Summary:

Add new testcase for testing the new btrfs sysfs knob to change the
chunk size. The new knob uses /sys/fs/btrfs/<UUID>/allocation/<block
type>/chunk_size.

The test case implements three different cases:
- Test allocation with the default chunk size
- Test allocation after increasing the chunk size
- Test allocation when the free space is smaller than the chunk size.

Note: this test needs to force the allocation of space. It uses the
/sys/fs/btrfs/<UUID>/allocation/<block type>/force_chunk_alloc knob.

Testing:
The test has been run with volumes of different sizes.

Signed-off-by: Stefan Roesch <redacted>
---
V3: - removed tests for system block type.
    - added failure case for system block type.
    - renamed stripe_size to chunk_size
V2: - added new functions to common/btrfs and use them in the new test
      - _require_btrfs_sysfs_attr - Make sure btrfs supports a sysfs
        setting
      - _get_btrfs_sysfs_attr - Read sysfs value
      - _set_btrfs_sysfs_attr - Write sysfs value
    - create file system of required size with _scratch_mkfs_sized
    - use shortened error message
    - Remove last logging message
---
 common/btrfs        |  73 ++++++++++++
 tests/btrfs/248     | 284 ++++++++++++++++++++++++++++++++++++++++++++
 tests/btrfs/248.out |  12 ++
 3 files changed, 369 insertions(+)
 create mode 100755 tests/btrfs/248
 create mode 100644 tests/btrfs/248.out

diff --git a/common/btrfs b/common/btrfs
index ac880bdd..759a0054 100644
--- a/common/btrfs
+++ b/common/btrfs

@@ -445,3 +445,76 @@ _scratch_btrfs_is_zoned()
 	[ `_zone_type ${SCRATCH_DEV}` != "none" ] && return 0
 	return 1
 }
+
+# Print the content of /sys/fs/btrfs/$UUID/$ATTR
+#
+# All arguments are necessary, and in this order:
+#  - mnt: mount point name, e.g. $SCRATCH_MNT
+#  - attr: path name under /sys/fs/btrfs/$uuid/$attr
+#
+# Usage example:
+#   _get_btrfs_sysfs_attr /mnt/scratch allocation/data/stripe_size
+_get_btrfs_sysfs_attr()
+{
+	local mnt=$1
+	local attr=$2
+
+	if [ ! -e "$mnt" -o -z "$attr" ];then
+		_fail "Usage: _get_btrfs_sysfs_attr <mounted_directory> <attr>"
+	fi
+
+	local uuid=$(findmnt -n -o UUID ${mnt})
+	cat /sys/fs/btrfs/${uuid}/${attr}
+}
+
+# Write "content" into /sys/fs/btrfs/$UUID/$ATTR
+#
+# All arguments are necessary, and in this order:
+#  - mnt: mount point name, e.g. $SCRATCH_MNT
+#  - attr: path name under /sys/fs/btrfs/$uuid/$attr
+#  - content: the content of $attr
+#
+# Usage example:
+#   _set_btrfs_sysfs_attr /mnt/scratch allocation/data/chunk_size
+_set_btrfs_sysfs_attr()
+{
+	local mnt=$1
+	shift
+	local attr=$1
+	shift
+	local content="$*"
+
+	if [ ! -e "$mnt" -o -z "$attr" -o -z "$content" ];then
+		_fail "Usage: _set_btrfs_sysfs_attr <mounted_directory> <attr> <content>"
+	fi
+
+	local uuid=$(findmnt -n -o UUID ${mnt})
+	echo "$content" > /sys/fs/btrfs/${uuid}/${attr} 2>&1
+	if [ $? -ne 0 ]; then
+		_log_err "_set_btrfs_sysfs_attr cannot write ${attr}"
+	fi
+}
+
+# Verify if the sysfs entry in /sys/fs/btrfs/$UUID/$ATTR exists
+#
+# All arguments are necessary, and in this order:
+#  - mnt: mount point name, e.g. $SCRATCH_MNT
+#  - attr: path name under /sys/fs/btrfs/$uuid/$attr
+#
+# Usage example:
+#   _require_btrfs_sysfs_attr /mnt/scratch allocation/data/chunk_size
+_require_btrfs_sysfs_attr()
+{
+	local mnt=$1
+	local attr=$2
+
+	if [ ! -e "$mnt" -o -z "$attr" ];then
+		_fail "Usage: _get_btrfs_sysfs_attr <mounted_directory> <attr>"
+	fi
+
+	local uuid=$(findmnt -n -o UUID ${mnt})
+  	if [[ ! -e  /sys/fs/btrfs/${uuid}/${attr} ]]; then
+			_notrun "Btrfs does not support sysfs $attr"
+	fi

