linux-ext4 - [PATCH 1/2] e2scrub_all: don't even reap if the config file doesn't allow it

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Date:   Mon, 04 Nov 2019 17:54:14 -0800
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     tytso@....edu, darrick.wong@...cle.com
Cc:     linux-ext4@...r.kernel.org, Dave Chinner <david@...morbit.com>
Subject: [PATCH 1/2] e2scrub_all: don't even reap if the config file doesn't
 allow it

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

Dave Chinner complains that the automated on-boot e2scrub reaping takes
a long time (because the lvs command can take a while to run) even
though the automated e2scrub is disabled via e2scrub.conf on his
systems.

We still need the reaping service to kill off stale e2scrub snapshots
after a crash, but it's unnecessary to annoy everyone with slow bootup.
Because we can look for the e2scrub snapshots in /dev/mapper, let's
skip reaping if periodic e2scrub is disabled unless we find evidence of
e2scrub snapshots in /dev.

Reported-by: Dave Chinner <david@...morbit.com>
Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
---
 scrub/e2scrub_all.in |   15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/scrub/e2scrub_all.in b/scrub/e2scrub_all.in
index 1418a229..72e66ff6 100644
--- a/scrub/e2scrub_all.in
+++ b/scrub/e2scrub_all.in
@@ -80,9 +80,18 @@ while getopts "nrAV" opt; do
 done
 shift "$((OPTIND - 1))"

-if [ -n "${SERVICE_MODE}" -a "${reap}" -ne 1 -a "${periodic_e2scrub}" -ne 1 ]
-then
-    exitcode 0
+# If we're in service mode and the service is not enabled via config file...
+if [ -n "${SERVICE_MODE}" -a "${periodic_e2scrub}" -ne 1 ]; then
+	# ...don't start e2scrub processes.
+	if [ "${reap}" -eq 0 ]; then
+		exitcode 0
+	fi
+
+	# ...and if we don't see any leftover e2scrub snapshots, don't
+	# run the reaping process either, because lvs can be slow.
+	if ! readlink -q -s -e /dev/mapper/*.e2scrub* > /dev/null; then
+		exitcode 0
+	fi
 fi

 # close file descriptor 3 (from cron) since it causes lvm to kvetch