etc/systemd/zfs-mount-generator: rewrite in C

A plain rewrite of the shell version, and generates identical
units, save for replacing some empty lines with nothing, having fewer
meaningless spaces in After=s and different spacing in the lock scripts,
for a clean git diff -w

This is a gain of anywhere from 0m0.336s vs 0m0.022s (15.27x)
to 0m0.202s vs 0m0.006s (33.67x), depending on the hardware,
a.k.a. from "absolutely unusable" to "perfectly fine"

This also properly deals with canmount=noauto units across multiple
pools

See PR for detailed timings (of an early version) and diffs

Reviewed-by: Antonio Russo <[email protected]>
Reviewed-by: Richard Laager <[email protected]>
Reviewed-by: InsanePrawn <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Ahelenia Ziemiańska <[email protected]>
Issue #11915
Closes #11917

5 files changed, 1119 insertions, 491 deletions

diff --git a/Makefile.am b/Makefile.am
index efe99142e..ca9b9053c 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -6,7 +6,7 @@ SUBDIRS += rpm
 endif
 
 if CONFIG_USER
-SUBDIRS += etc man scripts lib tests cmd contrib
+SUBDIRS += man scripts lib tests cmd etc contrib
 if BUILD_LINUX
 SUBDIRS += udev
 endif
diff --git a/etc/systemd/system-generators/Makefile.am b/etc/systemd/system-generators/Makefile.am
index fee88dad8..e5920bf39 100644
--- a/etc/systemd/system-generators/Makefile.am
+++ b/etc/systemd/system-generators/Makefile.am
@@ -1,6 +1,14 @@
-include $(top_srcdir)/config/Substfiles.am
+include $(top_srcdir)/config/Rules.am
 
-systemdgenerator_SCRIPTS = \
+systemdgenerator_PROGRAMS = \
 	zfs-mount-generator
 
-SUBSTFILES += $(systemdgenerator_SCRIPTS)
+zfs_mount_generator_SOURCES = \
+	zfs-mount-generator.c
+
+zfs_mount_generator_LDADD = \
+	$(abs_top_builddir)/lib/libzfs/libzfs.la
+
+zfs_mount_generator_LDFLAGS = -pthread
+
+include $(top_srcdir)/config/CppCheck.am
diff --git a/etc/systemd/system-generators/zfs-mount-generator.c b/etc/systemd/system-generators/zfs-mount-generator.c
new file mode 100644
index 000000000..8deeed9df
--- /dev/null
+++ b/etc/systemd/system-generators/zfs-mount-generator.c
@@ -0,0 +1,1089 @@
+/*
+ * Copyright (c) 2017 Antonio Russo <[email protected]>
+ * Copyright (c) 2020 InsanePrawn <[email protected]>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+
+#include <sys/resource.h>
+#include <sys/types.h>
+#include <sys/time.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
+#include <sys/mman.h>
+#include <semaphore.h>
+#include <stdbool.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <time.h>
+#include <regex.h>
+#include <search.h>
+#include <dirent.h>
+#include <string.h>
+#include <stdlib.h>
+#include <limits.h>
+#include <errno.h>
+#include <libzfs.h>
+
+#define	STRCMP ((int(*)(const void *, const void *))&strcmp)
+#define	PID_T_CMP ((int(*)(const void *, const void *))&pid_t_cmp)
+
+static int
+pid_t_cmp(const pid_t *lhs, const pid_t *rhs)
+{
+	/*
+	 * This is always valid, quoth sys_types.h(7posix):
+	 * > blksize_t, pid_t, and ssize_t shall be signed integer types.
+	 */
+	return (*lhs - *rhs);
+}
+
+#define	EXIT_ENOMEM() \
+	do { \
+		fprintf(stderr, PROGNAME "[%d]: " \
+		    "not enough memory (L%d)!\n", getpid(), __LINE__); \
+		_exit(1); \
+	} while (0)
+
+
+#define	PROGNAME "zfs-mount-generator"
+#define	FSLIST SYSCONFDIR "/zfs/zfs-list.cache"
+#define	ZFS SBINDIR "/zfs"
+
+#define	OUTPUT_HEADER \
+	"# Automatically generated by " PROGNAME "\n" \
+	"\n"
+
+/*
+ * Starts like the one in libzfs_util.c but also matches "//"
+ * and captures until the end, since we actually use it for path extraxion
+ */
+#define	URI_REGEX_S "^\\([A-Za-z][A-Za-z0-9+.\\-]*\\):\\/\\/\\(.*\\)$"
+static regex_t uri_regex;
+
+static char *argv0;
+
+static const char *destdir = "/tmp";
+static int destdir_fd = -1;
+
+static void *known_pools = NULL; /* tsearch() of C strings */
+static struct {
+	sem_t noauto_not_on_sem;
+
+	sem_t noauto_names_sem;
+	size_t noauto_names_len;
+	size_t noauto_names_max;
+	char noauto_names[][NAME_MAX];
+} *noauto_files;
+
+
+static char *
+systemd_escape(const char *input, const char *prepend, const char *append)
+{
+	size_t len = strlen(input);
+	size_t applen = strlen(append);
+	size_t prelen = strlen(prepend);
+	char *ret = malloc(4 * len + prelen + applen + 1);
+	if (!ret)
+		EXIT_ENOMEM();
+
+	memcpy(ret, prepend, prelen);
+	char *out = ret + prelen;
+
+	const char *cur = input;
+	if (*cur == '.') {
+		memcpy(out, "\\x2e", 4);
+		out += 4;
+		++cur;
+	}
+	for (; *cur; ++cur) {
+		if (*cur == '/')
+			*(out++) = '-';
+		else if (strchr(
+		    "0123456789"
+		    "abcdefghijklmnopqrstuvwxyz"
+		    "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+		    ":_.", *cur))
+			*(out++) = *cur;
+		else {
+			sprintf(out, "\\x%02x", (int)*cur);
+			out += 4;
+		}
+	}
+
+	memcpy(out, append, applen + 1);
+	return (ret);
+}
+
+static void
+simplify_path(char *path)
+{
+	char *out = path;
+	for (char *cur = path; *cur; ++cur) {
+		if (*cur == '/') {
+			while (*(cur + 1) == '/')
+				++cur;
+			*(out++) = '/';
+		} else
+			*(out++) = *cur;
+	}
+
+	*(out++) = '\0';
+}
+
+static bool
+strendswith(const char *what, const char *suff)
+{
+	size_t what_l = strlen(what);
+	size_t suff_l = strlen(suff);
+
+	return ((what_l >= suff_l) &&
+	    (strcmp(what + what_l - suff_l, suff) == 0));
+}
+
+/* Assumes already-simplified path, doesn't modify input */
+static char *
+systemd_escape_path(char *input, const char *prepend, const char *append)
+{
+	if (strcmp(input, "/") == 0) {
+		char *ret;
+		if (asprintf(&ret, "%s-%s", prepend, append) == -1)
+			EXIT_ENOMEM();
+		return (ret);
+	} else {
+		/*
+		 * path_is_normalized() (flattened for absolute paths here),
+		 * required for proper escaping
+		 */
+		if (strstr(input, "/./") || strstr(input, "/../") ||
+		    strendswith(input, "/.") || strendswith(input, "/.."))
