btrfs-progs: tests: add test for send -p on 2 mont points

Add testcase from issue, use reproducer from Axel Burri.

Issue: #96
Signed-off-by: David Sterba <dsterba@suse.com>

tests/misc-tests/029-send-p-different-mountpoints/test.sh

@@ -0,0 +1,51 @@
+#!/bin/bash
+# test that send -p does not corrupt paths when send is using 2 different mount
+# points
+
+source "$TOP/tests/common"
+
+check_prereq btrfs
+check_prereq mkfs.btrfs
+
+setup_root_helper
+prepare_test_dev
+
+# we need two mount points, cannot nest the subvoolume under TEST_MNT
+SUBVOL_MNT="$TEST_MNT/subvol"
+TOPLEVEL_MNT="$TEST_MNT/toplevel"
+TEST_MNT="$TOPLEVEL_MNT"
+mkdir -p "$TOPLEVEL_MNT" "$SUBVOL_MNT"
+
+run_check $SUDO_HELPER "$TOP/mkfs.btrfs" -f "$TEST_DEV"
+run_check_mount_test_dev
+
+run_check $SUDO_HELPER "$TOP/btrfs" subvolume create "$TOPLEVEL_MNT/subv1"
+run_check $SUDO_HELPER mount -t btrfs -o subvol=subv1 "$TEST_DEV" "$SUBVOL_MNT"
+
+run_check $SUDO_HELPER "$TOP/btrfs" subvolume create "$TOPLEVEL_MNT/test-subvol"
+run_check $SUDO_HELPER "$TOP/btrfs" subvolume snapshot -r \
+	"$TOPLEVEL_MNT/test-subvol" "$SUBVOL_MNT/test-subvol-mnt-subvol"
+run_check $SUDO_HELPER "$TOP/btrfs" subvolume snapshot -r \
+	"$TOPLEVEL_MNT/test-subvol" "$TOPLEVEL_MNT/test-subvol-mnt-root"
+
+run_mustfail_stdout "send -p on 2 mount points" \
+	$SUDO_HELPER "$TOP/btrfs" send -f /dev/null -p \
+	"$SUBVOL_MNT/test-subvol-mnt-subvol" "$TOPLEVEL_MNT/test-subvol-mnt-root" \
+	| tee -a "$RESULTS" \
+	| grep -q "not on mount point.*/toplevel" \
+	|| _fail "expected output not found, please check the logs"
+
+# without a fix, this leads to a corrupted path, with something like:
+#
+# ERROR: open st-subvol-mnt-subvol failed. No such file or directory
+#             ^^^^^^^^^^^^^^^^^^^^
+# ERROR: could not resolve rootid for .../tests/mnt/subvol/test-subvol-mnt-subvol
+
+# expected output:
+# ERROR: not on mount point: .../tests/mnt/toplevel
+
+run_check_umount_test_dev "$SUBVOL_MNT"
+run_check_umount_test_dev "$TOPLEVEL_MNT"
+
+rmdir "$SUBVOL_MNT"
+rmdir "$TOPLEVEL_MNT"