Merge remote-tracking branch 'mreitz/tags/pull-block-2018-05-15' into queue-block

- Copy-on-read block driver
- The qcow2 default refcount cache size has been decreased
- Various bug fixes

# gpg: Signature made Tue May 15 16:18:25 2018 CEST
# gpg:                using RSA key F407DB0061D5CF40
# gpg: Good signature from "Max Reitz <mreitz@redhat.com>"
# Primary key fingerprint: 91BE B60A 30DB 3E88 57D1  1829 F407 DB00 61D5 CF40

* mreitz/tags/pull-block-2018-05-15: (21 commits)
  iotests: Add test for -U/force-share conflicts
  qemu-img: Use only string options in img_open_opts
  qemu-io: Use purely string blockdev options
  block: Document BDRV_REQ_WRITE_UNCHANGED support
  qemu-img: Check post-truncation size
  iotests: Add test for COR across nodes
  iotests: Copy 197 for COR filter driver
  iotests: Clean up wrap image in 197
  block: Support BDRV_REQ_WRITE_UNCHANGED in filters
  block/quorum: Support BDRV_REQ_WRITE_UNCHANGED
  block: Set BDRV_REQ_WRITE_UNCHANGED for COR writes
  block: Add BDRV_REQ_WRITE_UNCHANGED flag
  block: BLK_PERM_WRITE includes ..._UNCHANGED
  block: Add COR filter driver
  iotests: Skip 181 and 201 without userfaultfd
  iotests: Add failure matching to common.qemu
  docs: Document the new default sizes of the qcow2 caches
  qcow2: Give the refcount cache the minimum possible size by default
  specs/qcow2: Clarify that compressed clusters have the COPIED bit reset
  Fix error message about compressed clusters with OFLAG_COPIED
  ...

Signed-off-by: Kevin Wolf <kwolf@redhat.com>

16 files changed, 536 insertions, 88 deletions

diff --git a/tests/qemu-iotests/122 b/tests/qemu-iotests/122
index 6cf4fcb866..45b359c2ba 100755
--- a/tests/qemu-iotests/122
+++ b/tests/qemu-iotests/122
@@ -130,53 +130,6 @@ $QEMU_IO -c "read -P 0    1024k 1022k" "$TEST_IMG" 2>&1 | _filter_qemu_io | _fil
 
 
 echo
-echo "=== Corrupted size field in compressed cluster descriptor ==="
-echo
-# Create an empty image and fill half of it with compressed data.
-# The L2 entries of the two compressed clusters are located at
-# 0x800000 and 0x800008, their original values are 0x4008000000a00000
-# and 0x4008000000a00802 (5 sectors for compressed data each).
-_make_test_img 8M -o cluster_size=2M
-$QEMU_IO -c "write -c -P 0x11 0 2M" -c "write -c -P 0x11 2M 2M" "$TEST_IMG" \
-         2>&1 | _filter_qemu_io | _filter_testdir
-
-# Reduce size of compressed data to 4 sectors: this corrupts the image.
-poke_file "$TEST_IMG" $((0x800000)) "\x40\x06"
-$QEMU_IO -c "read  -P 0x11 0 4M" "$TEST_IMG" 2>&1 | _filter_qemu_io | _filter_testdir
-
-# 'qemu-img check' however doesn't see anything wrong because it
-# doesn't try to decompress the data and the refcounts are consistent.
-# TODO: update qemu-img so this can be detected.
-_check_test_img
-
-# Increase size of compressed data to the maximum (8192 sectors).
-# This makes QEMU read more data (8192 sectors instead of 5, host
-# addresses [0xa00000, 0xdfffff]), but the decompression algorithm
-# stops once we have enough to restore the uncompressed cluster, so
-# the rest of the data is ignored.
-poke_file "$TEST_IMG" $((0x800000)) "\x7f\xfe"
-# Do it also for the second compressed cluster (L2 entry at 0x800008).
-# In this case the compressed data would span 3 host clusters
-# (host addresses: [0xa00802, 0xe00801])
-poke_file "$TEST_IMG" $((0x800008)) "\x7f\xfe"
-
-# Here the image is too small so we're asking QEMU to read beyond the
-# end of the image.
-$QEMU_IO -c "read  -P 0x11  0 4M" "$TEST_IMG" 2>&1 | _filter_qemu_io | _filter_testdir
-# But if we grow the image we won't be reading beyond its end anymore.
-$QEMU_IO -c "write -P 0x22 4M 4M" "$TEST_IMG" 2>&1 | _filter_qemu_io | _filter_testdir
-$QEMU_IO -c "read  -P 0x11  0 4M" "$TEST_IMG" 2>&1 | _filter_qemu_io | _filter_testdir
-
-# The refcount data is however wrong because due to the increased size
-# of the compressed data it now reaches the following host clusters.
-# This can be repaired by qemu-img check by increasing the refcount of
-# those clusters.
-# TODO: update qemu-img to correct the compressed cluster size instead.
-_check_test_img -r all
-$QEMU_IO -c "read  -P 0x11  0 4M" "$TEST_IMG" 2>&1 | _filter_qemu_io | _filter_testdir
-$QEMU_IO -c "read  -P 0x22 4M 4M" "$TEST_IMG" 2>&1 | _filter_qemu_io | _filter_testdir
-
-echo
 echo "=== Full allocation with -S 0 ==="
 echo
 
