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Date:   Mon, 18 Mar 2019 17:17:32 -0700
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     "Theodore Ts'o" <tytso@....edu>
Cc:     linux-ext4@...r.kernel.org, Paul Menzel <pmenzel@...gen.mpg.de>
Subject: [PATCH] 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 T'so 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.

Reported-by: Paul Menzel <pmenzel@...gen.mpg.de>
Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
---
 scrub/e2scrub_all.in |   51 ++++++++++++++++++++++++++++++++++++--------------
 1 file changed, 37 insertions(+), 14 deletions(-)

diff --git a/scrub/e2scrub_all.in b/scrub/e2scrub_all.in
index 23d122d25..41420d03d 100644
--- a/scrub/e2scrub_all.in
+++ b/scrub/e2scrub_all.in
@@ -19,6 +19,7 @@
 #  Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301, USA.
 
 scrub_all=0
+reap=0
 conffile="@root_sysconfdir@...scrub.conf"
 
 test -f "${conffile}" && . "${conffile}"
@@ -61,7 +62,7 @@ exitcode() {
 while getopts "ArV" opt; do
 	case "${opt}" in
 	"A") scrub_all=1;;
-	"r") scrub_args="${scrub_args} -r";;
+	"r") scrub_args="${scrub_args} -r"; reap=1;;
 	"V") print_version; exitcode 0;;
 	*) print_help; exitcode 2;;
 	esac
@@ -69,27 +70,27 @@ done
 shift "$((OPTIND - 1))"
 
 # 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
+ls_scan_targets() {
+	lvs --name-prefixes -o vg_name,lv_name,lv_path \
+			-S lv_active=active,lv_role=public --noheadings | \
+	while read vars; do
 		eval "${vars}"
+		eval "$(lsblk -o NAME,FSTYPE,MOUNTPOINT -p -P -n "${LVM2_LV_PATH}")"
 
-		# Skip non-ext[234]
+		# Skip unless ext*
 		case "${FSTYPE}" in
-		ext[234])	;;
-		*)		continue;;
+		ext*) ;;
+		*) continue;;
 		esac
 
+		# Don't run against a snapshot ever
+		echo "${LVM2_LV_ROLE}" | grep -q "snapshot" && continue
+
 		# Skip unmounted filesystems unless -A
 		if [ "${scrub_all}" -eq 0 ] && [ -z "${MOUNTPOINT}" ]; then
 			continue;
 		fi
 
-		# 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 "${LVM2_LV_ROLE}" | grep -q "snapshot" && continue
-
 		if [ -n "${MOUNTPOINT}" ]; then
 			echo "${MOUNTPOINT}"
 		else
@@ -98,6 +99,28 @@ ls_scrub_targets() {
 	done | sort | uniq
 }
 
+# Find leftover scrub snapshots
+ls_reap_targets() {
+	lvs --name-prefixes -o vg_name,lv_name,lv_path,origin \
+		-S lv_role=snapshot --noheadings | while read vars; do
+		eval "${vars}"
+
+		# Filter out anything except our snapshots
+		case "${LVM2_LV_NAME}" in
+		*.e2scrub) echo "${LVM2_LV_PATH}";;
+		esac
+	done | sort | uniq
+}
+
+# Figure out what we're targeting
+ls_targets() {
+	if [ "${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
 # to the e2scrub service, which breaks things if there is a dash in the path
 # name.  Therefore, do the path escaping ourselves if needed.
@@ -118,10 +141,10 @@ 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=$?

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