<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html xmlns:fn="http://www.w3.org/2005/02/xpath-functions"> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <link rel="stylesheet" href="../../../../doc/otp_doc.css" type="text/css"> <title>Erlang -- Appendix B: The Backup Call Back Interface</title> </head> <body bgcolor="white" text="#000000" link="#0000ff" vlink="#ff00ff" alink="#ff0000"><div id="container"> <script id="js" type="text/javascript" language="JavaScript" src="../../../../doc/js/flipmenu/flipmenu.js"></script><script id="js2" type="text/javascript" src="../../../../doc/js/erlresolvelinks.js"></script><script language="JavaScript" type="text/javascript"> <!-- function getWinHeight() { var myHeight = 0; if( typeof( window.innerHeight ) == 'number' ) { //Non-IE myHeight = window.innerHeight; } else if( document.documentElement && ( document.documentElement.clientWidth || document.documentElement.clientHeight ) ) { //IE 6+ in 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Programming with Mnesia</a></li> </ul> </li> <li id="no" title="Mnesia System Information" expanded="false">Mnesia System Information<ul> <li><a href="Mnesia_chap7.html"> Top of chapter </a></li> <li title="Database Configuration Data"><a href="Mnesia_chap7.html#id2276572">Database Configuration Data</a></li> <li title="Core Dumps"><a href="Mnesia_chap7.html#id2276614">Core Dumps</a></li> <li title="Dumping Tables"><a href="Mnesia_chap7.html#id2276638">Dumping Tables</a></li> <li title="Checkpoints"><a href="Mnesia_chap7.html#id2276678">Checkpoints</a></li> <li title="Files"><a href="Mnesia_chap7.html#id2276957">Files</a></li> <li title="Loading of Tables at Start-up"><a href="Mnesia_chap7.html#id2277368">Loading of Tables at Start-up</a></li> <li title="Recovery from Communication Failure"><a href="Mnesia_chap7.html#id2277560">Recovery from Communication Failure</a></li> <li title="Recovery of Transactions"><a href="Mnesia_chap7.html#id2277693">Recovery of Transactions</a></li> <li title="Backup, Fallback, and Disaster Recovery"><a href="Mnesia_chap7.html#id2277864">Backup, Fallback, and Disaster Recovery</a></li> </ul> </li> <li id="no" title="Combining Mnesia with SNMP" expanded="false">Combining Mnesia with SNMP<ul> <li><a href="Mnesia_chap8.html"> Top of chapter </a></li> <li title="Combining Mnesia and SNMP "><a href="Mnesia_chap8.html#id2278809">Combining Mnesia and SNMP </a></li> </ul> </li> <li id="no" title="Appendix A: Mnesia Error Messages" expanded="false">Appendix A: Mnesia Error Messages<ul> <li><a href="Mnesia_App_A.html"> Top of chapter </a></li> <li title="Errors in Mnesia"><a href="Mnesia_App_A.html#id2278969">Errors in Mnesia</a></li> </ul> </li> <li id="loadscrollpos" title="Appendix B: The Backup Call Back Interface" expanded="true">Appendix B: The Backup Call Back Interface<ul> <li><a href="Mnesia_App_B.html"> Top of chapter </a></li> <li title="mnesia_backup callback behavior"><a href="Mnesia_App_B.html#id2279207">mnesia_backup callback behavior</a></li> </ul> </li> <li id="no" title="Appendix C: The Activity Access Call Back Interface" expanded="false">Appendix C: The Activity Access Call Back Interface<ul> <li><a href="Mnesia_App_C.html"> Top of chapter </a></li> <li title="mnesia_access callback behavior"><a href="Mnesia_App_C.html#id2279378">mnesia_access callback behavior</a></li> </ul> </li> <li id="no" title="Appendix D: The Fragmented Table Hashing Call Back Interface" expanded="false">Appendix D: The Fragmented Table Hashing Call Back Interface<ul> <li><a href="Mnesia_App_D.html"> Top of chapter </a></li> <li title="mnesia_frag_hash callback behavior"><a href="Mnesia_App_D.html#id2279587">mnesia_frag_hash callback behavior</a></li> </ul> </li> </ul> </div></div> <div id="content"> <div class="innertube"> <h1>9 Appendix B: The Backup Call Back Interface</h1> <h3><a name="id2279207">9.1 mnesia_backup callback behavior</a></h3> <p></p> <div class="example"><pre> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %% %% This module contains one implementation of callback functions %% used by Mnesia at backup and restore. The user may however %% write an own module the same interface as mnesia_backup and %% configure Mnesia so the alternate module performs the actual %% accesses to the backup media. This means that the user may put %% the backup on medias that Mnesia does not know