diff --git a/tests/qemu-iotests/122.out b/tests/qemu-iotests/122.out
index a6b7fe007e..47d8656db8 100644
--- a/tests/qemu-iotests/122.out
+++ b/tests/qemu-iotests/122.out
@@ -99,39 +99,6 @@ read 1024/1024 bytes at offset 1047552
 read 1046528/1046528 bytes at offset 1048576
 1022 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 
-=== Corrupted size field in compressed cluster descriptor ===
-
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=8388608
-wrote 2097152/2097152 bytes at offset 0
-2 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
-wrote 2097152/2097152 bytes at offset 2097152
-2 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
-read failed: Input/output error
-No errors were found on the image.
-read 4194304/4194304 bytes at offset 0
-4 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
-wrote 4194304/4194304 bytes at offset 4194304
-4 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
-read 4194304/4194304 bytes at offset 0
-4 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
-ERROR cluster 6 refcount=1 reference=3
-ERROR cluster 7 refcount=1 reference=2
-Repairing cluster 6 refcount=1 reference=3
-Repairing cluster 7 refcount=1 reference=2
-Repairing OFLAG_COPIED data cluster: l2_entry=8000000000c00000 refcount=3
-Repairing OFLAG_COPIED data cluster: l2_entry=8000000000e00000 refcount=2
-The following inconsistencies were found and repaired:
-
-    0 leaked clusters
-    4 corruptions
-
-Double checking the fixed image now...
-No errors were found on the image.
-read 4194304/4194304 bytes at offset 0
-4 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
-read 4194304/4194304 bytes at offset 4194304
-4 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
-
 === Full allocation with -S 0 ===
 
 Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864
diff --git a/tests/qemu-iotests/137.out b/tests/qemu-iotests/137.out
index e28e1eadba..96724a6c33 100644
--- a/tests/qemu-iotests/137.out
+++ b/tests/qemu-iotests/137.out
@@ -22,7 +22,7 @@ refcount-cache-size may not exceed cache-size
 L2 cache size too big
 L2 cache entry size must be a power of two between 512 and the cluster size (65536)
 L2 cache entry size must be a power of two between 512 and the cluster size (65536)
-L2 cache size too big
+Refcount cache size too big
 Conflicting values for qcow2 options 'overlap-check' ('constant') and 'overlap-check.template' ('all')
 Unsupported value 'blubb' for qcow2 option 'overlap-check'. Allowed are any of the following: none, constant, cached, all
 Unsupported value 'blubb' for qcow2 option 'overlap-check'. Allowed are any of the following: none, constant, cached, all
diff --git a/tests/qemu-iotests/153 b/tests/qemu-iotests/153
index a0fd815483..ec508c758f 100755
--- a/tests/qemu-iotests/153
+++ b/tests/qemu-iotests/153
@@ -242,6 +242,23 @@ _run_cmd $QEMU_IO "${TEST_IMG}" -c 'write 0 512'
 
