Revert "Changed (and simplified) DST handling (see here: https://github.com/jimsalterjrs/sanoid/issues/155)"

This reverts commit cf496dcf86.

README.md

@@ -9,7 +9,7 @@ More prosaically, you can use Sanoid to create, automatically thin, and monitor
 * * * * * TZ=UTC /usr/local/bin/sanoid --cron
 ```
 
-**`IMPORTANT NOTE`**: using a local timezone will result in a single hourly snapshot to be **skipped** during `daylight->nodaylight` transition. To avoid that, using UTC as timezone is recommend whenever possible.
+`Note`: Using UTC as timezone is recommend to prevent problems with daylight saving times
 
 And its /etc/sanoid/sanoid.conf might look something like this:
 

sanoid

@@ -357,6 +357,19 @@ sub take_snapshots {
 
 	my @newsnaps;
 
+	# get utc timestamp of the current day for DST check
+	my $daystartUtc = timelocal(0, 0, 0, $datestamp{'mday'}, ($datestamp{'mon'}-1), $datestamp{'year'});
+	my ($isdst) = (localtime($daystartUtc))[8];
+	my $dstOffset = 0;
+
+	if ($isdst ne $datestamp{'isdst'}) {
+		# current dst is different then at the beginning og the day
+		if ($isdst) {
+			# DST ended in the current day
+			$dstOffset = 60*60;
+		}
+	}
+
 	if ($args{'verbose'}) { print "INFO: taking snapshots...\n"; }
 	foreach my $section (keys %config) {
 		if ($section =~ /^template/) { next; }
@@ -380,6 +393,9 @@ sub take_snapshots {
 				my @preferredtime;
 				my $lastpreferred;
 
+				# to avoid duplicates with DST
+				my $dateSuffix = "";
+
 				if ($type eq 'frequently')     {
 					my $frequentslice = int($datestamp{'min'} / $config{$section}{'frequent_period'});
 
@@ -399,6 +415,13 @@ sub take_snapshots {
 					push @preferredtime,($datestamp{'mon'}-1); # january is month 0
 					push @preferredtime,$datestamp{'year'};
 					$lastpreferred = timelocal(@preferredtime);
+
+					if ($dstOffset ne 0) {
+						# timelocal doesn't take DST into account
+						$lastpreferred += $dstOffset;
+						# DST ended, avoid duplicates
+						$dateSuffix = "_y";
+					}
 					if ($lastpreferred > time()) { $lastpreferred -= 60*60; } # preferred time is later this hour - so look at last hour's
 				} elsif ($type eq 'daily')   {
 					push @preferredtime,0; # try to hit 0 seconds
@@ -408,10 +431,29 @@ sub take_snapshots {
 					push @preferredtime,($datestamp{'mon'}-1); # january is month 0
 					push @preferredtime,$datestamp{'year'};
 					$lastpreferred = timelocal(@preferredtime);
-					if ($lastpreferred > time()) {
-						$preferredtime[3] -= 1; # preferred time is later today - so look at yesterday's
-						$lastpreferred = timelocal(@preferredtime);
+
+					# timelocal doesn't take DST into account
+					$lastpreferred += $dstOffset;
+
+					# check if the planned time has different DST flag than the current
+					my ($isdst) = (localtime($lastpreferred))[8];
+					if ($isdst ne $datestamp{'isdst'}) {
+						if (!$isdst) {
+							# correct DST difference
+							$lastpreferred -= 60*60;
+						}
 					}
+
+					if ($lastpreferred > time()) {
+						$lastpreferred -= 60*60*24;
+
+						if ($dstOffset ne 0) {
+							# because we are going back one day
+							# the DST difference has to be accounted
+							# for in reverse now
+							$lastpreferred -= 2*$dstOffset;
+						}
+					} # preferred time is later today - so look at yesterday's
 				} elsif ($type eq 'weekly')   {
 					# calculate offset in seconds for the desired weekday
 					my $offset = 0;
@@ -463,9 +505,9 @@ sub take_snapshots {
 
 					# use zfs (atomic) recursion if specified in config
 					if ($config{$section}{'zfs_recursion'}) {
-						push(@newsnaps, "$path\@autosnap_$datestamp{'sortable'}_$type\@");
+						push(@newsnaps, "$path\@autosnap_$datestamp{'sortable'}${dateSuffix}_$type\@");
 					} else {
-						push(@newsnaps, "$path\@autosnap_$datestamp{'sortable'}_$type");
+						push(@newsnaps, "$path\@autosnap_$datestamp{'sortable'}${dateSuffix}_$type");
 					}
 				}
 			}

tests/2_dst_handling/run.sh

@@ -13,7 +13,7 @@ set -x
 POOL_NAME="sanoid-test-2"
 POOL_TARGET=""  # root
 RESULT="/tmp/sanoid_test_result"
-RESULT_CHECKSUM="0a6336ccdc948c69563cb56994d190aebbc9b21588aef17bb97e51ae074f879a"
+RESULT_CHECKSUM="a916d9cd46f4b80f285d069f3497d02671bbb1bfd12b43ef93531cbdaf89d55c"
 
 # UTC timestamp of start and end
 START="1509141600"
@@ -49,6 +49,6 @@ done
 saveSnapshotList "${POOL_NAME}" "${RESULT}"
 
 # hourly daily monthly
-verifySnapshotList "${RESULT}" 72 3 1 "${RESULT_CHECKSUM}"
+verifySnapshotList "${RESULT}" 73 3 1 "${RESULT_CHECKSUM}"
 
 # one more hour because of DST