linux-ext4 - [PATCH 8/9] e2scrub_all: refactor device probe loop

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Date:   Thu, 21 Mar 2019 16:25:12 -0400
From:   "Theodore Ts'o" <tytso@....edu>
To:     Ext4 Developers List <linux-ext4@...r.kernel.org>
Cc:     darrick.wong@...cle.com, lczerner@...hat.com,
        "Theodore Ts'o" <tytso@....edu>
Subject: [PATCH 8/9] e2scrub_all: refactor device probe loop

From: "Darrick J. Wong" <darrick.wong@...cle.com>

Paul Menzel reported that the e2scrub_all reaper service that runs at
startup takes a long time to run, and Ted Ts'o pointed out that we could
do a lot less work by using lvs as the outer loop in the ext4 filesystem
probe function so that we only have to lsblk the lvm devices containing
ext4 filesystems.

Therefore, refactor the loops to put lvs first, which should boost speed
a bit.

[ Made some of the further optimizations suggested by Lukas Czerner.  -- TYT ]

Reported-by: Paul Menzel <pmenzel@...gen.mpg.de>
Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
Signed-off-by: Theodore Ts'o <tytso@....edu>
---
 scrub/e2scrub_all.in | 49 ++++++++++++++++++++++----------------------
 1 file changed, 24 insertions(+), 25 deletions(-)

diff --git a/scrub/e2scrub_all.in b/scrub/e2scrub_all.in
index 4cb90a0de..81340b76f 100644
--- a/scrub/e2scrub_all.in
+++ b/scrub/e2scrub_all.in
@@ -22,6 +22,7 @@ PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
 
 scrub_all=0
 snap_size_mb=256
+reap=0
 conffile="@root_sysconfdir@...scrub.conf"
 
 test -f "${conffile}" && . "${conffile}"
@@ -65,7 +66,7 @@ exitcode() {
 while getopts "nrAV" opt; do
 	case "${opt}" in
 	"n") DBG="echo Would execute: " ;;
-	"r") scrub_args="${scrub_args} -r";;
+	"r") scrub_args="${scrub_args} -r"; reap=1;;
 	"A") scrub_all=1;;
 	"V") print_version; exitcode 0;;
 	*) print_help; exitcode 2;;
@@ -88,36 +89,34 @@ if ! type lvcreate >& /dev/null ; then
 fi
 
 # Find scrub targets, make sure we only do this once.
-ls_scrub_targets() {
-	lsblk -o NAME,FSTYPE,MOUNTPOINT -p -P -n | while read vars; do
-		eval "${vars}"
-
+ls_scan_targets() {
+	for NAME in $(lvs -o lv_path --noheadings \
+		   -S "lv_active=active,lv_role=public,lv_role!=snapshot,vg_free>${snap_size_mb}") ; do
 		# Skip non-ext[234]
-		case "${FSTYPE}" in
+		case "$(blkid -o value -s TYPE ${NAME})" in
 		ext[234])	;;
 		*)		continue;;
 		esac
 
-		# Skip unmounted filesystems unless -A
-		if [ "${scrub_all}" -eq 0 ] && [ -z "${MOUNTPOINT}" ]; then
-			continue;
+		if [ "${scrub_all}" -eq 1 ] ||
+		   [ -n "$(lsblk -o MOUNTPOINT --noheadings ${NAME})" ]; then
+		    echo ${NAME}
 		fi
+	done | sort | uniq
+}
 
-		# Skip non-lvm devices and lvm snapshots
-		lvm_vars="$(lvs --nameprefixes -o vg_name,lv_name,lv_role --noheadings "${NAME}" 2> /dev/null)"
-		test $? -ne 0 && continue
-		eval "${lvm_vars}"
-		echo "${LVM2_LV_ROLE}" | grep -q "snapshot" && continue
-
-		free_space="$(vgs -o vg_free --units m --noheadings --no-suffix "${LVM2_VG_NAME}" 2> /dev/null | sed -e 's/\..*//')"
-		test "${snap_size_mb}" -gt "${free_space}" && continue
+# Find leftover scrub snapshots
+ls_reap_targets() {
+	lvs -o lv_path -S lv_role=snapshot -S lv_name=~\(e2scrub$\) --noheadings
+}
 
-		if [ -n "${MOUNTPOINT}" ]; then
-			echo "${MOUNTPOINT}"
-		else
-			echo "${NAME}"
-		fi
-	done | sort | uniq
+# Figure out what we're targeting
+ls_targets() {
+	if [ "${reap}" -eq 1 ]; then
+		ls_reap_targets
+	else
+		ls_scan_targets
+	fi
 }
 
 # systemd doesn't know to do path escaping on the instance variable we pass
@@ -140,10 +139,10 @@ escape_path_for_systemd() {
 
 # Scrub any mounted fs on lvm by creating a snapshot and fscking that.
 stdin="$(realpath /dev/stdin)"
-ls_scrub_targets | while read tgt; do
+ls_targets | while read tgt; do
 	# If we're not reaping and systemd is present, try invoking the
 	# systemd service.
-	if [ -z "${scrub_args}" ] && type systemctl > /dev/null 2>&1; then
+	if [ "${reap}" -ne 1 ] && type systemctl > /dev/null 2>&1; then
 		tgt_esc="$(escape_path_for_systemd "${tgt}")"
 		${DBG} systemctl start "e2scrub@...gt_esc}" 2> /dev/null < "${stdin}"
 		res=$?
-- 
2.19.1