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Add server support for "plugin" libraries that can be used for add-on tasks
such as debugging and performance measurement. This consists of two features: a table of "rendezvous variables" that allows separately-loaded shared libraries to communicate, and a new GUC setting "local_preload_libraries" that allows libraries to be loaded into specific sessions without explicit cooperation from the client application. To make local_preload_libraries as flexible as possible, we do not restrict its use to superusers; instead, it is restricted to load only libraries stored in $libdir/plugins/. The existing LOAD command has also been modified to allow non-superusers to LOAD libraries stored in this directory. This patch also renames the existing GUC variable preload_libraries to shared_preload_libraries (after a suggestion by Simon Riggs) and does some code refactoring in dfmgr.c to improve clarity. Korry Douglas, with a little help from Tom Lane.
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‎doc/src/sgml/config.sgml

Lines changed: 59 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -1,4 +1,4 @@
1-
<!-- $PostgreSQL: pgsql/doc/src/sgml/config.sgml,v 1.73 2006/08/08 19:15:07 tgl Exp $ -->
1+
<!-- $PostgreSQL: pgsql/doc/src/sgml/config.sgml,v 1.74 2006/08/15 18:26:58 tgl Exp $ -->
22

33
<chapter Id="runtime-config">
44
<title>Server Configuration</title>
@@ -949,10 +949,10 @@ SET ENABLE_SEQSCAN TO OFF;
949949
</listitem>
950950
</varlistentry>
951951

952-
<varlistentry id="guc-preload-libraries" xreflabel="preload_libraries">
953-
<term><varname>preload_libraries</varname> (<type>string</type>)</term>
952+
<varlistentry id="guc-shared-preload-libraries" xreflabel="shared_preload_libraries">
953+
<term><varname>shared_preload_libraries</varname> (<type>string</type>)</term>
954954
<indexterm>
955-
<primary><varname>preload_libraries</> configuration parameter</primary>
955+
<primary><varname>shared_preload_libraries</> configuration parameter</primary>
956956
</indexterm>
957957
<listitem>
958958
<para>
@@ -963,6 +963,7 @@ SET ENABLE_SEQSCAN TO OFF;
963963
<literal>mylib.so</> (or on some platforms,
964964
<literal>mylib.sl</>) to be preloaded from the installation's
965965
standard library directory.
966+
This parameter can only be set at server start.
966967
</para>
967968

968969
<para>
@@ -3642,6 +3643,60 @@ dynamic_library_path = 'C:\tools\postgresql;H:\my_project\lib;$libdir'
36423643
</para>
36433644
</listitem>
36443645
</varlistentry>
3646+
3647+
<varlistentry id="guc-local-preload-libraries" xreflabel="local_preload_libraries">
3648+
<term><varname>local_preload_libraries</varname> (<type>string</type>)</term>
3649+
<indexterm>
3650+
<primary><varname>local_preload_libraries</> configuration parameter</primary>
3651+
</indexterm>
3652+
<indexterm>
3653+
<primary><filename>$libdir/plugins</></primary>
3654+
</indexterm>
3655+
<listitem>
3656+
<para>
3657+
This variable specifies one or more shared libraries that are
3658+
to be preloaded at connection start. If more than one library
3659+
is to be loaded, separate their names with commas.
3660+
This parameter cannot be changed after the start of a particular
3661+
session.
3662+
</para>
3663+
3664+
<para>
3665+
Because this is not a superuser-only option, the libraries
3666+
that can be loaded are restricted to those appearing in the
3667+
<filename>plugins</> subdirectory of the installation's
3668+
standard library directory. (It is the database administrator's
3669+
responsibility to ensure that only <quote>safe</> libraries
3670+
are installed there.) Entries in <varname>local_preload_libraries</>
3671+
can specify this directory explicitly, for example
3672+
<literal>$libdir/plugins/mylib</literal>, or just specify
3673+
the library name &mdash; <literal>mylib</literal> would have
3674+
the same effect as <literal>$libdir/plugins/mylib</literal>.
3675+
</para>
3676+
3677+
<para>
3678+
There is no performance advantage to loading a library at session
3679+
start rather than when it is first used. Rather, the intent of
3680+
this feature is to allow debugging or performance-measurement
3681+
libraries to be loaded into specific sessions without an explicit
3682+
<command>LOAD</> command being given. For example, debugging could
3683+
be enabled for all sessions under a given user name by setting
3684+
this parameter with <command>ALTER USER SET</>.
3685+
</para>
3686+
3687+
<para>
3688+
If a specified library is not found,
3689+
the connection attempt will fail.
3690+
</para>
3691+
3692+
<para>
3693+
Every PostgreSQL-supported library has a <quote>magic
3694+
block</> that is checked to guarantee compatibility.
3695+
For this reason, non-PostgreSQL libraries cannot be
3696+
loaded in this way.
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</para>
3698+
</listitem>
3699+
</varlistentry>
36453700

