Configurable block format whitelist

We have code for a quite a few block formats.  While I trust that all
of these formats are useful at least for some people in some
circumstances, some of them are of a kind that friends don't let
friends use in production.

This patch provides an optional block format whitelist, default off.
If a whitelist is configured with --block-drv-whitelist, QEMU proper
can use only whitelisted formats.  Other programs, like qemu-img, are
not affected.

Drivers for formats off the whitelist still participate in format
probing, to ensure all programs probe exactly the same.  Without that,
QEMU proper would be prone to treat images with a format off the
whitelist as raw when the image's format is probed.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

configure

@@ -38,6 +38,7 @@ cc="gcc"
 audio_drv_list=""
 audio_card_list="ac97 es1370 sb16"
 audio_possible_cards="ac97 es1370 sb16 cs4231a adlib gus"
+block_drv_whitelist=""
 host_cc="gcc"
 ar="ar"
 make="make"
@@ -430,6 +431,8 @@ for opt do
   ;;
   --audio-drv-list=*) audio_drv_list="$optarg"
   ;;
+  --block-drv-whitelist=*) block_drv_whitelist=`echo "$optarg" | sed -e 's/,/ /g'`
+  ;;
   --enable-debug-tcg) debug_tcg="yes"
   ;;
   --disable-debug-tcg) debug_tcg="no"
@@ -661,6 +664,8 @@ echo "  --audio-drv-list=LIST    set audio drivers list:"
 echo "                           Available drivers: $audio_possible_drivers"
 echo "  --audio-card-list=LIST   set list of emulated audio cards [$audio_card_list]"
 echo "                           Available cards: $audio_possible_cards"
+echo "  --block-drv-whitelist=L  set block driver whitelist"
+echo "                           (affects only QEMU, not qemu-img)"
 echo "  --enable-mixemu          enable mixer emulation"
 echo "  --disable-xen            disable xen backend driver support"
 echo "  --enable-xen             enable xen backend driver support"
@@ -1826,6 +1831,7 @@ echo "check support     $check_utests"
 echo "mingw32 support   $mingw32"
 echo "Audio drivers     $audio_drv_list"
 echo "Extra audio cards $audio_card_list"
+echo "Block whitelist   $block_drv_whitelist"
 echo "Mixer emulation   $mixemu"
 echo "VNC TLS support   $vnc_tls"
 echo "VNC SASL support  $vnc_sasl"
@@ -1948,6 +1954,7 @@ fi
 if test "$audio_win_int" = "yes" ; then
   echo "CONFIG_AUDIO_WIN_INT=y" >> $config_host_mak
 fi
+echo "CONFIG_BDRV_WHITELIST=$block_drv_whitelist" >> $config_host_mak
 if test "$mixemu" = "yes" ; then
   echo "CONFIG_MIXEMU=y" >> $config_host_mak
 fi