+			return (NULL);
+
+
+		if (input[0] == '/')
+			++input;
+
+		char *back = &input[strlen(input) - 1];
+		bool deslash = *back == '/';
+		if (deslash)
+			*back = '\0';
+
+		char *ret = systemd_escape(input, prepend, append);
+
+		if (deslash)
+			*back = '/';
+		return (ret);
+	}
+}
+
+static FILE *
+fopenat(int dirfd, const char *pathname, int flags,
+    const char *stream_mode, mode_t mode)
+{
+	int fd = openat(dirfd, pathname, flags, mode);
+	if (fd < 0)
+		return (NULL);
+
+	return (fdopen(fd, stream_mode));
+}
+
+static int
+line_worker(char *line, const char *cachefile)
+{
+	char *toktmp;
+	/* BEGIN CSTYLED */
+	const char *dataset                     = strtok_r(line, "\t", &toktmp);
+	      char *p_mountpoint                = strtok_r(NULL, "\t", &toktmp);
+	const char *p_canmount                  = strtok_r(NULL, "\t", &toktmp);
+	const char *p_atime                     = strtok_r(NULL, "\t", &toktmp);
+	const char *p_relatime                  = strtok_r(NULL, "\t", &toktmp);
+	const char *p_devices                   = strtok_r(NULL, "\t", &toktmp);
+	const char *p_exec                      = strtok_r(NULL, "\t", &toktmp);
+	const char *p_readonly                  = strtok_r(NULL, "\t", &toktmp);
+	const char *p_setuid                    = strtok_r(NULL, "\t", &toktmp);
+	const char *p_nbmand                    = strtok_r(NULL, "\t", &toktmp);
+	const char *p_encroot                   = strtok_r(NULL, "\t", &toktmp) ?: "-";
+	      char *p_keyloc                    = strtok_r(NULL, "\t", &toktmp) ?: strdupa("none");
+	const char *p_systemd_requires          = strtok_r(NULL, "\t", &toktmp) ?: "-";
+	const char *p_systemd_requiresmountsfor = strtok_r(NULL, "\t", &toktmp) ?: "-";
+	const char *p_systemd_before            = strtok_r(NULL, "\t", &toktmp) ?: "-";
+	const char *p_systemd_after             = strtok_r(NULL, "\t", &toktmp) ?: "-";
+	      char *p_systemd_wantedby          = strtok_r(NULL, "\t", &toktmp) ?: strdupa("-");
+	      char *p_systemd_requiredby        = strtok_r(NULL, "\t", &toktmp) ?: strdupa("-");
+	const char *p_systemd_nofail            = strtok_r(NULL, "\t", &toktmp) ?: "-";
+	const char *p_systemd_ignore            = strtok_r(NULL, "\t", &toktmp) ?: "-";
+	/* END CSTYLED */
+
+	const char *pool = dataset;
+	if ((toktmp = strchr(pool, '/')) != NULL)
+		pool = strndupa(pool, toktmp - pool);
+
+	if (p_nbmand == NULL) {
+		fprintf(stderr, PROGNAME "[%d]: %s: not enough tokens!\n",
+		    getpid(), dataset);
+		return (1);
+	}
+
+	strncpy(argv0, dataset, strlen(argv0));
+
+	/* Minimal pre-requisites to mount a ZFS dataset */
+	const char *after = "zfs-import.target";
+	const char *wants = "zfs-import.target";
+	const char *bindsto = NULL;
+	char *wantedby = NULL;
+	char *requiredby = NULL;
+	bool noauto = false;
+	bool wantedby_append = true;
+
+	/*
+	 * zfs-import.target is not needed if the pool is already imported.
+	 * This avoids a dependency loop on root-on-ZFS systems:
+	 *   systemd-random-seed.service After (via RequiresMountsFor)
+	 *   var-lib.mount After
+	 *   zfs-import.target After
+	 *   zfs-import-{cache,scan}.service After
+	 *   cryptsetup.service After
+	 *   systemd-random-seed.service
+	 */
+	if (tfind(pool, &known_pools, STRCMP)) {
+		after = "";
+		wants = "";
+	}
+
+	if (strcmp(p_systemd_after, "-") == 0)
+		p_systemd_after = NULL;
+	if (strcmp(p_systemd_before, "-") == 0)
+		p_systemd_before = NULL;
+	if (strcmp(p_systemd_requires, "-") == 0)
+		p_systemd_requires = NULL;
+	if (strcmp(p_systemd_requiresmountsfor, "-") == 0)
+		p_systemd_requiresmountsfor = NULL;
+
+
+	if (strcmp(p_encroot, "-") != 0) {
+		char *keyloadunit =
+		    systemd_escape(p_encroot, "zfs-load-key-", ".service");
+
+		if (strcmp(dataset, p_encroot) == 0) {
+			const char *keymountdep = NULL;
+			bool is_prompt = false;
+
+			regmatch_t uri_matches[3];
+			if (regexec(&uri_regex, p_keyloc,
+			    sizeof (uri_matches) / sizeof (*uri_matches),
+			    uri_matches, 0) == 0) {
+				p_keyloc[uri_matches[2].rm_eo] = '\0';
+				const char *path =
+				    &p_keyloc[uri_matches[2].rm_so];
+
+				/*
+				 * Assumes all URI keylocations need
+				 * the mount for their path;
+				 * http://, for example, wouldn't
+				 * (but it'd need network-online.target et al.)
+				 */
+				keymountdep = path;
+			} else {
+				if (strcmp(p_keyloc, "prompt") != 0)
+					fprintf(stderr, PROGNAME "[%d]: %s: "
+					    "unknown non-URI keylocation=%s\n",
+					    getpid(), dataset, p_keyloc);
+
+				is_prompt = true;
+			}
+
+
+			/* Generate the key-load .service unit */
+			FILE *keyloadunit_f = fopenat(destdir_fd, keyloadunit,
+			    O_WRONLY | O_CREAT | O_TRUNC | O_CLOEXEC, "w",
+			    0644);
+			if (!keyloadunit_f) {
+				fprintf(stderr, PROGNAME "[%d]: %s: "
+				    "couldn't open %s under %s: %s\n",
+				    getpid(), dataset, keyloadunit, destdir,
+				    strerror(errno));
+				return (1);
+			}
+
+			fprintf(keyloadunit_f,
+			    OUTPUT_HEADER
+			    "[Unit]\n"
+			    "Description=Load ZFS key for %s\n"
+			    "SourcePath=" FSLIST "/%s\n"
+			    "Documentation=man:zfs-mount-generator(8)\n"
+			    "DefaultDependencies=no\n"
+			    "Wants=%s\n"
+			    "After=%s\n",
+			    dataset, cachefile, wants, after);
+
+			if (p_systemd_requires)
+				fprintf(keyloadunit_f,
+				    "Requires=%s\n", p_systemd_requires);
+
+			if (p_systemd_requiresmountsfor || keymountdep) {
+				fprintf(keyloadunit_f, "RequiresMountsFor=");
+				if (p_systemd_requiresmountsfor)
+					fprintf(keyloadunit_f,
+					    "%s ", p_systemd_requiresmountsfor);
+				if (keymountdep)
+					fprintf(keyloadunit_f,
+					    "'%s'", keymountdep);
+				fprintf(keyloadunit_f, "\n");
+			}
+
+			/* BEGIN CSTYLED */
+			fprintf(keyloadunit_f,
+			    "\n"
+			    "[Service]\n"
+			    "Type=oneshot\n"
+			    "RemainAfterExit=yes\n"
+			    "# This avoids a dependency loop involving systemd-journald.socket if this\n"
+			    "# dataset is a parent of the root filesystem.\n"
+			    "StandardOutput=null\n"
+			    "StandardError=null\n"
+			    "ExecStart=/bin/sh -c '"
+			        "set -eu;"
+			        "keystatus=\"$$(" ZFS " get -H -o value keystatus \"%s\")\";"
+			        "[ \"$$keystatus\" = \"unavailable\" ] || exit 0;",
+			    dataset);
+			if (is_prompt)
+				fprintf(keyloadunit_f,
