add overflow snapshot test

The test is similar to 2000-stretch.sh, but does not create a device
loop. The disk on which the root system is mounted is used.

tests/2100-overflow.sh

@@ -0,0 +1,92 @@
+#!/bin/bash -e
+#
+# SPDX-License-Identifier: GPL-2.0+
+
+if [ -z $1 ]
+then
+	DIFF_STORAGE_DIR="/dev/shm"
+else
+	DIFF_STORAGE_DIR=$1
+fi
+DIFF_STORAGE="${DIFF_STORAGE_DIR}/diff_storage"
+
+. ./functions.sh
+. ./blksnap.sh
+
+echo "---"
+echo "Overflow snapshot test"
+
+# diff_storage_minimum=262144 - set 256 K sectors, it's 128MiB diff_storage portion size
+blksnap_load "diff_storage_minimum=262144"
+
+# check module is ready
+blksnap_version
+
+TESTDIR=/root/blksnap-test
+MPDIR=/mnt/blksnap-test
+
+mkdir -p ${TESTDIR}
+rm -rf ${TESTDIR}/*
+mkdir -p ${MPDIR}
+rm -rf ${MPDIR}*/
+
+MPTESTDIR=$(stat -c %m ${TESTDIR})
+DEVICE="/dev/block/"$(mountpoint -d ${MPTESTDIR})
+
+generate_files_direct ${TESTDIR} "before" 5
+drop_cache
+
+rm -f ${DIFF_STORAGE}
+fallocate --length 128MiB ${DIFF_STORAGE}
+blksnap_snapshot_create "${DEVICE}" "${DIFF_STORAGE}" "512M"
+
+generate_files_direct ${TESTDIR} "tracked" 5
+drop_cache
+
+blksnap_snapshot_watcher
+#echo "Press for taking snapshot..."
+#read -n 1
+
+blksnap_snapshot_take
+
+generate_block_MB ${TESTDIR} "after" 100
+check_files ${TESTDIR}
+
+echo "Check snapshot before overflow."
+#echo "press..."
+#read -n 1
+
+DEVICE_IMAGE=$(blksnap_get_image ${DEVICE})
+IMAGE=${MPDIR}/image0
+mkdir -p ${IMAGE}
+mount ${DEVICE_IMAGE} ${IMAGE}
+check_files ${IMAGE}/${TESTDIR}
+
+echo "Try to make snapshot overflow."
+#echo "press..."
+#read -n 1
+generate_block_MB ${TESTDIR} "overflow" 768
+
+echo "Umount images"
+umount ${IMAGE}
+
+echo "Destroy snapshot"
+#echo "press..."
+#read -n 1
+
+blksnap_snapshot_destroy
+
+#echo "Check generated data"
+#check_files ${TESTDIR}
+
+blksnap_watcher_wait
+
+blksnap_detach ${DEVICE}
+
+blksnap_unload
+
+echo "Cleanup test directory" ${TESTDIR}
+rm -rf ${TESTDIR}/*
+
+echo "Overflow snapshot test finish"
+echo "---"