Fix truncate(2) mtime and ctime handling

On Linux, ftruncate(2) always changes the file timestamps, even if the
file size is not changed. However, in case of a successfull
truncate(2), the timestamps are updated only if the file size changes.
This translates to the VFS calling the ZFS Posix Layer "setattr"
function (zpl_setattr) with ATTR_MTIME and ATTR_CTIME unconditionally
set on the iattr mask only when doing a ftruncate(2), while the
truncate(2) is left to the filesystem implementation to be dealt with.

This behaviour is consistent with POSIX:2004/SUSv3 specifications
where there's no explicit requirement for file size changes to update
the timestamps only for ftruncate(2):

http://pubs.opengroup.org/onlinepubs/009695399/functions/truncate.html
http://pubs.opengroup.org/onlinepubs/009695399/functions/ftruncate.html

This has been later updated in POSIX:2008/SUSv4 where, for both
truncate(2)/ftruncate(2), there's no mention of this size change
requirement:

http://austingroupbugs.net/view.php?id=489
http://pubs.opengroup.org/onlinepubs/9699919799/functions/truncate.html
http://pubs.opengroup.org/onlinepubs/9699919799/functions/ftruncate.html

Unfortunately the Linux VFS is still calling into the ZPL without
ATTR_MTIME/ATTR_CTIME set in the truncate(2) case: we fix this by
explicitly updating the timestamps when detecting the ATTR_SIZE bit,
which is always set in do_truncate(), on the iattr mask.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: loli10K <ezomori.nozomu@gmail.com>
Closes openzfs#6811
Closes openzfs#6819

module/zfs/zfs_vnops.c

@@ -3155,7 +3155,7 @@ zfs_setattr(struct inode *ip, vattr_t *vap, int flags, cred_t *cr)
 		    &atime, sizeof (atime));
 	}
 
-	if (mask & ATTR_MTIME) {
+	if (mask & (ATTR_MTIME | ATTR_SIZE)) {
 		ZFS_TIME_ENCODE(&vap->va_mtime, mtime);
 		ZTOI(zp)->i_mtime = timespec_trunc(vap->va_mtime,
 		    ZTOI(zp)->i_sb->s_time_gran);
@@ -3164,7 +3164,7 @@ zfs_setattr(struct inode *ip, vattr_t *vap, int flags, cred_t *cr)
 		    mtime, sizeof (mtime));
 	}
 
-	if (mask & ATTR_CTIME) {
+	if (mask & (ATTR_CTIME | ATTR_SIZE)) {
 		ZFS_TIME_ENCODE(&vap->va_ctime, ctime);
 		ZTOI(zp)->i_ctime = timespec_trunc(vap->va_ctime,
 		    ZTOI(zp)->i_sb->s_time_gran);

tests/runfiles/linux.run

@@ -688,7 +688,7 @@ tests = ['tmpfile_001_pos', 'tmpfile_002_pos', 'tmpfile_003_pos']
 tags = ['functional', 'tmpfile']
 
 [tests/functional/truncate]
-tests = ['truncate_001_pos', 'truncate_002_pos']
+tests = ['truncate_001_pos', 'truncate_002_pos', 'truncate_timestamps']
 tags = ['functional', 'truncate']
 
 [tests/functional/upgrade]

tests/zfs-tests/include/math.shlib

@@ -66,3 +66,33 @@ function to_bytes
 
 	return 0
 }
+
+#
+# Verify $a is equal to $b, otherwise raise an error specifying
+# the $type of values being compared
+#
+function verify_eq # <a> <b> <type>
+{
+	typeset a=$1
+	typeset b=$2
+	typeset type=$3
+
+	if [[ $a -ne $b ]]; then
+		log_fail "Compared $type should be equal: $a != $b"
+	fi
+}
+
+#
+# Verify $a is not equal to $b, otherwise raise an error specifying
+# the $type of values being compared
+#
+function verify_ne # <a> <b> <type>
+{
+	typeset a=$1
+	typeset b=$2
+	typeset type=$3
+
+	if [[ $a -eq $b ]]; then
+		log_fail "Compared $type should be not equal: $a == $b"
+	fi
+}

tests/zfs-tests/tests/functional/truncate/.gitignore

@@ -0,0 +1 @@
+/truncate_test

tests/zfs-tests/tests/functional/truncate/Makefile.am

@@ -1,7 +1,16 @@
+include $(top_srcdir)/config/Rules.am
+
 pkgdatadir = $(datadir)/@PACKAGE@/zfs-tests/tests/functional/truncate
+
 dist_pkgdata_SCRIPTS = \
 	setup.ksh \
 	cleanup.ksh \
 	truncate.cfg \
 	truncate_001_pos.ksh \
-	truncate_002_pos.ksh
+	truncate_002_pos.ksh \
+	truncate_timestamps.ksh
+
+pkgexecdir = $(datadir)/@PACKAGE@/zfs-tests/tests/functional/truncate
+
+pkgexec_PROGRAMS = truncate_test
+truncate_test_SOURCES = truncate_test.c