 _cleanup_qemu
 
+echo
+echo "== Detecting -U and force-share conflicts =="
+
+echo
+echo 'No conflict:'
+$QEMU_IMG info -U --image-opts driver=null-co,force-share=on
+echo
+echo 'Conflict:'
+$QEMU_IMG info -U --image-opts driver=null-co,force-share=off
+
+echo
+echo 'No conflict:'
+$QEMU_IO -c 'open -r -U -o driver=null-co,force-share=on'
+echo
+echo 'Conflict:'
+$QEMU_IO -c 'open -r -U -o driver=null-co,force-share=off'
+
 # success, all done
 echo "*** done"
 rm -f $seq.full
diff --git a/tests/qemu-iotests/153.out b/tests/qemu-iotests/153.out
index bb721cb747..2510762ba1 100644
--- a/tests/qemu-iotests/153.out
+++ b/tests/qemu-iotests/153.out
@@ -399,4 +399,20 @@ Is another process using the image?
 Closing the other
 
 _qemu_io_wrapper TEST_DIR/t.qcow2 -c write 0 512
+
+== Detecting -U and force-share conflicts ==
+
+No conflict:
+image: null-co://
+file format: null-co
+virtual size: 1.0G (1073741824 bytes)
+disk size: unavailable
+
+Conflict:
+qemu-img: --force-share/-U conflicts with image options
+
+No conflict:
+
+Conflict:
+-U conflicts with image options
 *** done
diff --git a/tests/qemu-iotests/181 b/tests/qemu-iotests/181
index 5e767c6195..e02979378d 100755
--- a/tests/qemu-iotests/181
+++ b/tests/qemu-iotests/181
@@ -96,6 +96,19 @@ echo
 # Enable postcopy-ram capability both on source and destination
 silent=yes
 _send_qemu_cmd $dest 'migrate_set_capability postcopy-ram on' "(qemu)"
+
+qemu_error_no_exit=yes success_or_failure=yes \
+    _send_qemu_cmd $dest '' "(qemu)" "Postcopy is not supported"
+if [ ${QEMU_STATUS[$dest]} -lt 0 ]; then
+    _send_qemu_cmd $dest '' "(qemu)"
+
+    _send_qemu_cmd $src 'quit' ""
+    _send_qemu_cmd $dest 'quit' ""
+    wait=1 _cleanup_qemu
+
+    _notrun 'Postcopy is not supported'
+fi
+
 _send_qemu_cmd $src 'migrate_set_speed 4k' "(qemu)"
 _send_qemu_cmd $src 'migrate_set_capability postcopy-ram on' "(qemu)"
 _send_qemu_cmd $src "migrate -d unix:${MIG_SOCKET}" "(qemu)"
diff --git a/tests/qemu-iotests/197 b/tests/qemu-iotests/197
index 5e869fe2b7..3ae4975eec 100755
--- a/tests/qemu-iotests/197
+++ b/tests/qemu-iotests/197
@@ -44,6 +44,7 @@ esac
 _cleanup()
 {
     _cleanup_test_img
+    rm -f "$TEST_WRAP"
     rm -f "$BLKDBG_CONF"
 }
 trap "_cleanup; exit \$status" 0 1 2 3 15
diff --git a/tests/qemu-iotests/201 b/tests/qemu-iotests/201
index 11f640f5df..c1a1e00077 100755
--- a/tests/qemu-iotests/201
+++ b/tests/qemu-iotests/201
@@ -82,6 +82,19 @@ echo
 
 silent=yes
 _send_qemu_cmd $dest 'migrate_set_capability postcopy-ram on' "(qemu)"
+
+qemu_error_no_exit=yes success_or_failure=yes \
+    _send_qemu_cmd $dest '' "(qemu)" "Postcopy is not supported"
+if [ ${QEMU_STATUS[$dest]} -lt 0 ]; then
+    _send_qemu_cmd $dest '' "(qemu)"
+
+    _send_qemu_cmd $src 'quit' ""
+    _send_qemu_cmd $dest 'quit' ""
+    wait=1 _cleanup_qemu
+
+    _notrun 'Postcopy is not supported'
+fi
+
 _send_qemu_cmd $src 'migrate_set_capability postcopy-ram on' "(qemu)"
 _send_qemu_cmd $src "migrate -d unix:${MIG_SOCKET}" "(qemu)"
 
