Add Linux posix_fadvise support

The purpose of this PR is to accepts fadvise ioctl from userland
to do read-ahead by demand.

It could dramatically improve sequential read performance especially
when primarycache is set to metadata or zfs_prefetch_disable is 1.

If the file is mmaped, generic_fadvise is also called for page cache
read-ahead besides dmu_prefetch.

Only POSIX_FADV_WILLNEED and POSIX_FADV_SEQUENTIAL are supported in
this PR currently.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Finix Yan <yancw@info2soft.com>
Closes #13694

tests/zfs-tests/tests/functional/fadvise/cleanup.ksh

@@ -0,0 +1,28 @@
+#!/bin/ksh -p
+#
+# CDDL HEADER START
+#
+# The contents of this file are subject to the terms of the
+# Common Development and Distribution License (the "License").
+# You may not use this file except in compliance with the License.
+#
+# You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+# or https://opensource.org/licenses/CDDL-1.0.
+# See the License for the specific language governing permissions
+# and limitations under the License.
+#
+# When distributing Covered Code, include this CDDL HEADER in each
+# file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+# If applicable, add the following below this CDDL HEADER, with the
+# fields enclosed by brackets "[]" replaced with your own identifying
+# information: Portions Copyright [yyyy] [name of copyright owner]
+#
+# CDDL HEADER END
+
+#
+# Portions Copyright (c) 2022 Information2 Software, Inc.
+#
+
+. $STF_SUITE/include/libtest.shlib
+
+default_cleanup

tests/zfs-tests/tests/functional/fadvise/fadvise_sequential.ksh

@@ -0,0 +1,80 @@
+#!/bin/ksh -p
+#
+# CDDL HEADER START
+#
+# The contents of this file are subject to the terms of the
+# Common Development and Distribution License (the "License").
+# You may not use this file except in compliance with the License.
+#
+# You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+# or https://opensource.org/licenses/CDDL-1.0.
+# See the License for the specific language governing permissions
+# and limitations under the License.
+#
+# When distributing Covered Code, include this CDDL HEADER in each
+# file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+# If applicable, add the following below this CDDL HEADER, with the
+# fields enclosed by brackets "[]" replaced with your own identifying
+# information: Portions Copyright [yyyy] [name of copyright owner]
+#
+# CDDL HEADER END
+#
+
+#
+# Portions Copyright (c) 2022 Information2 Software, Inc.
+#
+
+. $STF_SUITE/include/libtest.shlib
+. $STF_SUITE/include/math.shlib
+
+#
+# DESCRIPTION:
+# Test posix_fadvise.
+#
+# STRATEGY:
+# 1. Set primarycache to metadata in order to disable prefetch
+# 2. Write some data to file 
+# 3. get data_size field from arcstat
+# 4. call file_fadvise with POSIX_FADV_SEQUENTIAL
+# 5. get data_size field from arcstat again
+# 6. latter data_size should be bigger than former one
+#
+
+# NOTE: if HAVE_FILE_FADVISE is not defined former data_size
+# should less or eaqul to latter one
+
+verify_runnable "global"
+
+FILE=$TESTDIR/$TESTFILE0
+BLKSZ=$(get_prop recordsize $TESTPOOL)
+
+function cleanup
+{
+	log_must zfs set primarycache=all $TESTPOOL
+	[[ -e $TESTDIR ]] && log_must rm -Rf $TESTDIR/*
+}
+
+getstat() {
+	awk -v c="$1" '$1 == c {print $3; exit}' /proc/spl/kstat/zfs/arcstats
+}
+
+log_assert "Ensure fadvise prefetch data"
+
+log_onexit cleanup
+
+log_must zfs set primarycache=metadata $TESTPOOL
+
+log_must file_write -o create -f $FILE -b $BLKSZ -c 1000
+sync_pool $TESTPOOL
+
+data_size1=$(getstat data_size)
+
+log_must file_fadvise -f $FILE -a 2
+sleep 10
+
+data_size2=$(getstat data_size)
+log_note "original data_size is $data_size1, final data_size is $data_size2"
+
+log_must [ $data_size1 -le $data_size2 ]
+
+log_pass "Ensure data could be prefetched"

tests/zfs-tests/tests/functional/fadvise/setup.ksh

@@ -0,0 +1,30 @@
+#!/bin/ksh -p
+#
+# CDDL HEADER START
+#
+# The contents of this file are subject to the terms of the
+# Common Development and Distribution License (the "License").
+# You may not use this file except in compliance with the License.
+#
+# You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+# or https://opensource.org/licenses/CDDL-1.0.
+# See the License for the specific language governing permissions
+# and limitations under the License.
+#
+# When distributing Covered Code, include this CDDL HEADER in each
+# file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+# If applicable, add the following below this CDDL HEADER, with the
+# fields enclosed by brackets "[]" replaced with your own identifying
+# information: Portions Copyright [yyyy] [name of copyright owner]
+#
+# CDDL HEADER END
+
+#
+# Portions Copyright (c) 2022 Information2 Software, Inc.
+#
+
+. $STF_SUITE/include/libtest.shlib
+
+DISK=${DISKS%% *}
+default_setup_noexit $DISK
+log_pass