diff --git a/common/rc b/common/rc
index 0a30a842..bdd29b06 100644
--- a/common/rc
+++ b/common/rc
@@ -4401,7 +4401,14 @@ run_fsx()
 _require_fs_sysfs()
 {
 	local attr=$1
-	local dname=$(_short_dev $TEST_DEV)
+	local dname
+
+	case "$FSTYP" in
+	btrfs)
+		dname=$(findmnt -n -o UUID $TEST_DEV) ;;
+	*)
+		dname=$(_short_dev $TEST_DEV) ;;
+	esac
 
 	if [ -z "$attr" -o -z "$dname" ];then
 		_fail "Usage: _require_fs_sysfs <sysfs_attr_path>"
@@ -4439,7 +4446,14 @@ _set_fs_sysfs_attr()
 		_fail "Usage: _set_fs_sysfs_attr <mounted_device> <attr> <content>"
 	fi
 
-	local dname=$(_short_dev $dev)
+	local dname
+	case "$FSTYP" in
+	btrfs)
+		dname=$(findmnt -n -o UUID ${dev}) ;;
+	*)
+		dname=$(_short_dev $dev) ;;
+	esac
+
 	echo "$content" > /sys/fs/${FSTYP}/${dname}/${attr}
 }
 
@@ -4460,7 +4474,14 @@ _get_fs_sysfs_attr()
 		_fail "Usage: _get_fs_sysfs_attr <mounted_device> <attr>"
 	fi
 
-	local dname=$(_short_dev $dev)
+	local dname
+	case "$FSTYP" in
+	btrfs)
+		dname=$(findmnt -n -o UUID ${dev}) ;;
+	*)
+		dname=$(_short_dev $dev) ;;
+	esac
+
 	cat /sys/fs/${FSTYP}/${dname}/${attr}
 }
 