diff --git a/tests/qemu-iotests/214 b/tests/qemu-iotests/214
new file mode 100755
index 0000000000..c46ca2a6dd
--- /dev/null
+++ b/tests/qemu-iotests/214
@@ -0,0 +1,97 @@
+#!/bin/bash
+#
+# Test qcow2 image compression
+#
+# Copyright (C) 2018 Igalia, S.L.
+# Author: Alberto Garcia <berto@igalia.com>
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+
+seq=$(basename "$0")
+echo "QA output created by $seq"
+
+here=$PWD
+status=1	# failure is the default!
+
+_cleanup()
+{
+    _cleanup_test_img
+}
+trap "_cleanup; exit \$status" 0 1 2 3 15
+
+# get standard environment, filters and checks
+. ./common.rc
+. ./common.filter
+
+_supported_fmt qcow2
+_supported_proto file
+_supported_os Linux
+
+# Repairing the corrupted image requires qemu-img check to store a
+# refcount up to 3, which requires at least two refcount bits.
+_unsupported_imgopts 'refcount_bits=1[^0-9]'
+
+
+echo
+echo "=== Corrupted size field in compressed cluster descriptor ==="
+echo
+# Create an empty image and fill half of it with compressed data.
+# The L2 entries of the two compressed clusters are located at
+# 0x800000 and 0x800008, their original values are 0x4008000000a00000
+# and 0x4008000000a00802 (5 sectors for compressed data each).
+_make_test_img 8M -o cluster_size=2M
+$QEMU_IO -c "write -c -P 0x11 0 2M" -c "write -c -P 0x11 2M 2M" "$TEST_IMG" \
+         2>&1 | _filter_qemu_io | _filter_testdir
+
+# Reduce size of compressed data to 4 sectors: this corrupts the image.
+poke_file "$TEST_IMG" $((0x800000)) "\x40\x06"
+$QEMU_IO -c "read  -P 0x11 0 4M" "$TEST_IMG" 2>&1 | _filter_qemu_io | _filter_testdir
+
+# 'qemu-img check' however doesn't see anything wrong because it
+# doesn't try to decompress the data and the refcounts are consistent.
+# TODO: update qemu-img so this can be detected.
+_check_test_img
+
+# Increase size of compressed data to the maximum (8192 sectors).
+# This makes QEMU read more data (8192 sectors instead of 5, host
+# addresses [0xa00000, 0xdfffff]), but the decompression algorithm
+# stops once we have enough to restore the uncompressed cluster, so
+# the rest of the data is ignored.
+poke_file "$TEST_IMG" $((0x800000)) "\x7f\xfe"
+# Do it also for the second compressed cluster (L2 entry at 0x800008).
+# In this case the compressed data would span 3 host clusters
+# (host addresses: [0xa00802, 0xe00801])
+poke_file "$TEST_IMG" $((0x800008)) "\x7f\xfe"
+
+# Here the image is too small so we're asking QEMU to read beyond the
+# end of the image.
+$QEMU_IO -c "read  -P 0x11  0 4M" "$TEST_IMG" 2>&1 | _filter_qemu_io | _filter_testdir
+# But if we grow the image we won't be reading beyond its end anymore.
+$QEMU_IO -c "write -P 0x22 4M 4M" "$TEST_IMG" 2>&1 | _filter_qemu_io | _filter_testdir
+$QEMU_IO -c "read  -P 0x11  0 4M" "$TEST_IMG" 2>&1 | _filter_qemu_io | _filter_testdir
+
+# The refcount data is however wrong because due to the increased size
+# of the compressed data it now reaches the following host clusters.
+# This can be repaired by qemu-img check by increasing the refcount of
+# those clusters.
+# TODO: update qemu-img to correct the compressed cluster size instead.
+_check_test_img -r all
+$QEMU_IO -c "read  -P 0x11  0 4M" "$TEST_IMG" 2>&1 | _filter_qemu_io | _filter_testdir
+$QEMU_IO -c "read  -P 0x22 4M 4M" "$TEST_IMG" 2>&1 | _filter_qemu_io | _filter_testdir
+
+# success, all done
+echo '*** done'
+rm -f $seq.full
+status=0
diff --git a/tests/qemu-iotests/214.out b/tests/qemu-iotests/214.out
new file mode 100644
index 0000000000..0fcd8dc051
--- /dev/null
+++ b/tests/qemu-iotests/214.out
@@ -0,0 +1,35 @@
+QA output created by 214
+
+=== Corrupted size field in compressed cluster descriptor ===
+
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=8388608
+wrote 2097152/2097152 bytes at offset 0
+2 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+wrote 2097152/2097152 bytes at offset 2097152
+2 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+read failed: Input/output error
+No errors were found on the image.
+read 4194304/4194304 bytes at offset 0
+4 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+wrote 4194304/4194304 bytes at offset 4194304
+4 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+read 4194304/4194304 bytes at offset 0
+4 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+ERROR cluster 6 refcount=1 reference=3
+ERROR cluster 7 refcount=1 reference=2
+Repairing cluster 6 refcount=1 reference=3
+Repairing cluster 7 refcount=1 reference=2
+Repairing OFLAG_COPIED data cluster: l2_entry=8000000000c00000 refcount=3
+Repairing OFLAG_COPIED data cluster: l2_entry=8000000000e00000 refcount=2
+The following inconsistencies were found and repaired:
+
+    0 leaked clusters
+    4 corruptions
+
+Double checking the fixed image now...
+No errors were found on the image.
+read 4194304/4194304 bytes at offset 0
+4 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+read 4194304/4194304 bytes at offset 4194304
+4 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+*** done
diff --git a/tests/qemu-iotests/215 b/tests/qemu-iotests/215
new file mode 100755
index 0000000000..2e616ed659
--- /dev/null
+++ b/tests/qemu-iotests/215
@@ -0,0 +1,120 @@
+#!/bin/bash
+#
