btrfs-progs: tests: add test case for basic checksum conversion

Test the following:

- Create a btrfs with crc32c csum
- Populate the filesystem
- Convert the filesystem to the following csums:
  * xxhash
  * blake2
  * sha256
  * crc32c

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

tests/misc-tests/064-csum-conversion-basic/test.sh

@@ -0,0 +1,30 @@
+#!/bin/bash
+# Verify the csum conversion works as expected.
+
+source "$TEST_TOP/common" || exit
+source "$TEST_TOP/common.convert" || exit
+
+check_experimental_build
+setup_root_helper
+prepare_test_dev
+
+convert_to_csum()
+{
+	local new_csum="$1"
+
+	run_check "$TOP/btrfstune" --csum "$new_csum" "$TEST_DEV"
+	run_check "$TOP/btrfs" check --check-data-csum "$TEST_DEV"
+}
+
+run_check_mkfs_test_dev --csum crc32c
+
+# We only mount the filesystem once to populate its contents, later one we
+# would never mount the fs (to reduce the dependency on kernel features).
+run_check_mount_test_dev
+populate_fs
+run_check_umount_test_dev
+
+convert_to_csum xxhash
+convert_to_csum blake2
+convert_to_csum sha256
+convert_to_csum crc32c