem> + + <listitem><para>a set of CUPS specific functions (this is only enabled if + the CUPS libraries were located at compile time).</para></listitem> +</itemizedlist> + +</sect1> + + + + +<sect1> +<title> +Print Queue TDB's +</title> + + +<para> +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. +</para> + +<para> +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. +</para> + +<para> +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". +</para> + +<para><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; +}; +</programlisting></para> + +<para> +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. +</para> + +<para> +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. +</para> + +<para> +When updating a print queue, smbd will perform the following +steps ( refer to <filename>print.c:print_queue_update()</filename> ): +</para> + +<orderedlist> + <listitem><para>Check to see if another smbd is currently in + the process of updating the queue contents by checking the pid + stored in <constant>LOCK/<replaceable>printer_name</replaceable></constant>. + If so, then do not update the TDB.</para></listitem> + + <listitem><para>Lock the mutex entry in the TDB and store our own pid. + Check that this succeeded, else fail.</para></listitem> + + <listitem><para>Store the updated time stamp for the new cache + listing</para></listitem> + + <listitem><para>Retrieve the queue listing via "lpq command"</para></listitem> + + <listitem><para><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 + } + }</programlisting></para></listitem> + + <listitem><para>Delete any jobs in the TDB that are not + in the in the lpq listing</para></listitem> + + <listitem><para>Store the print queue status in the TDB</para></listitem> + + <listitem><para>update the cache time stamp again</para></listitem> + +</orderedlist> + +<para> +Note that it is the contents of this TDB that is returned to Windows +clients and not the actual listing from the "lpq command". +</para> + +<para> +The NT_DEVICEMODE stored as part of the printjob structure is used to +store a pointer to a non-default DeviceMode associated with the print +job. The pointer will be non-null when the client included a Device +Mode in the OpenPrinterEx() call and subsequently submitted a job for +printing on that same handle. If the client did not include a Device +Mode in the OpenPrinterEx() request, the nt_devmode field is NULL +and the job has the printer's device mode associated with it by default. +</para> + +<para> +Only non-default Device Mode are stored with print jobs in the print +queue TDB. Otherwise, the Device Mode is obtained from the printer +object when the client issues a GetJob(level == 2) request. +</para> + +</sect1> + + + + +<sect1> +<title> +ChangeID and Client Caching of Printer Information +</title> + +<para> +[To be filled in later] +</para> +</sect1> + + + +<sect1> +<title> +Windows NT/2K Printer Change Notify +</title> + +<para> +When working with Windows NT+ clients, it is possible for a +print server to use RPC to send asynchronous change notification +events to clients for certain printer and print job attributes. +This can be useful when the client needs to know that a new +job has been added to the queue for a given printer or that the +driver for a printer has been changed. Note that this is done +entirely orthogonal to cache updates based on a new ChangeID for +a printer object. +</para> + +<para> +The basic set of RPC's used to implement change notification are +</para> + +<itemizedlist> + <listitem><para>RemoteFindFirstPrinterChangeNotifyEx ( RFFPCN )</para></listitem> + <listitem><para>RemoteFindNextPrinterChangeNotifyEx ( RFNPCN )</para></listitem> + <listitem><para>FindClosePrinterChangeNotify( FCPCN )</para></listitem> + <listitem><para>ReplyOpenPrinter</para></listitem> + <listitem><para>ReplyClosePrinter</para></listitem> + <listitem><para>RouteRefreshPrinterChangeNotify ( RRPCN )</para></listitem> +</itemizedlist> + +<para> +One additional RPC is available to a server, but is never used by the +Windows spooler service: +</para> + +<itemizedlist> + <listitem><para>RouteReplyPrinter()</para></listitem> +</itemizedlist> + +<para> +The opnum for all of these RPC's are defined in include/rpc_spoolss.h +</para> + +<para> +Windows NT print servers use a bizarre method of sending print +notification event to clients. The process of registering a new change +notification handle is as follows. The 'C' is for client and the +'S' is for server. All error conditions have been eliminated. +</para> + +<para><programlisting> +C: Obtain handle to printer or to the printer + server via the standard OpenPrinterEx() call. +S: Respond with a valid handle to object + +C: Send a RFFPCN request with the previously obtained + handle with either (a) set of flags for change events + to monitor, or (b) a PRINTER_NOTIFY_OPTIONS structure + containing the event information to monitor. The windows + spooler has only been observed to use (b). +S: The <* another missing word*> opens a new TCP session to the client (thus requiring + all print clients to be CIFS servers as well) and sends + a ReplyOpenPrinter() request to the client. +C: The client responds with a printer handle that can be used to + send event notification messages. +S: The server replies success to the RFFPCN request. + +C: The windows spooler follows the RFFPCN with a RFNPCN + request to fetch the current values of all monitored + attributes. +S: The server replies with an array SPOOL_NOTIFY_INFO_DATA + structures (contained in a SPOOL_NOTIFY_INFO structure). + +C: If the change notification handle is ever released by the + client via a FCPCN request, the server sends a ReplyClosePrinter() + request back to the client first. However a request of this + nature from the client is often an indication that the previous + notification event was not marshalled correctly by the server + or a piece of data was wrong. +S: The server closes the internal change notification handle + (POLICY_HND) and does not send any further change notification + events to the client for that printer or job. +</programlisting></para> + +<para> +The current list of notification events supported by Samba can be +found by examining the internal tables in srv_spoolss_nt.c +</para> + +<itemizedlist> + <listitem><para>printer_notify_table[]</para></listitem> + <listitem><para>job_notify_table[]</para></listitem> +</itemizedlist> + +<para> +When an event occurs that could be monitored, smbd sends a message +to itself about the change. The list of events to be transmitted +are queued by the smbd process sending the message to prevent an +overload of TDB usage and the internal message is sent during smbd's +idle loop (refer to printing/notify.c and the functions +send_spoolss_notify2_msg() and print_notify_send_messages() ). +</para> + +<para> +The decision of whether or not the change is to be sent to connected +clients is made by the routine which actually sends the notification. +( refer to srv_spoolss_nt.c:recieve_notify2_message() ). +</para> + +<para> +Because it possible to receive a listing of multiple changes for +multiple printers, the notification events must be split into +categories by the printer name. This makes it possible to group +multiple change events to be sent in a single RPC according to the +printer handle obtained via a ReplyOpenPrinter(). +</para> + +<para> +The actual change notification is performed using the RRPCN request +RPC. This packet contains +</para> + + +<itemizedlist> + +<listitem><para>the printer handle registered with the +client's spooler on which the change occurred</para></listitem> + +<listitem><para>The change_low value which was sent as part +of the last RFNPCN request from the client</para></listitem> + +<listitem><para>The SPOOL_NOTIFY_INFO container with the event +information</para></listitem> + +</itemizedlist> + +<para> +A <varname>SPOOL_NOTIFY_INFO</varname> contains: +</para> + +<itemizedlist> + +<listitem><para>the version and flags field are predefined +and should not be changed</para></listitem> + +<listitem><para>The count field is the number of entries +in the SPOOL_NOTIFY_INFO_DATA array</para></listitem> + +</itemizedlist> + +<para> +The <varname>SPOOL_NOTIFY_INFO_DATA</varname> entries contain: +</para> + +<itemizedlist> + +<listitem><para>The type defines whether or not this event +is for a printer or a print job</para></listitem> + +<listitem><para>The field is the flag identifying the event</para></listitem> + +<listitem><para>the notify_data union contains the new valuie of the +attribute</para></listitem> + +<listitem><para>The enc_type defines the size of the structure for marshalling +and unmarshalling</para></listitem> + +<listitem><para>(a) the id must be 0 for a printer event on a printer handle. +(b) the id must be the job id for an event on a printer job +(c) the id must be the matching number of the printer index used +in the response packet to the RFNPCN when using a print server +handle for notification. Samba currently uses the snum of +the printer for this which can break if the list of services +has been modified since the notification handle was registered.</para></listitem> + +<listitem><para>The size is either (a) the string length in UNICODE for strings, +(b) the size in bytes of the security descriptor, or (c) 0 for +data values.</para></listitem> + +</itemizedlist> + +</sect1> +</chapter> |