+}
+

diff --git a/tests/btrfs/248 b/tests/btrfs/248
new file mode 100755
index 00000000..ae7e8039
--- /dev/null
+++ b/tests/btrfs/248

@@ -0,0 +1,284 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2021 Facebook.  All Rights Reserved.
+#
+# FS QA Test 250
+#
+# Test the new /sys/fs/btrfs/<uuid>/allocation/<block-type>/chunk_size
+# setting. This setting allows the admin to change the chunk size
+# setting for the next allocation.
+#
+# Test 1:
+#   Allocate storage for all three block types (data, metadata and system)
+#   with the default chunk size.
+#
+# Test 2:
+#   Set a new chunk size to double the default size and allocate space
+#   for all new block types with the new chunk size.
+#
+# Test 3:
+#   Pick an allocation size that is used in a loop and make sure the last
+#   allocation cannot be partially fullfilled.
+#
+# Note: Variable naming uses the following convention: if a variable name
+#       ends in "_B" then its a byte value, if it ends in "_MB" then the
+#       value is in megabytes.
+#
+. ./common/preamble
+_begin_fstest auto
+
+test_file="${TEST_DIR}/${seq}"
+seq=`basename $0`
+seqres="${RESULT_DIR}/${seq}"
+
+# Override the default cleanup function.
+_cleanup()
+{
+	cd /
+	rm -f "$test_file"
+}
+
+# Parse a size string which is in the format "XX.XXMib".
+#
+# Parameters:
+#   - (IN)    Block group type (Data, Metadata, System)
+#   - (INOUT) Variable to store block group size in MB
+#
+_parse_size_string() {
+	local SIZE=$(echo "$1" | awk 'match($0, /([0-9.]+)/) { print substr($0, RSTART, RLENGTH) }')
+        eval $2="${SIZE%.*}"
+}
+
+# Determine the size of the device in MB.
+#
+# Parameters:
+#   - (INOUT) Variable to store device size in MB
+#
+_device_size() {
+	btrfs fi show ${SCRATCH_MNT} --mbytes | grep devid >> $seqres.full
+	local SIZE=$(btrfs fi show ${SCRATCH_MNT} --mbytes | grep devid)
+	_parse_size_string $(echo "${SIZE}" | awk '{print $4}') SIZE_ALLOC
+	eval $1=${SIZE_ALLOC%.*}
+}
+
+# Determine the free space of a block group in MB.
+#
+# Parameters:
+#   - (INOUT) Variable to store free space in MB
+#
+_free_space() {
+	local SIZE=$(btrfs fi show ${SCRATCH_MNT} --mbytes | grep devid)
+	_parse_size_string $(echo "${SIZE}" | awk '{print $4}') SIZE_ALLOC
+	_parse_size_string $(echo "${SIZE}" | awk '{print $6}') SIZE_USED
+	eval $1=$(expr ${SIZE_ALLOC} - ${SIZE_USED})
+}
+
+# Determine how much space in MB has been allocated to a block group.
+#
+# Parameters:
+#   - (IN)    Block group type (Data, Metadata, System)
+#   - (INOUT) Variable to store block group size in MB
+#
+_alloc_size() {
+	local SIZE_STRING=$(btrfs filesystem df ${SCRATCH_MNT} -m | grep  "$1" | awk '{print $3}')
+	_parse_size_string ${SIZE_STRING} BLOCK_GROUP_SIZE
+        eval $2="${BLOCK_GROUP_SIZE}"
+}
+
+. ./common/filter
+_supported_fs btrfs
+_require_test
+_require_scratch
+_require_btrfs_fs_sysfs
+
+# Delete log file if it exists.
+rm -f "${seqres}.full"
+
+# Make filesystem.
+_require_scratch_size $((10 * 1024 * 1024)) #kB
+_scratch_mkfs_sized $((10 * 1024 * 1024 * 1024)) >> $seqres.full 2>&1
+_scratch_mount >> $seqres.full 2>&1
+
+# Get UUID of device.
+UUID="$(findmnt -n -o UUID ${SCRATCH_MNT})"
+echo "UUID = ${UUID}" >> ${seqres}.full
+