+				    "count=0;"
+				    "while [ $$count -lt 3 ]; do "
+				        "systemd-ask-password --id=\"zfs:%s\" \"Enter passphrase for %s:\" |"
+				        "" ZFS " load-key \"%s\" && exit 0;"
+				        "count=$$((count + 1));"
+				    "done;"
+				    "exit 1",
+				    dataset, dataset, dataset);
+			else
+				fprintf(keyloadunit_f,
+				    "" ZFS " load-key \"%s\"",
+				    dataset);
+
+			fprintf(keyloadunit_f,
+				"'\n"
+				"ExecStop=/bin/sh -c '"
+				    "set -eu;"
+				    "keystatus=\"$$(" ZFS " get -H -o value keystatus \"%s\")\";"
+				    "[ \"$$keystatus\" = \"available\" ] || exit 0;"
+				    "" ZFS " unload-key \"%s\""
+				"'\n",
+				dataset, dataset);
+			/* END CSTYLED */
+
+			(void) fclose(keyloadunit_f);
+		}
+
+		/* Update dependencies for the mount file to want this */
+		bindsto = keyloadunit;
+		if (after[0] == '\0')
+			after = keyloadunit;
+		else if (asprintf(&toktmp, "%s %s", after, keyloadunit) != -1)
+			after = toktmp;
+		else
+			EXIT_ENOMEM();
+	}
+
+
+	/* Skip generation of the mount unit if org.openzfs.systemd:ignore=on */
+	if (strcmp(p_systemd_ignore, "-") == 0 ||
+	    strcmp(p_systemd_ignore, "off") == 0) {
+		/* ok */
+	} else if (strcmp(p_systemd_ignore, "on") == 0)
+		return (0);
+	else {
+		fprintf(stderr, PROGNAME "[%d]: %s: "
+		    "invalid org.openzfs.systemd:ignore=%s\n",
+		    getpid(), dataset, p_systemd_ignore);
+		return (1);
+	}
+
+	/* Check for canmount */
+	if (strcmp(p_canmount, "on") == 0) {
+		/* ok */
+	} else if (strcmp(p_canmount, "noauto") == 0)
+		noauto = true;
+	else if (strcmp(p_canmount, "off") == 0)
+		return (0);
+	else {
+		fprintf(stderr, PROGNAME "[%d]: %s: invalid canmount=%s\n",
+		    getpid(), dataset, p_canmount);
+		return (1);
+	}
+
+	/* Check for legacy and blank mountpoints */
+	if (strcmp(p_mountpoint, "legacy") == 0 ||
+	    strcmp(p_mountpoint, "none") == 0)
+		return (0);
+	else if (p_mountpoint[0] != '/') {
+		fprintf(stderr, PROGNAME "[%d]: %s: invalid mountpoint=%s\n",
+		    getpid(), dataset, p_mountpoint);
+		return (1);
+	}
+
+	/* Escape the mountpoint per systemd policy */
+	simplify_path(p_mountpoint);
+	const char *mountfile = systemd_escape_path(p_mountpoint, "", ".mount");
+	if (mountfile == NULL) {
+		fprintf(stderr,
+		    PROGNAME "[%d]: %s: abnormal simplified mountpoint: %s\n",
+		    getpid(), dataset, p_mountpoint);
+		return (1);
+	}
+
+
+	/*
+	 * Parse options, cf. lib/libzfs/libzfs_mount.c:zfs_add_options
+	 *
+	 * The longest string achievable here is
+	 * ",atime,strictatime,nodev,noexec,rw,nosuid,nomand".
+	 */
+	char opts[64] = "";
+
+	/* atime */
+	if (strcmp(p_atime, "on") == 0) {
+		/* relatime */
+		if (strcmp(p_relatime, "on") == 0)
+			strcat(opts, ",atime,relatime");
+		else if (strcmp(p_relatime, "off") == 0)
+			strcat(opts, ",atime,strictatime");
+		else
+			fprintf(stderr,
+			    PROGNAME "[%d]: %s: invalid relatime=%s\n",
+			    getpid(), dataset, p_relatime);
+	} else if (strcmp(p_atime, "off") == 0) {
+		strcat(opts, ",noatime");
+	} else
+		fprintf(stderr, PROGNAME "[%d]: %s: invalid atime=%s\n",
+		    getpid(), dataset, p_atime);
+
+	/* devices */
+	if (strcmp(p_devices, "on") == 0)
+		strcat(opts, ",dev");
+	else if (strcmp(p_devices, "off") == 0)
+		strcat(opts, ",nodev");
+	else
+		fprintf(stderr, PROGNAME "[%d]: %s: invalid devices=%s\n",
+		    getpid(), dataset, p_devices);
+
+	/* exec */
+	if (strcmp(p_exec, "on") == 0)
+		strcat(opts, ",exec");
+	else if (strcmp(p_exec, "off") == 0)
+		strcat(opts, ",noexec");
+	else
+		fprintf(stderr, PROGNAME "[%d]: %s: invalid exec=%s\n",
+		    getpid(), dataset, p_exec);
+
+	/* readonly */
+	if (strcmp(p_readonly, "on") == 0)
+		strcat(opts, ",ro");
+	else if (strcmp(p_readonly, "off") == 0)
+		strcat(opts, ",rw");
+	else
+		fprintf(stderr, PROGNAME "[%d]: %s: invalid readonly=%s\n",
+		    getpid(), dataset, p_readonly);
+
+	/* setuid */
+	if (strcmp(p_setuid, "on") == 0)
+		strcat(opts, ",suid");
+	else if (strcmp(p_setuid, "off") == 0)
+		strcat(opts, ",nosuid");
+	else
+		fprintf(stderr, PROGNAME "[%d]: %s: invalid setuid=%s\n",
+		    getpid(), dataset, p_setuid);
+
+	/* nbmand */
+	if (strcmp(p_nbmand, "on") == 0)
+		strcat(opts, ",mand");
+	else if (strcmp(p_nbmand, "off") == 0)
+		strcat(opts, ",nomand");
+	else
+		fprintf(stderr, PROGNAME "[%d]: %s: invalid nbmand=%s\n",
+		    getpid(), dataset, p_setuid);
+
+	if (strcmp(p_systemd_wantedby, "-") != 0) {
+		noauto = true;
+
+		if (strcmp(p_systemd_wantedby, "none") != 0)
+			wantedby = p_systemd_wantedby;
+	}
+
+	if (strcmp(p_systemd_requiredby, "-") != 0) {
+		noauto = true;
+
+		if (strcmp(p_systemd_requiredby, "none") != 0)
+			requiredby = p_systemd_requiredby;
+	}
+
+	/*
+	 * For datasets with canmount=on, a dependency is created for
+	 * local-fs.target by default. To avoid regressions, this dependency
+	 * is reduced to "wants" rather than "requires" when nofail!=off.
+	 * **THIS MAY CHANGE**
+	 * noauto=on disables this behavior completely.
+	 */
+	if (!noauto) {
+		if (strcmp(p_systemd_nofail, "off") == 0)
+			requiredby = strdupa("local-fs.target");
+		else {
+			wantedby = strdupa("local-fs.target");
+			wantedby_append = strcmp(p_systemd_nofail, "on") != 0;
+		}
+	}
+
+	/*
+	 * Handle existing files:
+	 * 1.	We never overwrite existing files, although we may delete
+	 * 	files if we're sure they were created by us. (see 5.)
+	 * 2.	We handle files differently based on canmount.
+	 * 	Units with canmount=on always have precedence over noauto.
+	 * 	This is enforced by the noauto_not_on_sem semaphore,
+	 * 	which is only unlocked when the last canmount=on process exits.
+	 * 	It is important to use p_canmount and not noauto here,
+	 * 	since we categorise by canmount while other properties,
+	 * 	e.g. org.openzfs.systemd:wanted-by, also modify noauto.
+	 * 3.	If no unit file exists for a noauto dataset, we create one.
+	 * 	Additionally, we use noauto_files to track the unit file names
+	 * 	(which are the systemd-escaped mountpoints) of all (exclusively)
+	 * 	noauto datasets that had a file created.
+	 * 4.	If the file to be created is found in the tracking array,
+	 * 	we do NOT create it.
+	 * 5.	If a file exists for a noauto dataset,
+	 * 	we check whether the file name is in the array.