36463701
</variablelist>
36473702
</sect2>

‎doc/src/sgml/ref/load.sgml

Lines changed: 14 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1,5 +1,5 @@
11
<!--
2-
$PostgreSQL: pgsql/doc/src/sgml/ref/load.sgml,v 1.21 2005/01/04 00:39:53 tgl Exp $
2+
$PostgreSQL: pgsql/doc/src/sgml/ref/load.sgml,v 1.22 2006/08/15 18:26:58 tgl Exp $
33
-->
44

55
<refentry id="SQL-LOAD">
@@ -44,6 +44,19 @@ LOAD '<replaceable class="PARAMETER">filename</replaceable>'
4444
shared library file name extension. See <xref linkend="xfunc-c"> for
4545
more information on this topic.
4646
</para>
47+
48+
<indexterm>
49+
<primary><filename>$libdir/plugins</></primary>
50+
</indexterm>
51+
52+
<para>
53+
Non-superusers may only apply <command>LOAD</> to library files
54+
located in <filename>$libdir/plugins/</> &mdash; the specified
55+
<replaceable class="PARAMETER">filename</replaceable> must begin
56+
with exactly that string. (It is the database administrator's
57+
responsibility to ensure that only <quote>safe</> libraries
58+
are installed there.)
59+
</para>
4760
</refsect1>
4861

4962
<refsect1 id="sql-load-compat">

‎src/backend/postmaster/postmaster.c

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -37,7 +37,7 @@
3737
*
3838
*
3939
* IDENTIFICATION
40-
* $PostgreSQL: pgsql/src/backend/postmaster/postmaster.c,v 1.498 2006/08/08 19:15:07 tgl Exp $
40+
* $PostgreSQL: pgsql/src/backend/postmaster/postmaster.c,v 1.499 2006/08/15 18:26:58 tgl Exp $
4141
*
4242
* NOTES
4343
*
@@ -709,7 +709,7 @@ PostmasterMain(int argc, char *argv[])
709709
/*
710710
* process any libraries that should be preloaded at postmaster start
711711
*/
712-
process_preload_libraries();
712+
process_shared_preload_libraries();
713713

714714
/*
715715
* Remove old temporary files. At this point there can be no other

‎src/backend/tcop/postgres.c

Lines changed: 7 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/backend/tcop/postgres.c,v 1.498 2006/08/13 22:18:08 tgl Exp $
11+
* $PostgreSQL: pgsql/src/backend/tcop/postgres.c,v 1.499 2006/08/15 18:26:58 tgl Exp $
1212
*
1313
* NOTES
1414
* this is the "main" module of the postgres backend and
@@ -3000,6 +3000,12 @@ PostgresMain(int argc, char *argv[], const char *username)
30003000
if (IsUnderPostmaster && Log_disconnections)
30013001
on_proc_exit(log_disconnections, 0);
30023002

3003+
/*
3004+
* process any libraries that should be preloaded at backend start
3005+
* (this likewise can't be done until GUC settings are complete)
3006+
*/
3007+
process_local_preload_libraries();
3008+
30033009
/*
30043010
* Send this backend's cancellation info to the frontend.
30053011
*/

‎src/backend/tcop/utility.c

Lines changed: 3 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -10,7 +10,7 @@
1010
*
1111
*
1212
* IDENTIFICATION
13-
* $PostgreSQL: pgsql/src/backend/tcop/utility.c,v 1.265 2006/08/12 20:05:56 tgl Exp $
13+
* $PostgreSQL: pgsql/src/backend/tcop/utility.c,v 1.266 2006/08/15 18:26:58 tgl Exp $
1414
*
1515
*-------------------------------------------------------------------------
1616
*/
@@ -886,12 +886,9 @@ ProcessUtility(Node *parsetree,
886886
{
887887
LoadStmt *stmt = (LoadStmt *) parsetree;
888888

889-
if (!superuser())
890-
ereport(ERROR,
891-
(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
892-
errmsg("must be superuser to do LOAD")));
893889
closeAllVfds(); /* probably not necessary... */
894-
load_file(stmt->filename);
890+
/* Allowed names are restricted if you're not superuser */
891+
load_file(stmt->filename, !superuser());
895892
}
896893
break;
897894

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