diff --git a/tests/btrfs/251 b/tests/btrfs/251
new file mode 100755
index 00000000..11925f5b
--- /dev/null
+++ b/tests/btrfs/251
@@ -0,0 +1,285 @@
+#!/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
+
+seq=`basename $0`
+seqres="${RESULT_DIR}/${seq}"
+
+# Override the default cleanup function.
+_cleanup()
+{
+	cd /
+}
+
+# Parse a size string which is in the format "XX.XXMib".
+#
+# Parameters:
+#   - (IN)    Block group type (Data, Metadata, System)
+#   - (INOUT) Variable to store block group size in MB
+#
+parse_size_string() {
+	local SIZE=$(echo "$1" | $AWK_PROG '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_UTIL_PROG filesystem 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_UTIL_PROG filesystem 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_UTIL_PROG 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
+
+# Delete log file if it exists.
+rm -f "${seqres}.full"
+
+# Make filesystem. 10GB is needed to have sufficient space for testing
+# block types and chunk sizes.
+_scratch_mkfs_sized $((10 * 1024 * 1024 * 1024)) >> $seqres.full 2>&1
+_scratch_mount >> $seqres.full 2>&1
+
+# Check if there is sufficient sysfs support.
+_require_fs_sysfs allocation/metadata/chunk_size
+_require_fs_sysfs allocation/metadata/force_chunk_alloc
+
+# Get free space.
+free_space  FREE_SPACE_MB
+device_size DEVICE_SIZE_MB
+
+echo "free space = ${FREE_SPACE_MB}MB" >> ${seqres}.full
+
+# If device is a symbolic link, get block device.
+SCRATCH_BDEV=${SCRATCH_DEV}
+if [[ -h ${SCRATCH_DEV} ]]; then
+	SCRATCH_BDEV=$(readlink -f $SCRATCH_DEV)
+fi
+
+# Get chunk sizes.
+echo "Capture default chunk sizes."
+FIRST_DATA_CHUNK_SIZE_B=$(_get_fs_sysfs_attr ${SCRATCH_BDEV} allocation/data/chunk_size)
+FIRST_METADATA_CHUNK_SIZE_B=$(_get_fs_sysfs_attr ${SCRATCH_BDEV} allocation/metadata/chunk_size)
+
+echo "Orig Data chunk size    = ${FIRST_DATA_CHUNK_SIZE_B}"     >> ${seqres}.full
+echo "Orig Metaata chunk size = ${FIRST_METADATA_CHUNK_SIZE_B}" >> ${seqres}.full
+
+INIT_ALLOC_SIZE_MB=$(expr \( ${FIRST_DATA_CHUNK_SIZE_B} + ${FIRST_METADATA_CHUNK_SIZE_B} \) / 1024 / 1024)
+echo "Allocation size for initial allocation = ${INIT_ALLOC_SIZE_MB}MB" >> $seqres.full
+
+#
+# Do first allocation with the default chunk sizes for the different block
+# types.
+#
+echo "First allocation."
+alloc_size "Data"     DATA_SIZE_START_MB
+alloc_size "Metadata" METADATA_SIZE_START_MB
+
+echo "Block group Data alloc size     = ${DATA_SIZE_START_MB}MB"     >> $seqres.full
+echo "Block group Metadata alloc size = ${METADATA_SIZE_START_MB}MB" >> $seqres.full
+
+_set_fs_sysfs_attr ${SCRATCH_BDEV} allocation/data/force_chunk_alloc 1
+_set_fs_sysfs_attr ${SCRATCH_BDEV} allocation/metadata/force_chunk_alloc 1
+
+alloc_size "Data"     FIRST_DATA_SIZE_MB
+alloc_size "Metadata" FIRST_METADATA_SIZE_MB
+
+echo "First block group Data alloc size     = ${FIRST_DATA_SIZE_MB}MB"     >> ${seqres}.full
+echo "First block group Metadata alloc size = ${FIRST_METADATA_SIZE_MB}MB" >> ${seqres}.full
+
+free_space FREE_SPACE_AFTER
+echo "Free space after first allocation = ${FREE_SPACE_AFTER}MB" >> ${seqres}.full
+
+#
+# Do allocation with the doubled chunk sizes for the different block types.
+#
+echo "Second allocation."
+SECOND_DATA_CHUNK_SIZE_B=$(expr ${FIRST_DATA_CHUNK_SIZE_B} \* 2)
+SECOND_METADATA_CHUNK_SIZE_B=$(expr ${FIRST_METADATA_CHUNK_SIZE_B} \* 2)
+
+echo "Second block group Data calc alloc size     = ${SECOND_DATA_CHUNK_SIZE_B}"     >> $seqres.full
+echo "Second block group Metadata calc alloc size = ${SECOND_METADATA_CHUNK_SIZE_B}" >> $seqres.full
+
+# Stripe size is limited to 10% of device size.
+if [[ ${SECOND_DATA_CHUNK_SIZE_B} -gt $(expr ${DEVICE_SIZE_MB} \* 10 \* 1024 \* 1024 / 100) ]]; then
+	SECOND_DATA_CHUNK_SIZE_B=$(expr ${DEVICE_SIZE_MB} \* 10 / 100 \* 1024 \* 1024)
+fi
+if [[ ${SECOND_METADATA_CHUNK_SIZE_B} -gt $(expr ${DEVICE_SIZE_MB} \* 10 \* 1024 \* 1024 / 100) ]]; then
+	SECOND_METADATA_CHUNK_SIZE_B=$(expr ${DEVICE_SIZE_MB} \* 10 / 100 \* 1024 \* 1024)