+	 * 	If it is, we have multiple noauto datasets for the same
+	 * 	mountpoint. In such cases, we remove the file for safety.
+	 * 	We leave the file name in the tracking array to avoid
+	 * 	further noauto datasets creating a file for this path again.
+	 */
+
+	{
+		sem_t *our_sem = (strcmp(p_canmount, "on") == 0) ?
+		    &noauto_files->noauto_names_sem :
+		    &noauto_files->noauto_not_on_sem;
+		while (sem_wait(our_sem) == -1 && errno == EINTR)
+			;
+	}
+
+	struct stat stbuf;
+	bool already_exists = fstatat(destdir_fd, mountfile, &stbuf, 0) == 0;
+
+	bool is_known = false;
+	for (size_t i = 0; i < noauto_files->noauto_names_len; ++i) {
+		if (strncmp(
+		    noauto_files->noauto_names[i], mountfile, NAME_MAX) == 0) {
+			is_known = true;
+			break;
+		}
+	}
+
+	if (already_exists) {
+		if (is_known) {
+			/* If it's in $noauto_files, we must be noauto too */
+
+			/* See 5 */
+			errno = 0;
+			(void) unlinkat(destdir_fd, mountfile, 0);
+
+			/* See 2 */
+			fprintf(stderr, PROGNAME "[%d]: %s: "
+			    "removing duplicate noauto unit %s%s%s\n",
+			    getpid(), dataset, mountfile,
+			    errno ? "" : " failed: ",
+			    errno ? "" : strerror(errno));
+		} else {
+			/* Don't log for canmount=noauto */
+			if (strcmp(p_canmount, "on") == 0)
+				fprintf(stderr, PROGNAME "[%d]: %s: "
+				    "%s already exists. Skipping.\n",
+				    getpid(), dataset, mountfile);
+		}
+
+		/* File exists: skip current dataset */
+		if (strcmp(p_canmount, "on") == 0)
+			sem_post(&noauto_files->noauto_names_sem);
+		return (0);
+	} else {
+		if (is_known) {
+			/* See 4 */
+			if (strcmp(p_canmount, "on") == 0)
+				sem_post(&noauto_files->noauto_names_sem);
+			return (0);
+		} else if (strcmp(p_canmount, "noauto") == 0) {
+			if (noauto_files->noauto_names_len ==
+			    noauto_files->noauto_names_max)
+				fprintf(stderr, PROGNAME "[%d]: %s: "
+				    "noauto dataset limit (%zu) reached! "
+				    "Not tracking %s. Please report this to "
+				    "https://github.com/openzfs/zfs\n",
+				    getpid(), dataset,
+				    noauto_files->noauto_names_max, mountfile);
+			else {
+				strncpy(noauto_files->noauto_names[
+				    noauto_files->noauto_names_len],
+				    mountfile, NAME_MAX);
+				++noauto_files->noauto_names_len;
+			}
+		}
+	}
+
+
+	FILE *mountfile_f = fopenat(destdir_fd, mountfile,
+	    O_WRONLY | O_CREAT | O_TRUNC | O_CLOEXEC, "w", 0644);
+	if (strcmp(p_canmount, "on") == 0)
+		sem_post(&noauto_files->noauto_names_sem);
+	if (!mountfile_f) {
+		fprintf(stderr,
+		    PROGNAME "[%d]: %s: couldn't open %s under %s: %s\n",
+		    getpid(), dataset, mountfile, destdir, strerror(errno));
+		return (1);
+	}
+
+	fprintf(mountfile_f,
+	    OUTPUT_HEADER
+	    "[Unit]\n"
+	    "SourcePath=" FSLIST "/%s\n"
+	    "Documentation=man:zfs-mount-generator(8)\n"
+	    "\n"
+	    "Before=",
+	    cachefile);
+
+	if (p_systemd_before)
+		fprintf(mountfile_f, "%s ", p_systemd_before);
+	fprintf(mountfile_f, "zfs-mount.service"); /* Ensures we don't race */
+	if (requiredby)
+		fprintf(mountfile_f, " %s", requiredby);
+	if (wantedby && wantedby_append)
+		fprintf(mountfile_f, " %s", wantedby);
+
+	fprintf(mountfile_f,
+	    "\n"
+	    "After=");
+	if (p_systemd_after)
+		fprintf(mountfile_f, "%s ", p_systemd_after);
+	fprintf(mountfile_f, "%s\n", after);
+
+	fprintf(mountfile_f, "Wants=%s\n", wants);
+
+	if (bindsto)
+		fprintf(mountfile_f, "BindsTo=%s\n", bindsto);
+	if (p_systemd_requires)
+		fprintf(mountfile_f, "Requires=%s\n", p_systemd_requires);
+	if (p_systemd_requiresmountsfor)
+		fprintf(mountfile_f,
+		    "RequiresMountsFor=%s\n", p_systemd_requiresmountsfor);
+
+	fprintf(mountfile_f,
+	    "\n"
+	    "[Mount]\n"
+	    "Where=%s\n"
+	    "What=%s\n"
+	    "Type=zfs\n"
+	    "Options=defaults%s,zfsutil\n",
+	    p_mountpoint, dataset, opts);
+
+	(void) fclose(mountfile_f);
+
+	if (!requiredby && !wantedby)
+		return (0);
+
+	/* Finally, create the appropriate dependencies */
+	char *linktgt;
+	if (asprintf(&linktgt, "../%s", mountfile) == -1)
+		EXIT_ENOMEM();
+
+	char *dependencies[][2] = {
+		{"wants", wantedby},
+		{"requires", requiredby},
+		{}
+	};
+	for (__typeof__(&*dependencies) dep = &*dependencies; **dep; ++dep) {
+		if (!(*dep)[1])
+			continue;
+
+		for (char *reqby = strtok_r((*dep)[1], " ", &toktmp);
+		    reqby;
+		    reqby = strtok_r(NULL, " ", &toktmp)) {
+			char *depdir;
+			if (asprintf(&depdir, "%s.%s", reqby, (*dep)[0]) == -1)
+				EXIT_ENOMEM();
+
+			(void) mkdirat(destdir_fd, depdir, 0755);
+			int depdir_fd = openat(destdir_fd, depdir,
+			    O_PATH | O_DIRECTORY | O_CLOEXEC);
+			if (depdir_fd < 0) {
+				fprintf(stderr, PROGNAME "[%d]: %s: "
+				    "couldn't open %s under %s: %s\n",
+				    getpid(), dataset, depdir, destdir,
+				    strerror(errno));
+				free(depdir);
+				continue;
+			}
+
+			if (symlinkat(linktgt, depdir_fd, mountfile) == -1)
+				fprintf(stderr, PROGNAME "[%d]: %s: "
+				    "couldn't symlink at "
+				    "%s under %s under %s: %s\n",
+				    getpid(), dataset, mountfile,
+				    depdir, destdir, strerror(errno));
+
+			(void) close(depdir_fd);
+			free(depdir);
+		}
+	}
+
+	return (0);
+}
+
+
+static int
+pool_enumerator(zpool_handle_t *pool, void *data __attribute__((unused)))
+{
+	int ret = 0;
+
+	/*
+	 * Pools are guaranteed-unique by the kernel,
+	 * no risk of leaking dupes here
+	 */
+	char *name = strdup(zpool_get_name(pool));
+	if (!name || !tsearch(name, &known_pools, STRCMP)) {
+		free(name);
+		ret = ENOMEM;
+	}
+
+	zpool_close(pool);
+	return (ret);
+}
+
+int
+main(int argc, char **argv)
+{
+	struct timespec time_init = {};
+	clock_gettime(CLOCK_MONOTONIC_RAW, &time_init);
+
+	{
+		int kmfd = open("/dev/kmsg", O_WRONLY | O_CLOEXEC);
+		if (kmfd >= 0) {
+			(void) dup2(kmfd, STDERR_FILENO);
+			(void) close(kmfd);
+		}
+	}
+
+	uint8_t debug = 0;
+
+	argv0 = argv[0];
+	switch (argc) {
+	case 1:
+		/* Use default */
+		break;
+	case 2:
+	case 4:
+		destdir = argv[1];
+		break;
+	default:
+		fprintf(stderr,
+		    PROGNAME "[%d]: wrong argument count: %d\n",
+		    getpid(), argc - 1);
