selftests/ublk: add filesystem fio verify test for shmem_zc

Add test_shmemzc_03.sh which exercises shmem_zc through the full
filesystem stack: mkfs ext4 on the ublk device, mount it, then run
fio verify on a file inside the filesystem with --mem=mmaphuge.

Extend _mkfs_mount_test() to accept an optional command that runs
between mount and umount. The function cd's into the mount directory
so the command can use relative file paths. Existing callers that
pass only the device are unaffected.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://patch.msgid.link/20260331153207.3635125-10-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: Ming Lei

tools/testing/selftests/ublk/Makefile

@@ -54,6 +54,7 @@ TEST_PROGS += test_part_02.sh
 
 TEST_PROGS += test_shmemzc_01.sh
 TEST_PROGS += test_shmemzc_02.sh
+TEST_PROGS += test_shmemzc_03.sh
 
 TEST_PROGS += test_stress_01.sh
 TEST_PROGS += test_stress_02.sh

tools/testing/selftests/ublk/test_common.sh

@@ -88,6 +88,7 @@ _remove_tmp_dir() {
 _mkfs_mount_test()
 {
 	local dev=$1
+	shift
 	local err_code=0
 	local mnt_dir;
 
@@ -99,12 +100,17 @@ _mkfs_mount_test()
 	fi
 
 	mount -t ext4 "$dev" "$mnt_dir" > /dev/null 2>&1
+	if [ $# -gt 0 ]; then
+		cd "$mnt_dir" && "$@"
+		err_code=$?
+		cd - > /dev/null
+	fi
 	umount "$dev"
-	err_code=$?
-	_remove_tmp_dir "$mnt_dir"
-	if [ $err_code -ne 0 ]; then
-		return $err_code
+	if [ $err_code -eq 0 ]; then
+		err_code=$?
 	fi
+	_remove_tmp_dir "$mnt_dir"
+	return $err_code
 }
 
 _check_root() {
@@ -132,6 +138,7 @@ _prep_test() {
 	local base_dir=${TMPDIR:-./ublktest-dir}
 	mkdir -p "$base_dir"
 	UBLK_TEST_DIR=$(mktemp -d ${base_dir}/${TID}.XXXXXX)
+	UBLK_TEST_DIR=$(realpath ${UBLK_TEST_DIR})
 	UBLK_TMP=$(mktemp ${UBLK_TEST_DIR}/ublk_test_XXXXX)
 	[ "$UBLK_TEST_QUIET" -eq 0 ] && echo "ublk $type: $*"
 	echo "ublk selftest: $TID starting at $(date '+%F %T')" | tee /dev/kmsg

tools/testing/selftests/ublk/test_shmemzc_03.sh

@@ -0,0 +1,69 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Test: shmem_zc with fio verify over filesystem on loop target
+#
+# mkfs + mount ext4 on the ublk device, then run fio verify on a
+# file inside that filesystem.  Exercises the full stack:
+# filesystem -> block layer -> ublk shmem_zc -> loop target backing file.
+
+. "$(cd "$(dirname "$0")" && pwd)"/test_common.sh
+
+ERR_CODE=0
+
+_prep_test "shmem_zc" "loop target hugetlbfs shmem zero-copy fs verify test"
+
+if ! _have_program fio; then
+	echo "SKIP: fio not available"
+	exit "$UBLK_SKIP_CODE"
+fi
+
+if ! grep -q hugetlbfs /proc/filesystems; then
+	echo "SKIP: hugetlbfs not supported"
+	exit "$UBLK_SKIP_CODE"
+fi
+
+# Allocate hugepages
+OLD_NR_HP=$(cat /proc/sys/vm/nr_hugepages)
+echo 10 > /proc/sys/vm/nr_hugepages
+NR_HP=$(cat /proc/sys/vm/nr_hugepages)
+if [ "$NR_HP" -lt 2 ]; then
+	echo "SKIP: cannot allocate hugepages"
+	echo "$OLD_NR_HP" > /proc/sys/vm/nr_hugepages
+	exit "$UBLK_SKIP_CODE"
+fi
+
+# Mount hugetlbfs
+HTLB_MNT=$(mktemp -d "${UBLK_TEST_DIR}/htlb_mnt_XXXXXX")
+if ! mount -t hugetlbfs none "$HTLB_MNT"; then
+	echo "SKIP: cannot mount hugetlbfs"
+	rmdir "$HTLB_MNT"
+	echo "$OLD_NR_HP" > /proc/sys/vm/nr_hugepages
+	exit "$UBLK_SKIP_CODE"
+fi
+
+HTLB_FILE="$HTLB_MNT/ublk_buf"
+fallocate -l 4M "$HTLB_FILE"
+
+_create_backfile 0 256M
+BACKFILE="${UBLK_BACKFILES[0]}"
+
+dev_id=$(_add_ublk_dev -t loop --shmem_zc --htlb "$HTLB_FILE" "$BACKFILE")
+_check_add_dev $TID $?
+
+_mkfs_mount_test /dev/ublkb"${dev_id}" \
+	_run_fio_verify_io --filename=testfile \
+		--size=128M \
+		--mem=mmaphuge:"$HTLB_FILE"
+ERR_CODE=$?
+
+# Delete device first so daemon releases the htlb mmap
+_ublk_del_dev "${dev_id}"
+
+rm -f "$HTLB_FILE"
+umount "$HTLB_MNT"
+rmdir "$HTLB_MNT"
+echo "$OLD_NR_HP" > /proc/sys/vm/nr_hugepages
+
+_cleanup_test "shmem_zc"
+
+_show_result $TID $ERR_CODE