Date:   Thu, 1 Mar 2018 14:17:17 -0700
From:   Andreas Dilger <adilger@...ger.ca>
To:     "Darrick J. Wong" <darrick.wong@...cle.com>
Cc:     tytso@....edu, djwong@...nel.org, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 1/7] e2scrub: create online fsck tool of sorts

On Mar 1, 2018, at 11:23 AM, Darrick J. Wong <darrick.wong@...cle.com> wrote:
> 
> From: Darrick J. Wong <darrick.wong@...cle.com>
> 
> Implement online fsck for ext* filesystems which live on LVM-managed
> logical volumes.  The basic strategy mirrors that of e2croncheck --
> create a snapshot, fsck the snapshot, report whatever errors appear,
> remove snapshot.  Unlike e2croncheck, this utility accepts any LVM
> device path, knows about snapshots running out of space, and can call
> fstrim having validated that the fs metadata is ok.

One high-level note - in my lvcheck script, there was an option to disable
background checking if the system was running on a battery:

# determine whether the machine is on AC power
function on_ac_power() {
        local any_known=no

        # try sysfs power class first
        if [ -d /sys/class/power_supply ]; then
                for psu in /sys/class/power_supply/*; do
                        if [ -r "$psu/type" ]; then
                                type=$(cat "$psu/type")

                                # ignore batteries
                                [ "$type" = "Battery" ] && continue

                                online=$(cat "$psu/online")

                                [ "$online" = 1 ] && return 0
                                [ "$online" = 0 ] && any_known=yes
                        fi
                done

                [ "$any_known" = "yes" ] && return 1
        fi

        # else fall back to AC adapters in /proc
        if [ -d /proc/acpi/ac_adapter ]; then
                for ac in /proc/acpi/ac_adapter/*; do
                        if [ -r "$ac/state" ]; then
                                grep -q on-line "$ac/state" && return 0
                                grep -q off-line "$ac/state" && any_known=yes
                        elif [ -r "$ac/status" ]; then
                                grep -q on-line "$ac/status" && return 0
                                grep -q off-line "$ac/status" && any_known=yes
                        fi
                done

                [ "$any_known" = "yes" ] && return 1
        fi

        if [ "$AC_UNKNOWN" == "CONTINUE" ]; then
                return 0        # assume on AC power
        elif [ "$AC_UNKNOWN" == "ABORT" ]; then
                return 1        # assume on battery
        else
                log err "Invalid value for AC_UNKNOWN in the config file"
                exit 1
        fi
}

More comments inline below.

> diff --git a/scrub/e2scrub.in b/scrub/e2scrub.in
> new file mode 100644
> index 0000000..32d11c8
> --- /dev/null
> +++ b/scrub/e2scrub.in
> @@ -0,0 +1,182 @@
> +#!/bin/bash
> +
> +#  Copyright (C) 2018 Oracle.  All Rights Reserved.
> +#
> +#  Author: Darrick J. Wong <darrick.wong@...cle.com>
> +#
> +#  This program is free software; you can redistribute it and/or
> +#  modify it under the terms of the GNU General Public License
> +#  as published by the Free Software Foundation; either version 2
> +#  of the License, or (at your option) any later version.
> +#
> +#  This program is distributed in the hope that it would be useful,
> +#  but WITHOUT ANY WARRANTY; without even the implied warranty of
> +#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> +#  GNU General Public License for more details.
> +#
> +#  You should have received a copy of the GNU General Public License
> +#  along with this program; if not, write the Free Software Foundation,
> +#  Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301, USA.
> +
> +# Automatically check a LVM-managed filesystem online.
> +# We use lvm snapshots to do this, which means that we can only
> +# check filesystems in VGs that have at least 256mb (or so) of
> +# free space.
> +
> +snap_size_mb=256
> +fstrim=0
> +e2fsck_opts=""
> +conffile="@root_sysconfdir@...scrub.conf"
> +
> +test -f "${conffile}" && . "${conffile}"
> +
> +print_help() {
> +	echo "Usage: $0 [-t] device"
> +	echo
> +	echo "device must be a LVM-managed block device"
> +	echo "-t: Run fstrim if successful."
> +}
> +
> +exitcode() {
> +	ret="$1"
> +
> +	exit "${ret}"
> +}
> +
> +prog_path() {
> +	path="$1"
> +	displayname="$2"
> +
> +	if ! type -P "${path}" && [ -n "${displayname}" ]; then
> +		echo "${displayname}: Command not found."
> +		exitcode 8
> +	fi
> +}
> +
> +LVS_PROG="$(prog_path "@root_sbindir@...s" "lvs")"
> +BLKID_PROG="$(prog_path "@root_sbindir@...kid" "blkid")"
> +LVCREATE_PROG="$(prog_path "@root_sbindir@...create" "lvcreate")"
> +LVREMOVE_PROG="$(prog_path "@root_sbindir@...remove" "lvremove")"
> +FSTRIM_PROG="$(prog_path "@root_sbindir@...trim")"
> +UDEVADM_PROG="$(prog_path "@root_sbindir@...evadm")"
> +SLEEP_PROG="$(prog_path "@root_bindir@...eep")"

Rather than hard-coding the pathnames for all of these commands, it would be
a lot easier to just use them by name and set an explicit PATH= to find them.
That avoids the need to do all of the substitutions, and makes the script
much less ugly.