+		_exit(1);
+	}
+
+	{
+		destdir_fd = open(destdir, O_PATH | O_DIRECTORY | O_CLOEXEC);
+		if (destdir_fd < 0) {
+			fprintf(stderr, PROGNAME "[%d]: "
+			    "can't open destination directory %s: %s\n",
+			    getpid(), destdir, strerror(errno));
+			_exit(1);
+		}
+	}
+
+	DIR *fslist_dir = opendir(FSLIST);
+	if (!fslist_dir) {
+		if (errno != ENOENT)
+			fprintf(stderr,
+			    PROGNAME "[%d]: couldn't open " FSLIST ": %s\n",
+			    getpid(), strerror(errno));
+		_exit(0);
+	}
+
+	{
+		libzfs_handle_t *libzfs = libzfs_init();
+		if (libzfs) {
+			if (zpool_iter(libzfs, pool_enumerator, NULL) != 0)
+				fprintf(stderr, PROGNAME "[%d]: "
+				    "error listing pools, ignoring\n",
+				    getpid());
+			libzfs_fini(libzfs);
+		} else
+			fprintf(stderr, PROGNAME "[%d]: "
+			    "couldn't start libzfs, ignoring\n",
+			    getpid());
+	}
+
+	{
+		int regerr = regcomp(&uri_regex, URI_REGEX_S, 0);
+		if (regerr != 0) {
+			fprintf(stderr,
+			    PROGNAME "[%d]: invalid regex: %d\n",
+			    getpid(), regerr);
+			_exit(1);
+		}
+	}
+
+	{
+		/*
+		 * We could just get a gigabyte here and Not Care,
+		 * but if vm.overcommit_memory=2, then MAP_NORESERVE is ignored
+		 * and we'd try (and likely fail) to rip it out of swap
+		 */
+		noauto_files = mmap(NULL, 4 * 1024 * 1024,
+		    PROT_READ | PROT_WRITE,
+		    MAP_SHARED | MAP_ANONYMOUS | MAP_NORESERVE, -1, 0);
+		if (noauto_files == MAP_FAILED) {
+			fprintf(stderr,
+			    PROGNAME "[%d]: couldn't allocate IPC region: %s\n",
+			    getpid(), strerror(errno));
+			_exit(1);
+		}
+
+		sem_init(&noauto_files->noauto_not_on_sem, true, 0);
+		sem_init(&noauto_files->noauto_names_sem, true, 1);
+		noauto_files->noauto_names_len = 0;
+		/* Works out to 16447ish, *well* enough */
+		noauto_files->noauto_names_max =
+		    (4 * 1024 * 1024 - sizeof (*noauto_files)) / NAME_MAX;
+	}
+
+	char *line = NULL;
+	size_t linelen = 0;
+	struct timespec time_start = {};
+	{
+		const char *dbgenv = getenv("ZFS_DEBUG");
+		if (dbgenv)
+			debug = atoi(dbgenv);
+		else {
+			FILE *cmdline = fopen("/proc/cmdline", "re");
+			if (cmdline != NULL) {
+				if (getline(&line, &linelen, cmdline) >= 0)
+					debug = strstr(line, "debug") ? 2 : 0;
+				(void) fclose(cmdline);
+			}
+		}
+
+		if (debug && !isatty(STDOUT_FILENO))
+			dup2(STDERR_FILENO, STDOUT_FILENO);
+	}
+
+	size_t forked_canmount_on = 0;
+	size_t forked_canmount_not_on = 0;
+	size_t canmount_on_pids_len = 128;
+	pid_t *canmount_on_pids =
+	    malloc(canmount_on_pids_len * sizeof (*canmount_on_pids));
+	if (canmount_on_pids == NULL)
+		canmount_on_pids_len = 0;
+
+	if (debug)
+		clock_gettime(CLOCK_MONOTONIC_RAW, &time_start);
+
+	ssize_t read;
+	pid_t pid;
+	struct dirent *cachent;
+	while ((cachent = readdir(fslist_dir)) != NULL) {
+		if (strcmp(cachent->d_name, ".") == 0 ||
+		    strcmp(cachent->d_name, "..") == 0)
+			continue;
+
+		FILE *cachefile = fopenat(dirfd(fslist_dir), cachent->d_name,
+		    O_RDONLY | O_CLOEXEC, "r", 0);
+		if (!cachefile) {
+			fprintf(stderr, PROGNAME "[%d]: "
+			    "couldn't open %s under " FSLIST ": %s\n",
+			    getpid(), cachent->d_name, strerror(errno));
+			continue;
+		}
+
+		while ((read = getline(&line, &linelen, cachefile)) >= 0) {
+			line[read - 1] = '\0'; /* newline */
+
+			switch (pid = fork()) {
+			case -1:
+				fprintf(stderr,
+				    PROGNAME "[%d]: couldn't fork for %s: %s\n",
+				    getpid(), line, strerror(errno));
+				break;
+			case 0: /* child */
+				_exit(line_worker(line, cachent->d_name));
+			default: { /* parent */
+				char *tmp;
+				char *dset = strtok_r(line, "\t", &tmp);
+				strtok_r(NULL, "\t", &tmp);
+				char *canmount = strtok_r(NULL, "\t", &tmp);
+				bool canmount_on =
+				    canmount && strncmp(canmount, "on", 2) == 0;
+
+				if (debug >= 2)
+					printf(PROGNAME ": forked %d, "
+					    "canmount_on=%d, dataset=%s\n",
+					    (int)pid, canmount_on, dset);
+
+				if (canmount_on &&
+				    forked_canmount_on ==
+				    canmount_on_pids_len) {
+					size_t new_len =
+					    (canmount_on_pids_len ?: 16) * 2;
+					void *new_pidlist =
+					    realloc(canmount_on_pids,
+					    new_len *
+					    sizeof (*canmount_on_pids));
+					if (!new_pidlist) {
+						fprintf(stderr,
+						    PROGNAME "[%d]: "
+						    "out of memory! "
+						    "Mount ordering may be "
+						    "affected.\n", getpid());
+						continue;
+					}
+
+					canmount_on_pids = new_pidlist;
+					canmount_on_pids_len = new_len;
+				}
+
+				if (canmount_on) {
+					canmount_on_pids[forked_canmount_on] =
+					    pid;
+					++forked_canmount_on;
+				} else
+					++forked_canmount_not_on;
+				break;
+			}
+			}
+		}
+
+		(void) fclose(cachefile);
+	}
+	free(line);
+
+	if (forked_canmount_on == 0) {
+		/* No canmount=on processes to finish, so don't deadlock here */
+		for (size_t i = 0; i < forked_canmount_not_on; ++i)
+			sem_post(&noauto_files->noauto_not_on_sem);
+	} else {
+		/* Likely a no-op, since we got these from a narrow fork loop */
+		qsort(canmount_on_pids, forked_canmount_on,
+		    sizeof (*canmount_on_pids), PID_T_CMP);
+	}
+
+	int status, ret = 0;
+	struct rusage usage;
+	size_t forked_canmount_on_max = forked_canmount_on;
+	while ((pid = wait4(-1, &status, 0, &usage)) != -1) {
+		ret |= WEXITSTATUS(status) | WTERMSIG(status);
+
+		if (forked_canmount_on != 0) {
+			if (bsearch(&pid, canmount_on_pids,
+			    forked_canmount_on_max, sizeof (*canmount_on_pids),
+			    PID_T_CMP))
+				--forked_canmount_on;
+
+			if (forked_canmount_on == 0) {
+				/*
+				 * All canmount=on processes have finished,
+				 * let all the lower-priority ones finish now
+				 */
+				for (size_t i = 0;
+				    i < forked_canmount_not_on; ++i)
+					sem_post(
+					    &noauto_files->noauto_not_on_sem);
+			}
+		}
+
+		if (debug >= 2)
+			printf(PROGNAME ": %d done, user=%llu.%06us, "
+			    "system=%llu.%06us, maxrss=%ldB, ex=0x%x\n",
+			    (int)pid,
+			    (unsigned long long) usage.ru_utime.tv_sec,
+			    (unsigned int) usage.ru_utime.tv_usec,
+			    (unsigned long long) usage.ru_stime.tv_sec,