+# Test case for copy-on-read into qcow2, using the COR filter driver
+#
+# Copyright (C) 2018 Red Hat, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+
+seq="$(basename $0)"
+echo "QA output created by $seq"
+
+here="$PWD"
+status=1 # failure is the default!
+
+# get standard environment, filters and checks
+. ./common.rc
+. ./common.filter
+
+TEST_WRAP="$TEST_DIR/t.wrap.qcow2"
+BLKDBG_CONF="$TEST_DIR/blkdebug.conf"
+
+# Sanity check: our use of blkdebug fails if $TEST_DIR contains spaces
+# or other problems
+case "$TEST_DIR" in
+    *[^-_a-zA-Z0-9/]*)
+        _notrun "Suspicious TEST_DIR='$TEST_DIR', cowardly refusing to run" ;;
+esac
+
+_cleanup()
+{
+    _cleanup_test_img
+    rm -f "$TEST_WRAP"
+    rm -f "$BLKDBG_CONF"
+}
+trap "_cleanup; exit \$status" 0 1 2 3 15
+
+# Test is supported for any backing file; but we force qcow2 for our wrapper.
+_supported_fmt generic
+_supported_proto generic
+_supported_os Linux
+# LUKS support may be possible, but it complicates things.
+_unsupported_fmt luks
+
+echo
+echo '=== Copy-on-read ==='
+echo
+
+# Prep the images
+# VPC rounds image sizes to a specific geometry, force a specific size.
+if [ "$IMGFMT" = "vpc" ]; then
+    IMGOPTS=$(_optstr_add "$IMGOPTS" "force_size")
+fi
+_make_test_img 4G
+$QEMU_IO -c "write -P 55 3G 1k" "$TEST_IMG" | _filter_qemu_io
+IMGPROTO=file IMGFMT=qcow2 IMGOPTS= TEST_IMG_FILE="$TEST_WRAP" \
+    _make_test_img -F "$IMGFMT" -b "$TEST_IMG" | _filter_img_create
+$QEMU_IO -f qcow2 -c "write -z -u 1M 64k" "$TEST_WRAP" | _filter_qemu_io
+
+# Ensure that a read of two clusters, but where one is already allocated,
+# does not re-write the allocated cluster
+cat > "$BLKDBG_CONF" <<EOF
+[inject-error]
+event = "cor_write"
+sector = "2048"
+EOF
+$QEMU_IO -c "open \
+ -o driver=copy-on-read,file.driver=blkdebug,file.config=$BLKDBG_CONF,file.image.driver=qcow2 $TEST_WRAP" \
+ -c "read -P 0 1M 128k" | _filter_qemu_io
+
+# Read the areas we want copied. A zero-length read should still be a
+# no-op.  The next read is under 2G, but aligned so that rounding to
+# clusters copies more than 2G of zeroes. The final read will pick up
+# the non-zero data in the same cluster.  Since a 2G read may exhaust
+# memory on some machines (particularly 32-bit), we skip the test if
+# that fails due to memory pressure.
+$QEMU_IO \
+    -c "open -o driver=copy-on-read,file.driver=qcow2 $TEST_WRAP" \
+    -c "read 0 0" \
+    | _filter_qemu_io
+output=$($QEMU_IO \
+         -c "open -o driver=copy-on-read,file.driver=qcow2 $TEST_WRAP" \
+         -c "read -P 0 1k $((2*1024*1024*1024 - 512))" \
+         2>&1 | _filter_qemu_io)
+case $output in
+    *allocate*)
+        _notrun "Insufficent memory to run test" ;;
+    *) printf '%s\n' "$output" ;;
+esac
+$QEMU_IO \
+    -c "open -o driver=copy-on-read,file.driver=qcow2 $TEST_WRAP" \
+    -c "read -P 0 $((3*1024*1024*1024 + 1024)) 1k" \
+    | _filter_qemu_io
+
+# Copy-on-read is incompatible with read-only
+$QEMU_IO \
+    -c "open -r -o driver=copy-on-read,file.driver=qcow2 $TEST_WRAP" \
+    2>&1 | _filter_testdir
+
+# Break the backing chain, and show that images are identical, and that
+# we properly copied over explicit zeros.
+$QEMU_IMG rebase -u -b "" -f qcow2 "$TEST_WRAP"
+$QEMU_IO -f qcow2 -c map "$TEST_WRAP"
+_check_test_img
+$QEMU_IMG compare -f $IMGFMT -F qcow2 "$TEST_IMG" "$TEST_WRAP"
+
+# success, all done
+echo '*** done'
+status=0
diff --git a/tests/qemu-iotests/215.out b/tests/qemu-iotests/215.out
new file mode 100644
index 0000000000..70b0f5fb19
--- /dev/null
+++ b/tests/qemu-iotests/215.out
@@ -0,0 +1,26 @@
+QA output created by 215
+
+=== Copy-on-read ===
+
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=4294967296
+wrote 1024/1024 bytes at offset 3221225472
+1 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+Formatting 'TEST_DIR/t.wrap.IMGFMT', fmt=IMGFMT size=4294967296 backing_file=TEST_DIR/t.IMGFMT backing_fmt=IMGFMT
+wrote 65536/65536 bytes at offset 1048576
+64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+read 131072/131072 bytes at offset 1048576
+128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+read 0/0 bytes at offset 0
+0 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+read 2147483136/2147483136 bytes at offset 1024
+2 GiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+read 1024/1024 bytes at offset 3221226496
+1 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+can't open device TEST_DIR/t.wrap.qcow2: Block node is read-only
+2 GiB (0x80010000) bytes     allocated at offset 0 bytes (0x0)
+1023.938 MiB (0x3fff0000) bytes not allocated at offset 2 GiB (0x80010000)
+64 KiB (0x10000) bytes     allocated at offset 3 GiB (0xc0000000)
+1023.938 MiB (0x3fff0000) bytes not allocated at offset 3 GiB (0xc0010000)
+No errors were found on the image.
+Images are identical.
+*** done
diff --git a/tests/qemu-iotests/216 b/tests/qemu-iotests/216
new file mode 100755
index 0000000000..ca9b47a7fd
--- /dev/null
+++ b/tests/qemu-iotests/216
@@ -0,0 +1,115 @@
+#!/usr/bin/env python
+#
+# Copy-on-read tests using a COR filter node
+#
+# Copyright (C) 2018 Red Hat, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+# Creator/Owner: Max Reitz <mreitz@redhat.com>
+
+import iotests
