/*
 * Copyright (c) 2017 Antonio Russo <antonio.e.russo@gmail.com>
 * Copyright (c) 2020 InsanePrawn <insane.prawny@gmail.com>
 *
 * 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 -euc '"
			        "[ \"$$(" ZFS " get -H -o value keystatus \"%s\")\" = \"unavailable\" ] || exit 0;",
			    dataset);
			if (is_prompt)
				fprintf(keyloadunit_f,
				    "for i in 1 2 3; do "
				        "systemd-ask-password --id=\"zfs:%s\" \"Enter passphrase for %s:\" |"
				        "" ZFS " load-key \"%s\" && exit 0;"
				    "done;"
				    "exit 1",
				    dataset, dataset, dataset);
			else
				fprintf(keyloadunit_f,
				    "exec " ZFS " load-key \"%s\"",
				    dataset);

			fprintf(keyloadunit_f,
				"'\n"
				"ExecStop=/bin/sh -euc '"
				    "[ \"$$(" ZFS " get -H -o value keystatus \"%s\")\" = \"available\" ] || exit 0;"
				    "exec " 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);
}