+			    (unsigned int) usage.ru_stime.tv_usec,
+			    usage.ru_maxrss * 1024, status);
+	}
+
+	if (debug) {
+		struct timespec time_end = {};
+		clock_gettime(CLOCK_MONOTONIC_RAW, &time_end);
+
+		getrusage(RUSAGE_SELF, &usage);
+		printf(
+		    "\n"
+		    PROGNAME ": self    : "
+		    "user=%llu.%06us, system=%llu.%06us, maxrss=%ldB\n",
+		    (unsigned long long) usage.ru_utime.tv_sec,
+		    (unsigned int) usage.ru_utime.tv_usec,
+		    (unsigned long long) usage.ru_stime.tv_sec,
+		    (unsigned int) usage.ru_stime.tv_usec,
+		    usage.ru_maxrss * 1024);
+
+		getrusage(RUSAGE_CHILDREN, &usage);
+		printf(PROGNAME ": children: "
+		    "user=%llu.%06us, system=%llu.%06us, maxrss=%ldB\n",
+		    (unsigned long long) usage.ru_utime.tv_sec,
+		    (unsigned int) usage.ru_utime.tv_usec,
+		    (unsigned long long) usage.ru_stime.tv_sec,
+		    (unsigned int) usage.ru_stime.tv_usec,
+		    usage.ru_maxrss * 1024);
+
+		if (time_start.tv_nsec > time_end.tv_nsec) {
+			time_end.tv_nsec =
+			    1000000000 + time_end.tv_nsec - time_start.tv_nsec;
+			time_end.tv_sec -= 1;
+		} else
+			time_end.tv_nsec -= time_start.tv_nsec;
+		time_end.tv_sec -= time_start.tv_sec;
+
+		if (time_init.tv_nsec > time_start.tv_nsec) {
+			time_start.tv_nsec =
+			    1000000000 + time_start.tv_nsec - time_init.tv_nsec;
+			time_start.tv_sec -= 1;
+		} else
+			time_start.tv_nsec -= time_init.tv_nsec;
+		time_start.tv_sec -= time_init.tv_sec;
+
+		time_init.tv_nsec = time_start.tv_nsec + time_end.tv_nsec;
+		time_init.tv_sec =
+		    time_start.tv_sec + time_end.tv_sec +
+		    time_init.tv_nsec / 1000000000;
+		time_init.tv_nsec %= 1000000000;
+
+		printf(PROGNAME ": wall    : "
+		    "total=%llu.%09llus = "
+		    "init=%llu.%09llus + real=%llu.%09llus\n",
+		    (unsigned long long) time_init.tv_sec,
+		    (unsigned long long) time_init.tv_nsec,
+		    (unsigned long long) time_start.tv_sec,
+		    (unsigned long long) time_start.tv_nsec,
+		    (unsigned long long) time_end.tv_sec,
+		    (unsigned long long) time_end.tv_nsec);
+	}
+
+	_exit(ret);
+}
diff --git a/etc/systemd/system-generators/zfs-mount-generator.in b/etc/systemd/system-generators/zfs-mount-generator.in
deleted file mode 100755
index c276fbbce..000000000
--- a/etc/systemd/system-generators/zfs-mount-generator.in
+++ /dev/null
@@ -1,474 +0,0 @@
-#!/bin/sh
-
-# zfs-mount-generator - generates systemd mount units for zfs
-# Copyright (c) 2017 Antonio Russo <[email protected]>
-# Copyright (c) 2020 InsanePrawn <[email protected]>
-#
-# Permission is hereby granted, free of charge, to any person obtaining
-# a copy of this software and associated documentation files (the
-# "Software"), to deal in the Software without restriction, including
-# without limitation the rights to use, copy, modify, merge, publish,
-# distribute, sublicense, and/or sell copies of the Software, and to
-# permit persons to whom the Software is furnished to do so, subject to
-# the following conditions:
-#
-# The above copyright notice and this permission notice shall be
-# included in all copies or substantial portions of the Software.
-#
-# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
-# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
-# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
-# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
-# LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
-# OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
-# WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
-
-set -e
-
-FSLIST="@sysconfdir@/zfs/zfs-list.cache"
-
-[ -d "${FSLIST}" ] || exit 0
-[ "$(echo "${FSLIST}"/*)" = "${FSLIST}/*" ] && exit 0
-
-do_fail() {
-  printf 'zfs-mount-generator: %s\n' "$*" > /dev/kmsg
-  exit 1
-}
-
-# test if $1 is in space-separated list $2
-is_known() {
-  query="$1"
-  IFS=' '
-  for element in $2 ; do
-    if [ "$query" = "$element" ] ; then
-      return 0
-    fi
-  done
-  return 1
-}
-
-# create dependency on unit file $1
-# of type $2, i.e. "wants" or "requires"
-# in the target units from space-separated list $3
-create_dependencies() {
-  unitfile="$1"
-  suffix="$2"
-  IFS=' '
-  for target in $3 ; do
-    target_dir="${dest_norm}/${target}.${suffix}/"
-    mkdir -p "${target_dir}"
-    ln -s "../${unitfile}" "${target_dir}"
-  done
-}
-
-# see systemd.generator
-if [ $# -eq 0 ] ; then
-  dest_norm="/tmp"
-elif [ $# -eq 3 ] ; then
-  dest_norm="${1}"
-else
-  do_fail "zero or three arguments required"
-fi
-
-pools=$(zpool list -H -o name || true)
-
-# All needed information about each ZFS is available from
-# zfs list -H -t filesystem -o <properties>
-# cached in $FSLIST, and each line is processed by the following function:
-# See the list below for the properties and their order
-
-process_line() {
-
-  # zfs list -H -o name,...
-  # fields are tab separated
-  IFS="$(printf '\t')"
-  # shellcheck disable=SC2086
-  set -- $1
-
-  dataset="${1}"
-  pool="${dataset%%/*}"
-  p_mountpoint="${2}"
-  p_canmount="${3}"
-  p_atime="${4}"
-  p_relatime="${5}"
-  p_devices="${6}"
-  p_exec="${7}"
-  p_readonly="${8}"
-  p_setuid="${9}"
-  p_nbmand="${10}"
-  p_encroot="${11}"
-  p_keyloc="${12}"
-  p_systemd_requires="${13}"
-  p_systemd_requiresmountsfor="${14}"
-  p_systemd_before="${15}"
-  p_systemd_after="${16}"
-  p_systemd_wantedby="${17}"
-  p_systemd_requiredby="${18}"
-  p_systemd_nofail="${19}"
-  p_systemd_ignore="${20}"
-
-  # Minimal pre-requisites to mount a ZFS dataset
-  # By ordering before zfs-mount.service, we avoid race conditions.
-  after="zfs-import.target"
-  before="zfs-mount.service"
-  wants="zfs-import.target"
-  requires=""
-  requiredmounts=""
-  bindsto=""
-  wantedby=""
-  requiredby=""
-  noauto="off"
-
-  # If the pool is already imported, zfs-import.target is not needed.  This
-  # avoids a dependency loop on root-on-ZFS systems:
-  # systemd-random-seed.service After (via RequiresMountsFor) var-lib.mount
-  # After zfs-import.target After zfs-import-{cache,scan}.service After
-  # cryptsetup.service After systemd-random-seed.service.