tests/zfs-tests/tests/functional/truncate/truncate_test.c

@@ -0,0 +1,103 @@
+/*
+ * This file and its contents are supplied under the terms of the
+ * Common Development and Distribution License ("CDDL"), version 1.0.
+ * You may only use this file in accordance with the terms of version
+ * 1.0 of the CDDL.
+ *
+ * A full copy of the text of the CDDL should have accompanied this
+ * source.  A copy of the CDDL is also available via the Internet at
+ * http://www.illumos.org/license/CDDL.
+ */
+
+/*
+ * Copyright (c) 2012, 2014 by Delphix. All rights reserved.
+ * Copyright 2017, loli10K <ezomori.nozomu@gmail.com>. All rights reserved.
+ */
+
+#include <fcntl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#define	FSIZE	256*1024*1024
+
+static long	fsize = FSIZE;
+static int	errflag = 0;
+static char	*filename = NULL;
+static int	ftruncflag = 0;
+
+static void parse_options(int argc, char *argv[]);
+
+static void
+usage(char *execname)
+{
+	(void) fprintf(stderr,
+	    "usage: %s [-s filesize] [-f] /path/to/file\n", execname);
+	(void) exit(1);
+}
+
+int
+main(int argc, char *argv[])
+{
+	int fd;
+
+	parse_options(argc, argv);
+
+	if (ftruncflag) {
+		fd = open(filename, O_RDWR|O_CREAT, 0666);
+		if (fd < 0) {
+			perror("open");
+			return (1);
+		}
+		if (ftruncate(fd, fsize) < 0) {
+			perror("ftruncate");
+			return (1);
+		}
+		if (close(fd)) {
+			perror("close");
+			return (1);
+		}
+	} else {
+		if (truncate(filename, fsize) < 0) {
+			perror("truncate");
+			return (1);
+		}
+	}
+	return (0);
+}
+
+static void
+parse_options(int argc, char *argv[])
+{
+	int c;
+	extern char *optarg;
+	extern int optind, optopt;
+
+	while ((c = getopt(argc, argv, "s:f")) != -1) {
+		switch (c) {
+			case 's':
+				fsize = atoi(optarg);
+				break;
+			case 'f':
+				ftruncflag++;
+				break;
+			case ':':
+				(void) fprintf(stderr,
+				    "Option -%c requires an operand\n", optopt);
+				errflag++;
+				break;
+		}
+		if (errflag) {
+			(void) usage(argv[0]);
+		}
+	}
+
+	if (argc <= optind) {
+		(void) fprintf(stderr, "No filename specified\n");
+		usage(argv[0]);
+	}
+	filename = argv[optind];
+}

tests/zfs-tests/tests/functional/truncate/truncate_timestamps.ksh

@@ -0,0 +1,74 @@
+#!/bin/ksh -p
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+
+#
+# Copyright 2017, loli10K <ezomori.nozomu@gmail.com>. All rights reserved.
+#
+
+. $STF_SUITE/tests/functional/truncate/truncate.cfg
+. $STF_SUITE/include/libtest.shlib
+. $STF_SUITE/include/math.shlib
+
+#
+# DESCRIPTION:
+# Ensure both truncate(2)/ftruncate(2) update target file mtime/ctime attributes
+#
+# STRATEGY:
+# 1. Create a file
+# 2. Truncate the file
+# 3. Verify both mtime/ctime are updated
+# 4. Rinse and repeat for both truncate(2) and ftruncate(2) with various sizes
+#
+
+verify_runnable "both"
+
+function verify_truncate # <filename> <filesize> <option>
+{
+	typeset filename="$1"
+	typeset -i size="$2"
+	typeset option="$3"
+
+	log_must mkfile $sizeavg $filename # always start with $sizeavg
+	typeset -i timestm="$(stat -c %Y $filename)"
+	typeset -i timestc="$(stat -c %Z $filename)"
+	log_must sleep 1
+	log_must $STF_SUITE/tests/functional/truncate/truncate_test -s $size $filename $option
+	verify_eq $size "$(stat -c %s $filename)" "size"
+	verify_ne $timestm "$(stat -c %Y $filename)" "mtime"
+	verify_ne $timestc "$(stat -c %Z $filename)" "ctime"
+	log_must rm -f $filename
+}
+
+function cleanup
+{
+	[[ -f $truncfile ]] && rm -f $truncfile
+}
+
+log_assert "Ensure both truncate(2)/ftruncate(2) update target file timestamps"
+log_onexit cleanup
+
+truncfile="$TESTDIR/truncate.$$"
+sizemin="123"
+sizeavg="$((256*1024))"
+sizemax="$((1024*1024))"
+
+# truncate(2)
+verify_truncate $truncfile $sizemin ""
+verify_truncate $truncfile $sizeavg ""
+verify_truncate $truncfile $sizemax ""
+
+# ftruncate(2)
+verify_truncate $truncfile $sizemin "-f"
+verify_truncate $truncfile $sizeavg "-f"
+verify_truncate $truncfile $sizemax "-f"
+
+log_pass "Successful truncation correctly update timestamps"