+from iotests import log, qemu_img_pipe, qemu_io, filter_qemu_io
+
+# Need backing file support
+iotests.verify_image_format(supported_fmts=['qcow2', 'qcow', 'qed', 'vmdk'])
+iotests.verify_platform(['linux'])
+
+log('')
+log('=== Copy-on-read across nodes ===')
+log('')
+
+# The old copy-on-read mechanism without a filter node cannot request
+# WRITE_UNCHANGED permissions for its child.  Therefore it just tries
+# to sneak its write by the usual permission system and holds its
+# fingers crossed.  However, that sneaking does not work so well when
+# there is a filter node in the way: That will receive the write
+# request and re-issue a new one to its child, which this time is a
+# proper write request that will make the permission system cough --
+# unless there is someone at the top (like a guest device) that has
+# requested write permissions.
+#
+# A COR filter node, however, can request the proper permissions for
+# its child and therefore is not hit by this issue.
+
+with iotests.FilePath('base.img') as base_img_path, \
+     iotests.FilePath('top.img') as top_img_path, \
+     iotests.VM() as vm:
+
+    log('--- Setting up images ---')
+    log('')
+
+    qemu_img_pipe('create', '-f', iotests.imgfmt, base_img_path, '64M')
+
+    log(filter_qemu_io(qemu_io(base_img_path, '-c', 'write -P 1 0M 1M')))
+
+    qemu_img_pipe('create', '-f', iotests.imgfmt, '-b', base_img_path,
+                  top_img_path)
+
+    log(filter_qemu_io(qemu_io(top_img_path,  '-c', 'write -P 2 1M 1M')))
+
+    log('')
+    log('--- Doing COR ---')
+    log('')
+
+    # Compare with e.g. the following:
+    #   vm.add_drive_raw('if=none,node-name=node0,copy-on-read=on,driver=raw,' \
+    #                    'file.driver=%s,file.file.filename=%s' %
+    #                       (iotests.imgfmt, top_img_path))
+    # (Remove the blockdev-add instead.)
+    # ((Not tested here because it hits an assertion in the permission
+    #   system.))
+
+    vm.launch()
+
+    log(vm.qmp('blockdev-add',
+                    node_name='node0',
+                    driver='copy-on-read',
+                    file={
+                        'driver': 'raw',
+                        'file': {
+                            'driver': 'copy-on-read',
+                            'file': {
+                                'driver': 'raw',
+                                'file': {
+                                    'driver': iotests.imgfmt,
+                                    'file': {
+                                        'driver': 'file',
+                                        'filename': top_img_path
+                                    },
+                                    'backing': {
+                                        'driver': iotests.imgfmt,
+                                        'file': {
+                                            'driver': 'file',
+                                            'filename': base_img_path
+                                        }
+                                    }
+                                }
+                            }
+                        }
+                    }))
+
+    # Trigger COR
+    log(vm.qmp('human-monitor-command',
+               command_line='qemu-io node0 "read 0 64M"'))
+
+    vm.shutdown()
+
+    log('')
+    log('--- Checking COR result ---')
+    log('')
+
+    log(filter_qemu_io(qemu_io(base_img_path, '-c', 'discard 0 64M')))
+    log(filter_qemu_io(qemu_io(top_img_path,  '-c', 'read -P 1 0M 1M')))
+    log(filter_qemu_io(qemu_io(top_img_path,  '-c', 'read -P 2 1M 1M')))
diff --git a/tests/qemu-iotests/216.out b/tests/qemu-iotests/216.out
new file mode 100644
index 0000000000..d3fc590d29
--- /dev/null
+++ b/tests/qemu-iotests/216.out
@@ -0,0 +1,28 @@
+
+=== Copy-on-read across nodes ===
+
+--- Setting up images ---
+
+wrote 1048576/1048576 bytes at offset 0
+1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+
+wrote 1048576/1048576 bytes at offset 1048576
+1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+
+
+--- Doing COR ---
+
+{u'return': {}}
+{u'return': u''}
+
+--- Checking COR result ---
+
+discard 67108864/67108864 bytes at offset 0
+64 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+
+read 1048576/1048576 bytes at offset 0
+1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+
+read 1048576/1048576 bytes at offset 1048576
+1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+
diff --git a/tests/qemu-iotests/common.qemu b/tests/qemu-iotests/common.qemu
index 85f66b852c..f285484951 100644
--- a/tests/qemu-iotests/common.qemu
+++ b/tests/qemu-iotests/common.qemu
@@ -52,11 +52,29 @@ _in_fd=4
 # response is not echoed out.
 # If $mismatch_only is set, only non-matching responses will
 # be echoed.
+#
+# If $success_or_failure is set, the meaning of the arguments is
+# changed as follows:
+# $2: A string to search for in the response; if found, this indicates
+#     success and ${QEMU_STATUS[$1]} is set to 0.
+# $3: A string to search for in the response; if found, this indicates
+#     failure and the test is either aborted (if $qemu_error_no_exit
+#     is not set) or ${QEMU_STATUS[$1]} is set to -1 (otherwise).
 function _timed_wait_for()
 {
     local h=${1}
     shift
 