-  #
-  # Pools are newline-separated and may contain spaces in their names.
-  # There is no better portable way to set IFS to just a newline.  Using
-  # $(printf '\n') doesn't work because $(...) strips trailing newlines.
-  IFS="
-"
-  for p in $pools ; do
-    if [ "$p" = "$pool" ] ; then
-      after=""
-      wants=""
-      break
-    fi
-  done
-
-  if [ -n "${p_systemd_after}" ] && \
-      [ "${p_systemd_after}" != "-" ] ; then
-    after="${p_systemd_after} ${after}"
-  fi
-
-  if [ -n "${p_systemd_before}" ] && \
-      [ "${p_systemd_before}" != "-" ] ; then
-    before="${p_systemd_before} ${before}"
-  fi
-
-  if [ -n "${p_systemd_requires}" ] && \
-      [ "${p_systemd_requires}" != "-" ] ; then
-    requires="Requires=${p_systemd_requires}"
-  fi
-
-  if [ -n "${p_systemd_requiresmountsfor}" ] && \
-      [ "${p_systemd_requiresmountsfor}" != "-" ] ; then
-    requiredmounts="RequiresMountsFor=${p_systemd_requiresmountsfor}"
-  fi
-
-  # Handle encryption
-  if [ -n "${p_encroot}" ] &&
-      [ "${p_encroot}" != "-" ] ; then
-    keyloadunit="zfs-load-key-$(systemd-escape "${p_encroot}").service"
-    if [ "${p_encroot}" = "${dataset}" ] ; then
-      keymountdep=""
-      if [ "${p_keyloc%%://*}" = "file" ] ; then
-        if [ -n "${requiredmounts}" ] ; then
-          keymountdep="${requiredmounts} '${p_keyloc#file://}'"
-        else
-          keymountdep="RequiresMountsFor='${p_keyloc#file://}'"
-        fi
-        keyloadscript="@sbindir@/zfs load-key \"${dataset}\""
-      elif [ "${p_keyloc}" = "prompt" ] ; then
-        keyloadscript="\
-count=0;\
-while [ \$\$count -lt 3 ];do\
-  systemd-ask-password --id=\"zfs:${dataset}\"\
-    \"Enter passphrase for ${dataset}:\"|\
-    @sbindir@/zfs load-key \"${dataset}\" && exit 0;\
-  count=\$\$((count + 1));\
-done;\
-exit 1"
-      else
-        printf 'zfs-mount-generator: (%s) invalid keylocation\n' \
-          "${dataset}" >/dev/kmsg
-      fi
-      keyloadcmd="\
-/bin/sh -c '\
-set -eu;\
-keystatus=\"\$\$(@sbindir@/zfs get -H -o value keystatus \"${dataset}\")\";\
-[ \"\$\$keystatus\" = \"unavailable\" ] || exit 0;\
-${keyloadscript}'"
-      keyunloadcmd="\
-/bin/sh -c '\
-set -eu;\
-keystatus=\"\$\$(@sbindir@/zfs get -H -o value keystatus \"${dataset}\")\";\
-[ \"\$\$keystatus\" = \"available\" ] || exit 0;\
-@sbindir@/zfs unload-key \"${dataset}\"'"
-
-
-
-      # Generate the key-load .service unit
-      #
-      # Note: It is tempting to use a `<<EOF` style here-document for this, but
-      #   bash requires a writable /tmp or $TMPDIR for that. This is not always
-      #   available early during boot.
-      #
-      echo \
-"# Automatically generated by zfs-mount-generator
-
-[Unit]
-Description=Load ZFS key for ${dataset}
-SourcePath=${cachefile}
-Documentation=man:zfs-mount-generator(8)
-DefaultDependencies=no
-Wants=${wants}
-After=${after}
-${requires}
-${keymountdep}
-
-[Service]
-Type=oneshot
-RemainAfterExit=yes
-# This avoids a dependency loop involving systemd-journald.socket if this
-# dataset is a parent of the root filesystem.
-StandardOutput=null
-StandardError=null
-ExecStart=${keyloadcmd}
-ExecStop=${keyunloadcmd}"   > "${dest_norm}/${keyloadunit}"
-    fi
-    # Update the dependencies for the mount file to want the
-    # key-loading unit.
-    wants="${wants}"
-    bindsto="BindsTo=${keyloadunit}"
-    after="${after} ${keyloadunit}"
-  fi
-
-  # Prepare the .mount unit
-
-  # skip generation of the mount unit if org.openzfs.systemd:ignore is "on"
-  if [ -n "${p_systemd_ignore}" ] ; then
-    if [ "${p_systemd_ignore}" = "on" ] ; then
-      return
-    elif [ "${p_systemd_ignore}" = "-" ] \
-      || [ "${p_systemd_ignore}" = "off" ] ; then
-      : # This is OK
-    else
-      do_fail "invalid org.openzfs.systemd:ignore for ${dataset}"
-    fi
-  fi
-
-  # Check for canmount=off .
-  if [ "${p_canmount}" = "off" ] ; then
-    return
-  elif [ "${p_canmount}" = "noauto" ] ; then
-    noauto="on"
-  elif [ "${p_canmount}" = "on" ] ; then
-    : # This is OK
-  else
-    do_fail "invalid canmount for ${dataset}"
-  fi
-
-  # Check for legacy and blank mountpoints.
-  if [ "${p_mountpoint}" = "legacy" ] ; then
-    return
-  elif [ "${p_mountpoint}" = "none" ] ; then
-    return
-  elif [ "${p_mountpoint%"${p_mountpoint#?}"}" != "/" ] ; then
-    do_fail "invalid mountpoint for ${dataset}"
-  fi
-
-  # Escape the mountpoint per systemd policy.
-  mountfile="$(systemd-escape --path --suffix=mount "${p_mountpoint}")"
-
-  # Parse options
-  # see lib/libzfs/libzfs_mount.c:zfs_add_options
-  opts=""
-
-  # atime
-  if [ "${p_atime}" = on ] ; then
-    # relatime
-    if [ "${p_relatime}" = on ] ; then
-      opts="${opts},atime,relatime"
-    elif [ "${p_relatime}" = off ] ; then
-      opts="${opts},atime,strictatime"
-    else
-      printf 'zfs-mount-generator: (%s) invalid relatime\n' \
-        "${dataset}" >/dev/kmsg
-    fi
-  elif [ "${p_atime}" = off ] ; then
-    opts="${opts},noatime"
-  else
-    printf 'zfs-mount-generator: (%s) invalid atime\n' \
-      "${dataset}" >/dev/kmsg
-  fi
-
-  # devices
-  if [ "${p_devices}" = on ] ; then
-    opts="${opts},dev"
-  elif [ "${p_devices}" = off ] ; then
-    opts="${opts},nodev"
-  else
-    printf 'zfs-mount-generator: (%s) invalid devices\n' \
-      "${dataset}" >/dev/kmsg
-  fi
-
-  # exec
-  if [ "${p_exec}" = on ] ; then
-    opts="${opts},exec"
-  elif [ "${p_exec}" = off ] ; then
-    opts="${opts},noexec"
-  else
-    printf 'zfs-mount-generator: (%s) invalid exec\n' \
-      "${dataset}" >/dev/kmsg
-  fi
-
-  # readonly
-  if [ "${p_readonly}" = on ] ; then
-    opts="${opts},ro"
-  elif [ "${p_readonly}" = off ] ; then
-    opts="${opts},rw"
-  else
-    printf 'zfs-mount-generator: (%s) invalid readonly\n' \
-      "${dataset}" >/dev/kmsg
-  fi
-
-  # setuid
-  if [ "${p_setuid}" = on ] ; then
-    opts="${opts},suid"
-  elif [ "${p_setuid}" = off ] ; then
-    opts="${opts},nosuid"
-  else
-    printf 'zfs-mount-generator: (%s) invalid setuid\n' \
-      "${dataset}" >/dev/kmsg
-  fi
-
-  # nbmand
-  if [ "${p_nbmand}" = on ]  ; then
-    opts="${opts},mand"
-  elif [ "${p_nbmand}" = off ] ; then
-    opts="${opts},nomand"
-  else
-    printf 'zfs-mount-generator: (%s) invalid nbmand\n' \
-      "${dataset}" >/dev/kmsg
-  fi
-
-  if [ -n "${p_systemd_wantedby}" ] && \
-      [ "${p_systemd_wantedby}" != "-" ] ; then
-    noauto="on"
-    if [ "${p_systemd_wantedby}" = "none" ] ; then
-      wantedby=""
-    else
-      wantedby="${p_systemd_wantedby}"
-      before="${before} ${wantedby}"
-    fi
-  fi
-
-  if [ -n "${p_systemd_requiredby}" ] && \
-      [ "${p_systemd_requiredby}" != "-" ] ; then
-    noauto="on"
-    if [ "${p_systemd_requiredby}" = "none" ] ; then
-      requiredby=""
-    else
-      requiredby="${p_systemd_requiredby}"
-      before="${before} ${requiredby}"
-    fi
-  fi
-
-  # For datasets with canmount=on, a dependency is created for
-  # local-fs.target by default. To avoid regressions, this dependency
-  # is reduced to "wants" rather than "requires" when nofail is not "off".
