tests/btrfs/081

#! /bin/bash
# SPDX-License-Identifier: GPL-2.0
# Copyright (C) 2014 SUSE Linux Products GmbH. All Rights Reserved.
#
# FSQA Test No. 081
#
# Regression test for a btrfs clone ioctl issue where races between
# a clone operation and concurrent target file reads would result in
# leaving stale data in the page cache. After the clone operation
# finished, reading from the clone target file would return the old
# and no longer valid data. This affected only buffered reads (i.e.
# didn't affect direct IO reads).
#
# This issue was fixed by the following linux kernel patch:
#
#     Btrfs: ensure readers see new data after a clone operation
#     (commit c125b8bff1d9f6c8c91ce4eb8bd5616058c7d510)
#
seq=`basename $0`
seqres=$RESULT_DIR/$seq
echo "QA output created by $seq"
tmp=/tmp/$$
status=1	# failure is the default!
trap "_cleanup; exit \$status" 0 1 2 3 15

_cleanup()
{
	rm -f $tmp.*
}

# get standard environment, filters and checks
. ./common/rc
. ./common/filter

# real QA test starts here
_supported_fs btrfs
_require_scratch
_require_cloner

rm -f $seqres.full

num_extents=100
extent_size=8192

create_source_file()
{
	local name=$1

	# Create a file with $num_extents extents, each with a size of
	# $extent_size bytes.
	touch $SCRATCH_MNT/$name
	for ((i = 0; i < $num_extents; i++)); do
		off=$((i * $extent_size))
		$XFS_IO_PROG \
			-c "pwrite -S $i -b $extent_size $off $extent_size" \
			-c "fsync" $SCRATCH_MNT/$name | _filter_xfs_io
	done
}

create_target_file()
{
	local name=$1
	local file_size=$(($num_extents * $extent_size))

	$XFS_IO_PROG -f -c "pwrite -S 0xff 0 $file_size" \
		-c "fsync" $SCRATCH_MNT/$name | _filter_xfs_io
}

reader_loop()
{
	# Wait for any running 'cat' subcommand before exitting so that after
	# the test kills the reader loop subshell it does not fail with an
	# error message from a 'cat' subcommand due to the test file being
	# temporarily unavailable due to the scratch fs unmount operation.
	trap "wait; exit" SIGTERM

	local name=$1

	while true; do
		cat $SCRATCH_MNT/$name > /dev/null
	done
}

_scratch_mkfs >>$seqres.full 2>&1
_scratch_mount

echo "Creating source file..."
create_source_file "foo"
echo "Creating target file..."
create_target_file "bar"

reader_loop "bar" &
reader_pid=$!

$CLONER_PROG -s 0 -d 0 -l $(($num_extents * $extent_size)) \
	$SCRATCH_MNT/foo $SCRATCH_MNT/bar

kill $reader_pid > /dev/null 2>&1

# Now both foo and bar should have exactly the same content.
# This didn't use to be the case before the btrfs kernel fix mentioned
# above. The clone ioctl was racy, as it removed bar's pages from the
# page cache and only after it would update bar's metadata to point to
# the same extents that foo's metadata points to - and this was done in
# an unprotected way, so that a file read request done right after the
# clone ioctl removed the pages from the page cache and before it updated
# bar's metadata, would result in populating the page cache with stale
# data. Therefore a file read after the clone operation finished would
# not get the cloned data but it would get instead the old and no longer
# valid data.
echo "Verifying file digests after cloning"
md5sum $SCRATCH_MNT/foo | _filter_scratch
md5sum $SCRATCH_MNT/bar | _filter_scratch

# Validate the content of bar still matches foo's content even after
# clearing all of bar's data from the page cache.
_scratch_cycle_mount
echo "Verifying target file digest after umount + mount"
md5sum $SCRATCH_MNT/bar | _filter_scratch

status=0
exit