+    if [ -z "${success_or_failure}" ]; then
+        success_match=${*}
+        failure_match=
+    else
+        success_match=${1}
+        failure_match=${2}
+    fi
+
+    timeout=yes
+
     QEMU_STATUS[$h]=0
     while IFS= read -t ${QEMU_COMM_TIMEOUT} resp <&${QEMU_OUT[$h]}
     do
@@ -64,10 +82,18 @@ function _timed_wait_for()
             echo "${resp}" | _filter_testdir | _filter_qemu \
                            | _filter_qemu_io | _filter_qmp | _filter_hmp
         fi
-        grep -q "${*}" < <(echo "${resp}")
+        if [ -n "${failure_match}" ]; then
+            grep -q "${failure_match}" < <(echo "${resp}")
+            if [ $? -eq 0 ]; then
+                timeout=
+                break
+            fi
+        fi
+        grep -q "${success_match}" < <(echo "${resp}")
         if [ $? -eq 0 ]; then
             return
-        elif [ -z "${silent}" ] && [ -n "${mismatch_only}" ]; then
+        fi
+        if [ -z "${silent}" ] && [ -n "${mismatch_only}" ]; then
             echo "${resp}" | _filter_testdir | _filter_qemu \
                            | _filter_qemu_io | _filter_qmp | _filter_hmp
         fi
@@ -75,8 +101,12 @@ function _timed_wait_for()
     done
     QEMU_STATUS[$h]=-1
     if [ -z "${qemu_error_no_exit}" ]; then
-        echo "Timeout waiting for ${*} on handle ${h}"
-        exit 1  # Timeout means the test failed
+        if [ -n "${timeout}" ]; then
+            echo "Timeout waiting for ${success_match} on handle ${h}"
+        else
+            echo "Wrong response matching ${failure_match} on handle ${h}"
+        fi
+        exit 1  # Timeout or wrong match mean the test failed
     fi
 }
 
