btrfs-progs: tests: Add test for super block recovery

This functionality regressed some time ago and it was never caught. Seems no
one complained of that, but to be sure add a regression test to prevent future
regressions.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

tests/fsck-tests/029-superblock-recovery/test.sh

@@ -0,0 +1,64 @@
+#!/bin/bash
+# Test that any superblock is correctly detected
+# and fixed by btrfs rescue
+
+source "$TOP/tests/common"
+
+check_prereq btrfs
+check_prereq mkfs.btrfs
+check_prereq btrfs-select-super
+
+setup_root_helper
+
+rm -f dev1
+run_check truncate -s 260G dev1
+loop=$(run_check_stdout $SUDO_HELPER losetup --find --show dev1)
+
+# Create the test file system.
+run_check $SUDO_HELPER "$TOP"/mkfs.btrfs -f "$loop"
+
+function check_corruption {
+	local sb_offset=$1
+	local source_sb=$2
+
+
+	# First we ensure we can mount it successfully
+	run_check $SUDO_HELPER mount $loop "$TEST_MNT"
+	run_check $SUDO_HELPER umount "$TEST_MNT"
+
+	# Now corrupt 1k of the superblock at sb_offset
+	run_check $SUDO_HELPER dd bs=1K count=1 seek=$(($sb_offset + 1)) if=/dev/zero of="$loop"
+
+	#if corrupting one of the sb copies, copy it over the initial superblock
+	if [ ! -z $source_sb ]; then
+		local shift_val=$((16 << $source_sb * 12 ))
+		run_check $SUDO_HELPER dd bs=1K count=4 seek=64 skip=$shift_val if="$loop" of="$loop"
+	fi
+
+	run_mustfail "Mounted fs with corrupted superblock" \
+		$SUDO_HELPER mount $loop "$TEST_MNT"
+
+	# Now run btrfs rescue which should fix the superblock. It uses 2
+	# to signal success of recovery use mayfail to ignore that retval
+	# but still log the output of the command
+	run_mayfail $SUDO_HELPER "$TOP"/btrfs rescue super-recover -yv "$loop"
+	if [ $? != 2 ]; then
+		_fail "couldn't rescue super"
+	fi
+
+	run_check $SUDO_HELPER mount $loop "$TEST_MNT"
+	run_check $SUDO_HELPER umount "$TEST_MNT"
+}
+
+_log "Corrupting first superblock"
+check_corruption 64
+
+_log "Corrupting second superblock"
+check_corruption 65536 1
+
+_log "Corrupting third superblock"
+check_corruption 268435456 2
+
+# Cleanup
+run_check $SUDO_HELPER losetup -d "$loop"
+rm -f dev1