Document use_lvmetad and global_filter in lvm.conf.5.

man/lvm.conf.5.in

@@ -104,6 +104,12 @@ otherwise it is accepted.  As an example, to ignore /dev/cdrom you could use:
 .br
 \fBdevices { filter=["r|cdrom|"] }\fP
 .IP
+\fBglobal_filter\fP \(em Since "filter" is often overriden from command line, it
+is not suitable for system-wide device filtering (udev rules, lvmetad). To hide
+devices from LVM-specific udev processing and/or from lvmetad, you need to set
+global_filter. The syntax is the same as for normal "filter" above. Devices that
+fail the global_filter are not even opened by LVM.
+.IP
 \fBcache_dir\fP \(em Persistent filter cache file directory.
 Defaults to "#DEFAULT_CACHE_DIR#".
 .IP
@@ -354,6 +360,18 @@ if \fBlocking_type\fP is set to 1.  The default is \fB/var/lock/lvm\fP.
 library to load if \fBlocking_type\fP is set to 2.
 The default is \fBliblvm2clusterlock.so\fP.  If you need to write
 such a library, look at the lib/locking source code directory.
+.IP
+\fBuse_lvmetad\fP \(em Whether to use (trust) a running instance of lvmetad. If
+this is set to 0, all commands fall back to the usual scanning mechanisms. When
+set to 1 \fBand\fP when lvmetad is running (it is not auto-started), the volume
+group metadata and PV state flags are obtained from the lvmetad instance and no
+scanning is done by the individual commands. In a setup with lvmetad, lvmetad
+udev rules \fBmust\fP be set up for LVM to work correctly. Without proper udev
+rules, all changes in block device configuration will be \fBignored\fP until a
+manual 'pvscan --cache' is performed.
+.br
+If lvmetad has been running while use_lvmetad was 0, it \fBMUST\fP be stopped before
+changing use_lvmetad to 1 and started again afterwards.
 .TP
 \fBtags\fP \(em Host tag settings
 .IP