iotests: Switch nbd tests to use Unix rather than TCP

Up to now, all it took to cause a lot of iotest failures was to have a
background process such as 'nbdkit -p 10810 null' running, because we
hard-coded the TCP port.  Switching to a Unix socket eliminates this
contention.  We still have TCP coverage in test 233, and that test is
more careful to not pick a hard-coded port.

Add a comment explaining where the format layer applies when using
NBD as protocol (until NBD gains support for a resize extension, we
only pipe raw bytes over the wire).

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20191114213415.23499-3-eblake@redhat.com>
[eblake: Tweak socket name per Max Reitz' review]

tests/qemu-iotests/common.filter

@@ -127,7 +127,8 @@ _filter_img_create()
         -e "s#$TEST_DIR#TEST_DIR#g" \
         -e "s#$SOCK_DIR#SOCK_DIR#g" \
         -e "s#$IMGFMT#IMGFMT#g" \
-        -e 's#nbd:127.0.0.1:10810#TEST_DIR/t.IMGFMT#g' \
+        -e 's#nbd:127.0.0.1:[0-9]\\+#TEST_DIR/t.IMGFMT#g' \
+        -e 's#nbd+unix:///\??socket=SOCK_DIR/nbd#TEST_DIR/t.IMGFMT#g' \
         -e "s# encryption=off##g" \
         -e "s# cluster_size=[0-9]\\+##g" \
         -e "s# table_size=[0-9]\\+##g" \
@@ -164,7 +165,8 @@ _filter_img_info()
         -e "s#$TEST_DIR#TEST_DIR#g" \
         -e "s#$SOCK_DIR#SOCK_DIR#g" \
         -e "s#$IMGFMT#IMGFMT#g" \
-        -e 's#nbd://127.0.0.1:10810$#TEST_DIR/t.IMGFMT#g' \
+        -e 's#nbd://127.0.0.1:[0-9]\\+$#TEST_DIR/t.IMGFMT#g' \
+        -e 's#nbd+unix:///\??socket=SOCK_DIR/nbd#TEST_DIR/t.IMGFMT#g' \
         -e 's#json.*vdisk-id.*vxhs"}}#TEST_DIR/t.IMGFMT#' \
         -e "/encrypted: yes/d" \
         -e "/cluster_size: [0-9]\\+/d" \

tests/qemu-iotests/common.rc

@@ -217,7 +217,7 @@ if [ "$IMGOPTSSYNTAX" = "true" ]; then
         TEST_IMG="$DRIVER,file.filename=$TEST_DIR/t.$IMGFMT"
     elif [ "$IMGPROTO" = "nbd" ]; then
         TEST_IMG_FILE=$TEST_DIR/t.$IMGFMT
-        TEST_IMG="$DRIVER,file.driver=nbd,file.host=127.0.0.1,file.port=10810"
+        TEST_IMG="$DRIVER,file.driver=nbd,file.type=unix,file.path=$SOCKDIR/nbd"
     elif [ "$IMGPROTO" = "ssh" ]; then
         TEST_IMG_FILE=$TEST_DIR/t.$IMGFMT
         TEST_IMG="$DRIVER,file.driver=ssh,file.host=127.0.0.1,file.path=$TEST_IMG_FILE"
@@ -233,7 +233,7 @@ else
         TEST_IMG=$TEST_DIR/t.$IMGFMT
     elif [ "$IMGPROTO" = "nbd" ]; then
         TEST_IMG_FILE=$TEST_DIR/t.$IMGFMT
-        TEST_IMG="nbd:127.0.0.1:10810"
+        TEST_IMG="nbd+unix:///?socket=$SOCK_DIR/nbd"
     elif [ "$IMGPROTO" = "ssh" ]; then
         TEST_IMG_FILE=$TEST_DIR/t.$IMGFMT
         REMOTE_TEST_DIR="ssh://\\($USER@\\)\\?127.0.0.1\\(:[0-9]\\+\\)\\?$TEST_DIR"
@@ -293,7 +293,7 @@ _stop_nbd_server()
         local QEMU_NBD_PID
         read QEMU_NBD_PID < "${QEMU_TEST_DIR}/qemu-nbd.pid"
         kill ${QEMU_NBD_PID}
-        rm -f "${QEMU_TEST_DIR}/qemu-nbd.pid"
+        rm -f "${QEMU_TEST_DIR}/qemu-nbd.pid" "$SOCK_DIR/nbd"
     fi
 }
 
@@ -349,11 +349,14 @@ _make_test_img()
      fi
     ) | _filter_img_create
 
-    # Start an NBD server on the image file, which is what we'll be talking to
+    # Start an NBD server on the image file, which is what we'll be talking to.
+    # Once NBD gains resize support, we may also want to use -f raw at the
+    # server and interpret format over NBD, but for now, the format is
+    # interpreted at the server and raw data sent over NBD.
     if [ $IMGPROTO = "nbd" ]; then
         # Pass a sufficiently high number to -e that should be enough for all
         # tests
-        eval "$QEMU_NBD -v -t -b 127.0.0.1 -p 10810 -f $IMGFMT -e 42 -x '' $TEST_IMG_FILE >/dev/null &"
+        eval "$QEMU_NBD -v -t -k '$SOCK_DIR/nbd' -f $IMGFMT -e 42 -x '' $TEST_IMG_FILE >/dev/null &"
         sleep 1 # FIXME: qemu-nbd needs to be listening before we continue
     fi