btrfs-progs: convert-test: Add test case for discontinuous hole extent

For ext* fs containing a large hole(larger than 128M), btrfs-convert
will only insert one 128M hole extent and skip the remaining.

This leads to discontinuous file extents.

Add test case for it, and since it's a pinpoint regression test case, no
combination of convert options nor checksum verification.

Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>

tests/convert-tests/006-large-hole-extent/test.sh

@@ -0,0 +1,23 @@
+#!/bin/bash
+# Create a base image with large hole extent, then convert to btrfs,
+# check the converted image.
+# Check if btrfs-convert can handle such large hole.
+# Fast pinpoint regression test. No options combination nor checksum
+# verification
+
+source $TOP/tests/common
+source $TOP/tests/common.convert
+
+setup_root_helper
+prepare_test_dev 512M
+check_prereq btrfs-convert
+
+default_mke2fs="mke2fs -t ext4 -b 4096"
+convert_test_preamble '' 'large hole extent test' 16k "$default_mke2fs"
+convert_test_prep_fs $default_mke2fs
+
+run_check $SUDO_HELPER dd if=/dev/zero of=$TEST_MNT/file bs=1M \
+	count=1 seek=1024 > /dev/null 2>&1
+
+run_check_umount_test_dev
+convert_test_do_convert