iotests: Do not pipe _make_test_img

Executing _make_test_img as part of a pipe will undo all variable
changes it has done.  As such, this could not work with FUSE (because
we want to remember all of our exports and their qemu instances).

Replace the pipe by a temporary file in 071 and 174 (the two tests that
can run on FUSE).

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20201027190600.192171-9-mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

tests/qemu-iotests/071

@@ -61,8 +61,17 @@ echo
 echo "=== Testing blkverify through filename ==="
 echo
 
-TEST_IMG="$TEST_IMG.base" IMGFMT="raw" _make_test_img --no-opts $IMG_SIZE |\
-    _filter_imgfmt
+# _make_test_img may set variables that we need to retain.  Everything
+# in a pipe is executed in a subshell, so doing so would throw away
+# all changes.  Therefore, we have to store the output in some temp
+# file and filter that.
+scratch_out="$TEST_DIR/img-create.out"
+
+TEST_IMG="$TEST_IMG.base" IMGFMT="raw" _make_test_img --no-opts $IMG_SIZE \
+    >"$scratch_out"
+_filter_imgfmt <"$scratch_out"
+rm -f "$scratch_out"
+
 _make_test_img $IMG_SIZE
 $QEMU_IO -c "open -o driver=raw,file.driver=blkverify,file.raw.filename=$TEST_IMG.base $TEST_IMG" \
          -c 'read 0 512' -c 'write -P 42 0x38000 512' -c 'read -P 42 0x38000 512' | _filter_qemu_io
@@ -76,8 +85,10 @@ echo
 echo "=== Testing blkverify through file blockref ==="
 echo
 
-TEST_IMG="$TEST_IMG.base" IMGFMT="raw" _make_test_img --no-opts $IMG_SIZE |\
-    _filter_imgfmt
+TEST_IMG="$TEST_IMG.base" IMGFMT="raw" _make_test_img --no-opts $IMG_SIZE \
+    >"$scratch_out"
+_filter_imgfmt <"$scratch_out"
+
 _make_test_img $IMG_SIZE
 $QEMU_IO -c "open -o driver=raw,file.driver=blkverify,file.raw.filename=$TEST_IMG.base,file.test.driver=$IMGFMT,file.test.file.filename=$TEST_IMG" \
          -c 'read 0 512' -c 'write -P 42 0x38000 512' -c 'read -P 42 0x38000 512' | _filter_qemu_io

tests/qemu-iotests/174

@@ -40,7 +40,15 @@ _unsupported_fmt raw
 
 
 size=256K
-IMGFMT=raw IMGKEYSECRET= _make_test_img --no-opts $size | _filter_imgfmt
+
+# _make_test_img may set variables that we need to retain.  Everything
+# in a pipe is executed in a subshell, so doing so would throw away
+# all changes.  Therefore, we have to store the output in some temp
+# file and filter that.
+scratch_out="$TEST_DIR/img-create.out"
+IMGFMT=raw IMGKEYSECRET= _make_test_img --no-opts $size >"$scratch_out"
+_filter_imgfmt <"$scratch_out"
+rm -f "$scratch_out"
 
 echo
 echo "== reading wrong format should fail =="