[Libguestfs] [nbdkit PATCH 3/3] tests: Add regression test for NBDKIT_EMULATE_CACHE fix

[Eric Blake]

Add testsuite coverage for the bug fixed in the previous patch (done
separately, to make it easier to prove the test fails without the
patch).
---
 tests/Makefile.am        |  2 +
 tests/test-eval-cache.sh | 85 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 87 insertions(+)
 create mode 100755 tests/test-eval-cache.sh

diff --git a/tests/Makefile.am b/tests/Makefile.am
index 67e7618b..2ed21dc2 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -712,11 +712,13 @@ TESTS += \
 	test-eval.sh \
 	test-eval-file.sh \
 	test-eval-exports.sh \
+	test-eval-cache.sh \
 	$(NULL)
 EXTRA_DIST += \
 	test-eval.sh \
 	test-eval-file.sh \
 	test-eval-exports.sh \
+	test-eval-cache.sh \
 	$(NULL)

 # file plugin test.
diff --git a/tests/test-eval-cache.sh b/tests/test-eval-cache.sh
new file mode 100755
index 00000000..f523e03c
--- /dev/null
+++ b/tests/test-eval-cache.sh
@@ -0,0 +1,85 @@
+#!/usr/bin/env bash
+# nbdkit
+# Copyright (C) 2022 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.
+
+# Check that NBDKIT_CACHE_EMULATE works on large requests.
+
+source ./functions.sh
+set -e
+set -x
+
+requires_plugin eval
+requires_nbdsh_uri
+
+files="eval-cache.witness eval-cache.cache"
+rm -f $files
+cleanup_fn rm -f $files
+fail=0
+
+# This plugin requests nbdkit to emulate caching with pread. When the witness
+# file exists, cache reads; when absent, reads fail if not already cached.
+export witness="$PWD/eval-cache.witness"
+export cache="$PWD/eval-cache.cache"
+export script='
+import os
+import errno
+
+witness = os.getenv("witness")
+
+def touch(path):
+    open(path, "a").close()
+
+# Test that uncached read fails
+try:
+    h.pread(1024 * 1024, 0)
+except nbd.Error as ex:
+    assert ex.errnum == errno.EIO
+
+# Cache the entire image; nbdkit should break it into 64k preads
+touch(witness)
+h.cache(h.get_size(), 0)
+os.unlink(witness)
+
+# Now read should succeed
+buf = h.pread(64 * 1024 * 1024, 64 * 1024 * 1024)
+if hasattr(buf, "is_zero"):
+    assert buf.is_zero()
+'
+nbdkit -U - -v eval \
+    get_size='echo 128M' can_cache='echo emulate' open='touch "$cache"' \
+    pread='
+      if test -f "$witness"; then
+        echo "$3 $4" >> "$cache"
+      elif ! grep -q "^$3 $4$" "$cache"; then
+        echo EIO >&2; exit 1
+      fi
+      dd if=/dev/zero count=$3 iflag=count_bytes
+    ' --run 'nbdsh -u "$uri" -c "$script"'
-- 
2.36.1