engines: Add Network Block Device (NBD) support using libnbd.

This commit adds a new engine for testing Network Block Devices
directly.  It requires libnbd (https://github.com/libguestfs/libnbd).

To see how to test nbdkit or qemu-nbd read examples/nbd.fio.

Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

HOWTO

@@ -1998,6 +1998,8 @@ I/O engine
 			requests for IME. FIO will then decide when to commit these requests.
 		**libiscsi**
 			Read and write iscsi lun with libiscsi.
+		**nbd**
+			Synchronous read and write a Network Block Device (NBD).
 
 I/O engine specific parameters
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Makefile

@@ -65,6 +65,12 @@ ifdef CONFIG_LIBISCSI
   SOURCE += engines/libiscsi.c
 endif
 
+ifdef CONFIG_LIBNBD
+  CFLAGS += $(LIBNBD_CFLAGS)
+  LIBS += $(LIBNBD_LIBS)
+  SOURCE += engines/nbd.c
+endif
+
 ifdef CONFIG_64BIT
   CFLAGS += -DBITS_PER_LONG=64
 endif

configure

@@ -149,6 +149,7 @@ disable_pmem="no"
 disable_native="no"
 march_set="no"
 libiscsi="no"
+libnbd="no"
 prefix=/usr/local
 
 # parse options
@@ -207,6 +208,8 @@ for opt do
   ;;
   --enable-libiscsi) libiscsi="yes"
   ;;
+  --enable-libnbd) libnbd="yes"
+  ;;
   --disable-tcmalloc) disable_tcmalloc="yes"
   ;;
   --help)
@@ -245,6 +248,7 @@ if test "$show_help" = "yes" ; then
   echo "--disable-native        Don't build for native host"
   echo "--with-ime=             Install path for DDN's Infinite Memory Engine"
   echo "--enable-libiscsi       Enable iscsi support"
+  echo "--enable-libnbd         Enable libnbd (NBD engine) support"
   echo "--disable-tcmalloc	Disable tcmalloc support"
   exit $exit_val
 fi
@@ -2014,6 +2018,23 @@ if test "$libiscsi" = "yes" ; then
 fi
 print_config "iscsi engine" "$libiscsi"
 
+##########################################
+# Check if we have libnbd (for NBD support).
+minimum_libnbd=0.9.6
+if test "$libnbd" = "yes" ; then
+  if $(pkg-config --atleast-version=$minimum_libnbd libnbd); then
+    libnbd="yes"
+    libnbd_cflags=$(pkg-config --cflags libnbd)
+    libnbd_libs=$(pkg-config --libs libnbd)
+  else
+    if test "$libnbd" = "yes" ; then
+      echo "libnbd" "Install libnbd >= $minimum_libnbd"
+    fi
+    libnbd="no"
+  fi
+fi
+print_config "NBD engine" "$libnbd"
+
 ##########################################
 # Check if we have lex/yacc available
 yacc="no"
@@ -2698,6 +2719,12 @@ if test "$libiscsi" = "yes" ; then
   echo "LIBISCSI_CFLAGS=$libiscsi_cflags" >> $config_host_mak
   echo "LIBISCSI_LIBS=$libiscsi_libs" >> $config_host_mak
 fi
+if test "$libnbd" = "yes" ; then
+  output_sym "CONFIG_LIBNBD"
+  echo "CONFIG_LIBNBD=m" >> $config_host_mak
+  echo "LIBNBD_CFLAGS=$libnbd_cflags" >> $config_host_mak
+  echo "LIBNBD_LIBS=$libnbd_libs" >> $config_host_mak
+fi
 cat > $TMPC << EOF
 int main(int argc, char **argv)
 {