-  # **THIS MAY CHANGE**
-  # noauto=on disables this behavior completely.
-  if [ "${noauto}" != "on" ] ; then
-    if [ "${p_systemd_nofail}" = "off" ] ; then
-      requiredby="local-fs.target"
-      before="${before} local-fs.target"
-    else
-      wantedby="local-fs.target"
-      if [ "${p_systemd_nofail}" != "on" ] ; then
-        before="${before} local-fs.target"
-      fi
-    fi
-  fi
-
-  # Handle existing files:
-  # 1.  We never overwrite existing files, although we may delete
-  #     files if we're sure they were created by us. (see 5.)
-  # 2.  We handle files differently based on canmount. Units with canmount=on
-  #     always have precedence over noauto. This is enforced by the sort pipe
-  #     in the loop around this function.
-  #     It is important to use $p_canmount and not $noauto here, since we
-  #     sort by canmount while other properties also modify $noauto, e.g.
-  #     org.openzfs.systemd:wanted-by.
-  # 3.  If no unit file exists for a noauto dataset, we create one.
-  #     Additionally, we use $noauto_files to track the unit file names
-  #     (which are the systemd-escaped mountpoints) of all (exclusively)
-  #     noauto datasets that had a file created.
-  # 4.  If the file to be created is found in the tracking variable,
-  #     we do NOT create it.
-  # 5.  If a file exists for a noauto dataset, we check whether the file
-  #     name is in the variable. If it is, we have multiple noauto datasets
-  #     for the same mountpoint. In such cases, we remove the file for safety.
-  #     To avoid further noauto datasets creating a file for this path again,
-  #     we leave the file name in the tracking variable.
-  if [ -e "${dest_norm}/${mountfile}" ] ; then
-    if is_known "$mountfile" "$noauto_files" ; then
-      # if it's in $noauto_files, we must be noauto too. See 2.
-      printf 'zfs-mount-generator: removing duplicate noauto %s\n' \
-        "${mountfile}" >/dev/kmsg
-      # See 5.
-      rm "${dest_norm}/${mountfile}"
-    else
-      # don't log for canmount=noauto
-      if [  "${p_canmount}" = "on" ] ; then
-        printf 'zfs-mount-generator: %s already exists. Skipping.\n' \
-          "${mountfile}" >/dev/kmsg
-      fi
-    fi
-    # file exists; Skip current dataset.
-    return
-  else
-    if is_known "${mountfile}" "${noauto_files}" ; then
-      # See 4.
-      return
-    elif [ "${p_canmount}" = "noauto" ] ; then
-      noauto_files="${mountfile} ${noauto_files}"
-    fi
-  fi
-
-  # Create the .mount unit file.
-  #
-  # (Do not use `<<EOF`-style here-documents for this, see warning above)
-  #
-  echo \
-"# Automatically generated by zfs-mount-generator
-
-[Unit]
-SourcePath=${cachefile}
-Documentation=man:zfs-mount-generator(8)
-
-Before=${before}
-After=${after}
-Wants=${wants}
-${bindsto}
-${requires}
-${requiredmounts}
-
-[Mount]
-Where=${p_mountpoint}
-What=${dataset}
-Type=zfs
-Options=defaults${opts},zfsutil" > "${dest_norm}/${mountfile}"
-
-  # Finally, create the appropriate dependencies
-  create_dependencies "${mountfile}" "wants" "$wantedby"
-  create_dependencies "${mountfile}" "requires" "$requiredby"
-
-}
-
-for cachefile in "${FSLIST}/"* ; do
-  # Disable glob expansion to protect against special characters when parsing.
-  set -f
-  # Sort cachefile's lines by canmount, "on" before "noauto"
-  # and feed each line into process_line
-  sort -t "$(printf '\t')" -k 3 -r "${cachefile}" | \
-  ( # subshell is necessary for `sort|while read` and $noauto_files
-    noauto_files=""
-    while read -r fs ; do
-      process_line "${fs}"
-    done
-  )
-done
diff --git a/man/man8/zfs-mount-generator.8.in b/man/man8/zfs-mount-generator.8.in
index 96fee4291..6484c0f94 100644
--- a/man/man8/zfs-mount-generator.8.in
+++ b/man/man8/zfs-mount-generator.8.in
@@ -22,7 +22,7 @@
 .\" OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 .\" WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 
-.TH ZFS-MOUNT-GENERATOR 8 "Aug 24, 2020" OpenZFS
+.TH ZFS-MOUNT-GENERATOR 8 "Apr 19, 2021" OpenZFS
 
 .SH "NAME"
 zfs\-mount\-generator \- generates systemd mount units for ZFS
@@ -83,19 +83,13 @@ zfs list -H -o name,mountpoint,canmount,atime,relatime,devices,exec,readonly,set
 .RE
 .PP
 for datasets that should be mounted by systemd, should be kept
-separate from the pool, at
-.PP
-.RS 4
-.RI @sysconfdir@/zfs/zfs-list.cache/ POOLNAME
-.
-.RE
+separate from the pool at
+.RI @sysconfdir@/zfs/zfs-list.cache/ POOLNAME .
 .PP
 The cache file, if writeable, will be kept synchronized with the pool
-state by the ZEDLET
-.PP
-.RS 4
-history_event-zfs-list-cacher.sh .
-.RE
+state by the
+.I history_event-zfs-list-cacher.sh
+ZEDLET.
 .PP
 .sp
 .SS PROPERTIES
@@ -189,6 +183,17 @@ See also
 .BR systemd.mount (5)
 
 .PP
+.SH ENVIRONMENT
+The
+.BR $ZFS_DEBUG
+environment variable, which can either be 0 (default),
+1 (print summary accounting information at the end),
+or at least 2 (print accounting information for each subprocess as it finishes).
+
+If not present, /proc/cmdline is additionally checked for
+.BR debug ,
+in which case the debug level is set to 2.
+
 .SH EXAMPLE
 To begin, enable tracking for the pool:
 .PP
@@ -221,7 +226,7 @@ This forces an update to the stale cache file.
 To test the generator output, run
 .PP
 .RS 4
-@systemdgeneratordir@/zfs-mount-generator /tmp/zfs-mount-generator . .
+@systemdgeneratordir@/zfs-mount-generator /tmp/zfs-mount-generator
 .RE
 .PP
 This will generate units and dependencies in