+fi
+
+echo "Second block group Data alloc size     = ${SECOND_DATA_CHUNK_SIZE_B}"     >> $seqres.full
+echo "Second block group Metadata alloc size = ${SECOND_METADATA_CHUNK_SIZE_B}" >> $seqres.full
+
+_set_fs_sysfs_attr ${SCRATCH_BDEV} allocation/data/chunk_size ${SECOND_DATA_CHUNK_SIZE_B}
+_set_fs_sysfs_attr ${SCRATCH_BDEV} allocation/metadata/chunk_size ${SECOND_METADATA_CHUNK_SIZE_B}
+
+SECOND_DATA_CHUNK_SIZE_READ_B=$(_get_fs_sysfs_attr ${SCRATCH_BDEV} allocation/data/chunk_size)
+SECOND_METADATA_CHUNK_SIZE_READ_B=$(_get_fs_sysfs_attr ${SCRATCH_BDEV} allocation/metadata/chunk_size)
+
+_set_fs_sysfs_attr ${SCRATCH_BDEV} allocation/data/force_chunk_alloc 1
+echo "Allocated data chunk" >> $seqres.full
+_set_fs_sysfs_attr ${SCRATCH_BDEV} allocation/metadata/force_chunk_alloc 1
+echo "Allocated metadata chunk" >> $seqres.full
+
+alloc_size "Data"     SECOND_DATA_SIZE_MB
+alloc_size "Metadata" SECOND_METADATA_SIZE_MB
+alloc_size "System"   SECOND_SYSTEM_SIZE_MB
+
+echo "Calculate request size so last memory allocation cannot be completely fullfilled."
+free_space FREE_SPACE_MB
+
+# Find request size whose space allocation cannot be completely fullfilled.
+THIRD_DATA_CHUNK_SIZE_MB=$(expr 256)
+until [ ${THIRD_DATA_CHUNK_SIZE_MB} -gt $(expr 7 \* 1024) ]; do
+	if [ $((FREE_SPACE_MB%THIRD_DATA_CHUNK_SIZE_MB)) -ne 0 ]; then
+		break
+        fi
+	THIRD_DATA_CHUNK_SIZE_MB=$((THIRD_DATA_CHUNK_SIZE_MB+256))
+done
+
+if [[ ${THIRD_DATA_CHUNK_SIZE_MB} -eq $(expr 7 \* 1024) ]]; then
+	_fail "Cannot find allocation size for partial block allocation."
+fi
+
+THIRD_DATA_CHUNK_SIZE_B=$(expr ${THIRD_DATA_CHUNK_SIZE_MB} \* 1024 \* 1024)
+echo "Allocation size in mb    = ${THIRD_DATA_CHUNK_SIZE_MB}" >> ${seqres}.full
+echo "Allocation size in bytes = ${THIRD_DATA_CHUNK_SIZE_B}"  >> ${seqres}.full
+
+#
+# Do allocation until free space is exhausted.
+#
+echo "Third allocation."
+_set_fs_sysfs_attr ${SCRATCH_BDEV} allocation/data/chunk_size ${THIRD_DATA_CHUNK_SIZE_B}
+
+free_space FREE_SPACE_MB
+while [ $FREE_SPACE_MB -gt $THIRD_DATA_CHUNK_SIZE_MB ]
+do
+	alloc_size "Data" THIRD_DATA_SIZE_MB
+	_set_fs_sysfs_attr ${SCRATCH_BDEV} allocation/data/force_chunk_alloc 1
+
+	free_space FREE_SPACE_MB
+done
+
+alloc_size "Data" FOURTH_DATA_SIZE_MB
+
+#
+# Force chunk allocation of system block type must fail.
+#
+echo "Force allocation of system block type must fail."
+_set_fs_sysfs_attr ${SCRATCH_BDEV} allocation/system/force_chunk_alloc 1 2>/dev/null
+if [ $? -ne 0 ]; then
+	_dump_err "_set_fs_sysfs_attr cannot write allocation/system/force_chunk_alloc"
+fi
+
+#
+# Verification of initial allocation.
+#
+echo "Verify first allocation."
+FIRST_DATA_CHUNK_SIZE_MB=$(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
+	echo "tInitial data allocation not correct."
+fi
+
+if [[ $(expr ${FIRST_METADATA_CHUNK_SIZE_MB} + ${METADATA_SIZE_START_MB}) -ne ${FIRST_METADATA_SIZE_MB} ]]; then
+	echo "Initial metadata allocation not correct."
+fi
+
+#
+# Verification of second allocation.
+#
+echo "Verify second allocation."
+SECOND_DATA_CHUNK_SIZE_MB=$(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
+	echo "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
+	echo "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
+	echo "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
+	echo "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
+	echo "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
+	echo "Allocation until out of memory: last memory allocation size is not correct."
+fi
+
+status=0
+exit
+
diff --git a/tests/btrfs/251.out b/tests/btrfs/251.out
new file mode 100644
index 00000000..f5e16ee8
--- /dev/null
+++ b/tests/btrfs/251.out
@@ -0,0 +1,11 @@
+QA output created by 251
+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_fs_sysfs_attr cannot write allocation/system/force_chunk_alloc
+Verify first allocation.
+Verify second allocation.
+Verify third allocation.