@@ -96,6 +126,11 @@ function _timed_wait_for()
 # If $qemu_error_no_exit is set, then even if the expected response
 # is not seen, we will not exit.  $QEMU_STATUS[$1] will be set it -1 in
 # that case.
+#
+# If $success_or_failure is set, then the last two strings are the
+# strings the response will be scanned for.  The first of the two
+# indicates success, the latter indicates failure.  Failure is handled
+# like a timeout.
 function _send_qemu_cmd()
 {
     local h=${1}
@@ -109,14 +144,23 @@ function _send_qemu_cmd()
         use_error="no"
     fi
     # This array element extraction is done to accommodate pathnames with spaces
-    cmd=${@: 1:${#@}-1}
-    shift $(($# - 1))
+    if [ -z "${success_or_failure}" ]; then
+        cmd=${@: 1:${#@}-1}
+        shift $(($# - 1))
+    else
+        cmd=${@: 1:${#@}-2}
+        shift $(($# - 2))
+    fi
 
     while [ ${count} -gt 0 ]
     do
         echo "${cmd}" >&${QEMU_IN[${h}]}
         if [ -n "${1}" ]; then
-            qemu_error_no_exit=${use_error} _timed_wait_for ${h} "${1}"
+            if [ -z "${success_or_failure}" ]; then
+                qemu_error_no_exit=${use_error} _timed_wait_for ${h} "${1}"
+            else
+                qemu_error_no_exit=${use_error} _timed_wait_for ${h} "${1}" "${2}"
+            fi
             if [ ${QEMU_STATUS[$h]} -eq 0 ]; then
                 return
             fi
diff --git a/tests/qemu-iotests/group b/tests/qemu-iotests/group
index 5daef24020..cc8cd8cc8e 100644
--- a/tests/qemu-iotests/group
+++ b/tests/qemu-iotests/group
@@ -212,4 +212,7 @@
 211 rw auto quick
 212 rw auto quick
 213 rw auto quick
+214 rw auto
+215 rw auto quick
+216 rw auto quick
 218 rw auto quick