[Libguestfs] [nbdkit PATCH 3/4] truncate: Test for safe multi-connect size handling

[Eric Blake]

Test the just-fixed bug in the truncate filter. Although it is in
general unsafe to shrink an image being served by the file plugin, the
test is careful to only issue operations on connection A after the
file has been resized back to its original length, in order to prove
whether the smaller size observed during the short-lived connection B
bleeds over into the pread results seen by connection A.  If this test
is applied without the previous patch, the second read from A sees all
zeroes instead of the desired pattern 2.

Signed-off-by: Eric Blake <eblake at redhat.com>
---
 tests/Makefile.am       |  2 +
 tests/test-truncate4.sh | 85 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 87 insertions(+)
 create mode 100755 tests/test-truncate4.sh

diff --git a/tests/Makefile.am b/tests/Makefile.am
index 4b7aa22..4148793 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -122,6 +122,7 @@ EXTRA_DIST = \
 	test-truncate1.sh \
 	test-truncate2.sh \
 	test-truncate3.sh \
+	test-truncate4.sh \
 	test-truncate-extents.sh \
 	test-vddk.sh \
 	test-vddk-real.sh \
@@ -937,6 +938,7 @@ TESTS += \
 	test-truncate1.sh \
 	test-truncate2.sh \
 	test-truncate3.sh \
+	test-truncate4.sh \
 	test-truncate-extents.sh

 # xz filter test.
diff --git a/tests/test-truncate4.sh b/tests/test-truncate4.sh
new file mode 100755
index 0000000..e4be626
--- /dev/null
+++ b/tests/test-truncate4.sh
@@ -0,0 +1,85 @@
+#!/usr/bin/env bash
+# nbdkit
+# Copyright (C) 2019 Red Hat Inc.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+# * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#
+# * Redistributions in binary form must reproduce the above copyright
+# notice, this list of conditions and the following disclaimer in the
+# documentation and/or other materials provided with the distribution.
+#
+# * Neither the name of Red Hat nor the names of its contributors may be
+# used to endorse or promote products derived from this software without
+# specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND
+# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+# THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
+# PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR
+# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
+# USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+# ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+# OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+# OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+# SUCH DAMAGE.
+
+# Regression test when next_ops->get_size changes between connections.
+# For now, NBD does not support dynamic resize; but the file plugin
+# reads size from the file system for each new connection, at which
+# point the client remembers that size for the life of the connection.
+# We are testing that connection A can still see the tail of a file,
+# even when connection B is opened while the file was temporarily
+# shorter (if the actions of connection B affect the size visible
+# through connection A, we didn't isolate per-connection state).
+
+source ./functions.sh
+set -e
+set -x
+
+requires qemu-io --version
+
+sock=`mktemp -u`
+files="truncate4.out truncate4.pid $sock truncate4.data"
+rm -f $files
+cleanup_fn rm -f $files
+
+# Initial file contents: 1k of pattern 1
+truncate -s 1024 truncate4.data
+qemu-io -c 'w -P 1 0 1024' -f raw truncate4.data
+
+# Run nbdkit with file plugin and truncate filter in front.
+start_nbdkit -P truncate4.pid -U $sock \
+       --filter=truncate \
+       file truncate4.data \
+       round-up=1024
+
+fail=0
+exec 4>&1 # Save original stdout
+{
+    exec 5>&1 >&4 # Save connection A, set stdout back to original
+    echo 'Reading from connection A, try 1'
+    echo 'r -P 1 0 1024' >&5
+    sleep 1
+    echo 'Resizing down'
+    truncate -s 512 truncate4.data
+    echo 'Reading from connection B'
+    echo 'r -P 1 0 512' | qemu-io -f raw nbd:unix:$sock >> truncate4.out
+    echo 'Restoring size'
+    truncate -s 1024 truncate4.data
+    qemu-io -c 'w -P 2 0 1024' -f raw truncate4.data
+    echo 'Reading from connection A, try 2'
+    echo 'r -P 2 512 512' >&5
+    echo 'quit' >&5
+} | qemu-io -f raw nbd:unix:$sock >> truncate4.out || fail=1
+exec 4>&-
+
+cat truncate4.out
+grep 'Pattern verification failed' truncate4.out && fail=1
+exit $fail
-- 
2.20.1