about, possibly %% on hosts where Erlang is not running. %% %% The OpaqueData argument is never interpreted by other parts of %% Mnesia. It is the property of this module. Alternate implementations %% of this module may have different interpretations of OpaqueData. %% The OpaqueData argument given to open_write/1 and open_read/1 %% are forwarded directly from the user. %% %% All functions must return {ok, NewOpaqueData} or {error, Reason}. %% %% The NewOpaqueData arguments returned by backup callback functions will %% be given as input when the next backup callback function is invoked. %% If any return value does not match {ok, _} the backup will be aborted. %% %% The NewOpaqueData arguments returned by restore callback functions will %% be given as input when the next restore callback function is invoked %% If any return value does not match {ok, _} the restore will be aborted. %% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -module(mnesia_backup). -include_lib("kernel/include/file.hrl"). -export([ %% Write access open_write/1, write/2, commit_write/1, abort_write/1, %% Read access open_read/1, read/1, close_read/1 ]). %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %% Backup callback interface -record(backup, {tmp_file, file, file_desc}). %% Opens backup media for write %% %% Returns {ok, OpaqueData} or {error, Reason} open_write(OpaqueData) -> File = OpaqueData, Tmp = lists:concat([File,".BUPTMP"]), file:delete(Tmp), file:delete(File), case disk_log:open([{name, make_ref()}, {file, Tmp}, {repair, false}, {linkto, self()}]) of {ok, Fd} -> {ok, #backup{tmp_file = Tmp, file = File, file_desc = Fd}}; {error, Reason} -> {error, Reason} end. %% Writes BackupItems to the backup media %% %% Returns {ok, OpaqueData} or {error, Reason} write(OpaqueData, BackupItems) -> B = OpaqueData, case disk_log:log_terms(B#backup.file_desc, BackupItems) of ok -> {ok, B}; {error, Reason} -> abort_write(B), {error, Reason} end. %% Closes the backup media after a successful backup %% %% Returns {ok, ReturnValueToUser} or {error, Reason} commit_write(OpaqueData) -> B = OpaqueData, case disk_log:sync(B#backup.file_desc) of ok -> case disk_log:close(B#backup.file_desc) of ok -> case file:rename(B#backup.tmp_file, B#backup.file) of ok -> {ok, B#backup.file}; {error, Reason} -> {error, Reason} end; {error, Reason} -> {error, Reason} end; {error, Reason} -> {error, Reason} end. %% Closes the backup media after an interrupted backup %% %% Returns {ok, ReturnValueToUser} or {error, Reason} abort_write(BackupRef) -> Res = disk_log:close(BackupRef#backup.file_desc), file:delete(BackupRef#backup.tmp_file), case Res of ok -> {ok, BackupRef#backup.file}; {error, Reason} -> {error, Reason} end. %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %% Restore callback interface -record(restore, {file, file_desc, cont}). %% Opens backup media for read %% %% Returns {ok, OpaqueData} or {error, Reason} open_read(OpaqueData) -> File = OpaqueData, case file:read_file_info(File) of {error, Reason} -> {error, Reason}; _FileInfo -> %% file exists case disk_log:open([{file, File}, {name, make_ref()}, {repair, false}, {mode, read_only}, {linkto, self()}]) of {ok, Fd} -> {ok, #restore{file = File, file_desc = Fd, cont = start}}; {repaired, Fd, _, {badbytes, 0}} -> {ok, #restore{file = File, file_desc = Fd, cont = start}}; {repaired, Fd, _, _} -> {ok, #restore{file = File, file_desc = Fd, cont = start}}; {error, Reason} -> {error, Reason} end end. %% Reads BackupItems from the backup media %% %% Returns {ok, OpaqueData, BackupItems} or {error, Reason} %% %% BackupItems == [] is interpreted as eof read(OpaqueData) -> R = OpaqueData, Fd = R#restore.file_desc, case disk_log:chunk(Fd, R#restore.cont) of {error, Reason} -> {error, {"Possibly truncated", Reason}}; eof -> {ok, R, []}; {Cont, []} -> read(R#restore{cont = Cont}); {Cont, BackupItems, _BadBytes} -> {ok, R#restore{cont = Cont}, BackupItems}; {Cont, BackupItems} -> {ok, R#restore{cont = Cont}, BackupItems} end. %% Closes the backup media after restore %% %% Returns {ok, ReturnValueToUser} or {error, Reason} close_read(OpaqueData) -> R = OpaqueData, case disk_log:close(R#restore.file_desc) of ok -> {ok, R#restore.file}; {error, Reason} -> {error, Reason} end.</pre></div> </div> <div class="footer"> <hr> <p>Copyright © 1997-2010 Ericsson AB. 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