+
+#
+# Verification of initial allocation.
+#
+echo "Verify first allocation."
+FIRST_DATA_CHUNK_SIZE_MB=$(expr ${FIRST_DATA_CHUNK_SIZE_B} / 1024 / 1024)
+FIRST_METADATA_CHUNK_SIZE_MB=$(expr ${FIRST_METADATA_CHUNK_SIZE_B} / 1024 / 1024)
+
+# if [[ $(expr ${FIRST_DATA_CHUNK_SIZE_MB} + ${DATA_SIZE_START_MB}) -ne $(expr ${FIRST_DATA_SIZE_MB}) ]]; then
+if [[ $(expr ${FIRST_DATA_CHUNK_SIZE_MB} + ${DATA_SIZE_START_MB}) -ne ${FIRST_DATA_SIZE_MB} ]]; then
+	_fail "tInitial data allocation not correct."
+fi
+
+if [[ $(expr ${FIRST_METADATA_CHUNK_SIZE_MB} + ${METADATA_SIZE_START_MB}) -ne ${FIRST_METADATA_SIZE_MB} ]]; then
+	_fail "Initial metadata allocation not correct."
+fi
+
+#
+# Verification of second allocation.
+#
+echo "Verify second allocation."
+SECOND_DATA_CHUNK_SIZE_MB=$(expr ${SECOND_DATA_CHUNK_SIZE_B} / 1024 / 1024)
+SECOND_METADATA_CHUNK_SIZE_MB=$(expr ${SECOND_METADATA_CHUNK_SIZE_B} / 1024 / 1024)
+
+if [[ ${SECOND_DATA_CHUNK_SIZE_B} -ne ${SECOND_DATA_CHUNK_SIZE_READ_B} ]]; then
+	_fail "Value written to allocation/data/chunk_size and read value are different."
+fi
+
+if [[ ${SECOND_METADATA_CHUNK_SIZE_B} -ne ${SECOND_METADATA_CHUNK_SIZE_READ_B} ]]; then
+	_fail "Value written to allocation/metadata/chunk_size and read value are different."
+fi
+
+if [[ $(expr ${SECOND_DATA_CHUNK_SIZE_MB} + ${FIRST_DATA_SIZE_MB}) -ne ${SECOND_DATA_SIZE_MB} ]]; then
+	_fail "Data allocation after chunk size change not correct."
+fi
+
+if [[ $(expr ${SECOND_METADATA_CHUNK_SIZE_MB} + ${FIRST_METADATA_SIZE_MB}) -ne ${SECOND_METADATA_SIZE_MB} ]]; then
+	_fail "Metadata allocation after chunk size change not correct."
+fi
+
+#
+# Verification of third allocation.
+#
+echo "Verify third allocation."
+if [[ ${FREE_SPACE_MB} -gt ${THIRD_DATA_CHUNK_SIZE_MB} ]]; then
+	_fail "Free space after allocating over memlimit is too high."
+fi
+
+# The + 1 is required as 1MB is always kept as free space.
+if [[ $(expr ${THIRD_DATA_CHUNK_SIZE_MB} + ${THIRD_DATA_SIZE_MB} + 1) -le $(expr ${FOURTH_DATA_SIZE_MB}) ]]; then
+	_fail "Allocation until out of memory: last memory allocation size is not correct."
+fi
+
+status=0
+exit
+

diff --git a/tests/btrfs/248.out b/tests/btrfs/248.out
new file mode 100644
index 00000000..cac054a6
--- /dev/null
+++ b/tests/btrfs/248.out

@@ -0,0 +1,12 @@
+QA output created by 248
+Capture default chunk sizes.
+First allocation.
+Second allocation.
+Calculate request size so last memory allocation cannot be completely fullfilled.
+Third allocation.
+Force allocation of system block type must fail.
+_set_btrfs_sysfs_attr cannot write allocation/system/force_chunk_alloc
+(see /root/xfstests/results//btrfs/248.full for details)