Without conv=notrunc, dd will automatically truncate the output file to
the @seek value at least.  We want to test post-EOF I/O, not truncate,
so pass conv=notrunc.

(It does not make a difference in practice because we only seek to the
EOF, so the truncate effectively does nothing, but this is still
cleaner.)

Signed-off-by: Hanna Czenczek <hreitz@redhat.com>
---
 tests/qemu-iotests/308 | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/tests/qemu-iotests/308 b/tests/qemu-iotests/308
index 033d5cbe22..6ecb275555 100755
--- a/tests/qemu-iotests/308
+++ b/tests/qemu-iotests/308
@@ -296,7 +296,8 @@ orig_disk_usage=$(disk_usage "$TEST_IMG")
 # Should fail (exports are non-growable by default)
 # (Note that qemu-io can never write beyond the EOF, so we have to use
 # dd here)
-dd if=/dev/zero of="$EXT_MP" bs=1 count=64k seek=$orig_len 2>&1 \
+dd if=/dev/zero of="$EXT_MP" bs=1 count=64k seek=$orig_len \
+    conv=notrunc 2>&1 \
     | _filter_testdir | _filter_imgfmt
 
 echo
@@ -333,7 +334,7 @@ fuse_export_add \
     'node-protocol'
 
 # Now we should be able to write beyond the EOF
-dd if=/dev/zero of="$EXT_MP" bs=1 count=64k seek=$new_len 2>&1 \
+dd if=/dev/zero of="$EXT_MP" bs=1 count=64k seek=$new_len conv=notrunc 2>&1 \
     | _filter_testdir | _filter_imgfmt
 
 new_len=$(get_proto_len "$EXT_MP" "$TEST_IMG")
-- 
2.53.0