> +while getopts "t" opt; do
> +	case "${opt}" in
> +	"t") fstrim=1;;
> +	*) print_help; exitcode 2;;
> +	esac
> +done
> +shift "$((OPTIND - 1))"
> +
> +dev="$1"
> +if [ -z "${dev}" ]; then
> +	print_help
> +	exitcode 1
> +elif [ ! -b "${dev}" ]; then
> +	echo "${dev}: Not a block device?"
> +	print_help
> +	exitcode 16
> +fi
> +
> +# Make sure this is an LVM device we can snapshot
> +vg="$("${LVS_PROG}" --noheadings -o vg_name "${dev}" 2> /dev/null | sed -e 's/^  //g')"
> +lv="$("${LVS_PROG}" --noheadings -o lv_name "${dev}" 2> /dev/null | sed -e 's/^  //g')"
> +if [ -z "${vg}" ] || [ -z "${lv}" ]; then
> +	echo "${dev}: Not a LVM device."
> +	exitcode 16
> +fi
> +start_time="$(date +'%Y%m%d%H%M%S')"
> +snap="${lv}.e2scrub"
> +snap_dev="/dev/${vg}/${snap}"
> +fstype="$("${BLKID_PROG}" -p -s TYPE "${dev}" | sed -e 's/^.*TYPE="\(.*\)".*$/\1/g')"
> +
> +case "${fstype}" in
> +"ext2"|"ext3"|"ext4")
> +	;;
> +*)
> +	echo "${dev}: Filesystem of type ${fstype} not supported."
> +	exitcode 16
> +	;;
> +esac
> +
> +teardown() {
> +	# Remove and wait for removal to succeed.
> +	"${LVREMOVE_PROG}" -f "${vg}/${snap}" 3>&-
> +	while [ -b "${snap_dev}" ] && [ "$?" -eq "5" ]; do
> +		/bin/sleep 0.5
> +		"${LVREMOVE_PROG}" -f "${vg}/${snap}" 3>&-
> +	done
> +}
> +
> +check() {
> +	# First we preen the filesystem to recover the journal, then
> +	# we see if e2fsck tries any non-optimization repairs.  If
> +	# either of these two returns a non-zero status (errors fixed
> +	# or remaining) then this fs is bad.
> +	E2FSCK_FIXES_ONLY=1
> +	export E2FSCK_FIXES_ONLY
> +	${DBG} "@root_sbindir@...fsck" -p ${e2fsck_opts} "${snap_dev}" || return 1
> +	${DBG} "@root_sbindir@...fsck" -fy ${e2fsck_opts} "${snap_dev}" || return

This could run two full e2fsck checks for each filesystem.  To recover only
the journal, it would be better to use "e2fsck -E journal_only"?

> +mark_corrupt() {
> +	${DBG} "@root_sbindir@...ne2fs" -C 16000 -T "19000101" "${dev}"

This won't actually do anything if the time/mount-based checks are disabled
(which has been the default for a long time already, not that I agree with it).
You need to add something like "-i 720" to force a check on the filesystem on
the next mount.

Also, this clobbers the mount count unnecessarily.

Finally, using "19000101" has the possibility to underflow in a different
timezone, and is a negative signed timestamp as well (but is stored as unsigned
value) so it may be problematic.

Better to use "19700102" or similar, which is just as likely to cause a check.

> +}
> +
> +setup() {
> +	# Create the snapshot, wait for device to appear
> +	teardown > /dev/null 2> /dev/null
> +	"${LVCREATE_PROG}" -s -L "${snap_size_mb}m" -n "${snap}" "${vg}/${lv}" 3>&-
> +	test $? -ne 0 && return 1
> +	test -x "${UDEVADM_PROG}" && "${UDEVADM_PROG}" settle
> +	return 0
> +}
> +
> +trap "teardown" EXIT INT QUIT TERM
> +if ! setup; then
> +	echo "Snapshot of ${dev} FAILED, will not check!"
> +	exitcode 1
> +fi
> +
> +# Check and react
> +if check; then
> +	echo "Scrub of ${dev} succeeded."
> +	mark_clean
> +
> +	if [ "${fstrim}" -eq 1 ] && [ -x "${FSTRIM_PROG}" ]; then
> +		dir="$(lsblk -o MOUNTPOINT -n "${dev}")"
> +		if [ -d "${dir}" ]; then
> +			# NB: fstrim fails with snapshot present
> +			trap '' EXIT
> +			teardown
> +			"${FSTRIM_PROG}" -v "${dir}"
> +		fi
> +	fi
> +
> +	ret=0
> +else
> +	# fsck failed.  Check if the snapshot is invalid; if so, make a
> +	# note of that at the end of the log.  This isn't necessarily a
> +	# failure because the mounted fs could have overflowed the
> +	# snapshot with regular disk writes /or/ our repair process
> +	# could have done it by repairing too much.
> +	#
> +	# If it's really corrupt we ought to fsck at next boot.
> +	is_invalid="$("${LVS_PROG}" -o lv_snapshot_invalid --noheadings "${snap_dev}")"
> +	if [ -n "${is_invalid}" ]; then
> +		echo "Scrub of ${dev} FAILED due to invalid snapshot."
> +		ret=8
> +	else
> +		echo "Scrub of ${dev} FAILED!  Reboot soon to fsck."
> +		mark_corrupt
> +		ret=6
> +	fi
> +fi
> +
> +exitcode "${ret}"


Cheers, Andreas






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