scsi: add multipath support to qemu-pr-helper
Proper support of persistent reservation for multipath devices requires
communication with the multipath daemon, so that the reservation is
registered and applied when a path comes up. The device mapper
utilities provide a library to do so; this patch makes qemu-pr-helper.c
detect multipath devices and, when one is found, delegate the operation
to libmpathpersist.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/docs/pr-manager.rst b/docs/pr-manager.rst
index 7107e59..9b1de19 100644
--- a/docs/pr-manager.rst
+++ b/docs/pr-manager.rst
@@ -60,6 +60,7 @@
-d, --daemon run in the background
-q, --quiet decrease verbosity
+-v, --verbose increase verbosity
-f, --pidfile=path PID file when running as a daemon
-k, --socket=path path to the socket
-T, --trace=trace-opts tracing options
@@ -82,3 +83,29 @@
-u, --user=user user to drop privileges to
-g, --group=group group to drop privileges to
+
+---------------------------------------------
+Multipath devices and persistent reservations
+---------------------------------------------
+
+Proper support of persistent reservation for multipath devices requires
+communication with the multipath daemon, so that the reservation is
+registered and applied when a path is newly discovered or becomes online
+again. :command:`qemu-pr-helper` can do this if the ``libmpathpersist``
+library was available on the system at build time.
+
+As of August 2017, a reservation key must be specified in ``multipath.conf``
+for ``multipathd`` to check for persistent reservation for newly
+discovered paths or reinstated paths. The attribute can be added
+to the ``defaults`` section or the ``multipaths`` section; for example::
+
+ multipaths {
+ multipath {
+ wwid XXXXXXXXXXXXXXXX
+ alias yellow
+ reservation_key 0x123abc
+ }
+ }
+
+Linking :program:`qemu-pr-helper` to ``libmpathpersist`` does not impede
+its usage on regular SCSI devices.
