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>

configure

@@ -290,6 +290,7 @@ netmap="no"
 sdl=""
 sdlabi=""
 virtfs=""
+mpath=""
 vnc="yes"
 sparse="no"
 vde=""
@@ -936,6 +937,10 @@ for opt do
   ;;
   --enable-virtfs) virtfs="yes"
   ;;
+  --disable-mpath) mpath="no"
+  ;;
+  --enable-mpath) mpath="yes"
+  ;;
   --disable-vnc) vnc="no"
   ;;
   --enable-vnc) vnc="yes"
@@ -1479,6 +1484,7 @@ disabled with --disable-FEATURE, default is enabled if available:
   vnc-png         PNG compression for VNC server
   cocoa           Cocoa UI (Mac OS X only)
   virtfs          VirtFS
+  mpath           Multipath persistent reservation passthrough
   xen             xen backend driver support
   xen-pci-passthrough
   brlapi          BrlAPI (Braile)
@@ -3299,6 +3305,30 @@ else
       "Please install the pixman devel package."
 fi
 
+##########################################
+# libmpathpersist probe
+
+if test "$mpath" != "no" ; then
+  cat > $TMPC <<EOF
+#include <libudev.h>
+#include <mpath_persist.h>
+unsigned mpath_mx_alloc_len = 1024;
+int logsink;
+int main(void) {
+    struct udev *udev = udev_new();
+    mpath_lib_init(udev);
+    return 0;
+}
+EOF
+  if compile_prog "" "-ludev -lmultipath -lmpathpersist" ; then
+    mpathpersist=yes
+  else
+    mpathpersist=no
+  fi
+else
+  mpathpersist=no
+fi
+
 ##########################################
 # libcap probe
 
@@ -5044,12 +5074,24 @@ if test "$softmmu" = yes ; then
       fi
       virtfs=no
     fi
+    if test "$mpath" != no && test "$mpathpersist" = yes ; then
+      mpath=yes
+    else
+      if test "$mpath" = yes; then
+        error_exit "Multipath requires libmpathpersist devel"
+      fi
+      mpath=no
+    fi
     tools="$tools scsi/qemu-pr-helper\$(EXESUF)"
   else
     if test "$virtfs" = yes; then
       error_exit "VirtFS is supported only on Linux"
     fi
     virtfs=no
+    if test "$mpath" = yes; then
+      error_exit "Multipath is supported only on Linux"
+    fi
+    mpath=no
   fi
 fi
 
@@ -5295,6 +5337,7 @@ echo "Audio drivers     $audio_drv_list"
 echo "Block whitelist (rw) $block_drv_rw_whitelist"
 echo "Block whitelist (ro) $block_drv_ro_whitelist"
 echo "VirtFS support    $virtfs"
+echo "Multipath support $mpath"
 echo "VNC support       $vnc"
 if test "$vnc" = "yes" ; then
     echo "VNC SASL support  $vnc_sasl"
@@ -5738,6 +5781,9 @@ fi
 if test "$virtfs" = "yes" ; then
   echo "CONFIG_VIRTFS=y" >> $config_host_mak
 fi
+if test "$mpath" = "yes" ; then
+  echo "CONFIG_MPATH=y" >> $config_host_mak
+fi
 if test "$vhost_scsi" = "yes" ; then
   echo "CONFIG_VHOST_SCSI=y" >> $config_host_mak
 fi