tests: Improve test-readahead test.

See
https://www.redhat.com/archives/libguestfs/2019-December/msg00088.html

tests/Makefile.am

@@ -168,7 +168,10 @@ EXTRA_DIST = \
 	test-rate.sh \
 	test-rate-dynamic.sh \
 	test.rb \
+	test-readahead.sh \
 	test-readahead-copy.sh \
+	test-readahead-test-plugin.sh \
+	test-readahead-test-request.py \
 	test-retry.sh \
 	test-retry-extents.sh \
 	test-retry-size.sh \
@@ -1050,12 +1053,10 @@ TESTS += \
 	$(NULL)
 
 # readahead filter test.
-LIBGUESTFS_TESTS += test-readahead
-TESTS += test-readahead-copy.sh
-
-test_readahead_SOURCES = test-readahead.c test.h
-test_readahead_CFLAGS = $(WARNINGS_CFLAGS) $(LIBGUESTFS_CFLAGS)
-test_readahead_LDADD = libtest.la $(LIBGUESTFS_LIBS)
+TESTS += \
+	test-readahead.sh \
+	test-readahead-copy.sh \
+	$(NULL)
 
 # retry filter test.
 TESTS += \

tests/test-readahead-test-plugin.sh

@@ -0,0 +1,48 @@
+#!/usr/bin/env bash
+# nbdkit
+# Copyright (C) 2018-2019 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.
+
+# Test plugin used by test-readahead.sh.
+
+case "$1" in
+    get_size)
+        # test-readahead-test-request.py will make 10 requests of 512
+        # bytes each, so this just has to be >= 512*10.
+        echo 1M
+        ;;
+    pread)
+        sleep 5
+        dd if=/dev/zero count=$3 iflag=count_bytes
+        ;;
+    *)
+        exit 2
+        ;;
+esac

tests/test-readahead-test-request.py

@@ -0,0 +1,44 @@
+#!/usr/bin/env python3
+# -*- python -*-
+# nbdkit
+# Copyright (C) 2018-2019 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.
+
+# Used by test-readahead.sh to make a linear series of requests
+# with a constant, known size.
+
+import nbd
+import sys
+
+h = nbd.NBD ()
+h.connect_unix (sys.argv[1])
+
+for i in range (0, 512*10, 512):
+    h.pread (512, i)

tests/test-readahead.sh

@@ -0,0 +1,67 @@
+#!/usr/bin/env bash
+# nbdkit
+# Copyright (C) 2018-2019 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.
+
+# Is the readahead filter faster?  Copy a blank disk with a custom
+# plugin that sleeps on every request.  Because the readahead filter
+# should result in fewer requests it should run faster.
+
+source ./functions.sh
+set -e
+set -x
+
+requires python3 --version
+requires python3 -c 'import nbd'
+
+files="readahead.img"
+rm -f $files
+cleanup_fn rm -f $files
+
+test ()
+{
+    start_t=$SECONDS
+    nbdkit -fv -U - "$@" sh ./test-readahead-test-plugin.sh \
+           --run './test-readahead-test-request.py $unixsocket'
+    end_t=$SECONDS
+    echo $((end_t - start_t))
+}
+
+t1=$(test --filter=readahead)
+t2=$(test)
+
+# In the t1 case we should make only 1 request into the plugin,
+# resulting in around 1 sleep period (5 seconds).  In the t2 case we
+# make 10 requests so sleep for around 50 seconds.  t1 should be < t2
+# is every reasonable scenario.
+if [ $t1 -ge $t2 ]; then
+    echo "$0: readahead filter took longer, should be shorter"
+    exit 1
+fi