sortix--sortix/init/init.c

/*
 * Copyright (c) 2011, 2012, 2013, 2014, 2015, 2016 Jonas 'Sortie' Termansen.
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 *
 * init.c
 * Start the operating system.
 */

#include <sys/display.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>

#include <assert.h>
#include <ctype.h>
#include <err.h>
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <fstab.h>
#include <grp.h>
#include <locale.h>
#include <pwd.h>
#include <signal.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <termios.h>
#include <time.h>
#include <timespec.h>
#include <unistd.h>

#include <fsmarshall.h>

#include <mount/blockdevice.h>
#include <mount/devices.h>
#include <mount/filesystem.h>
#include <mount/harddisk.h>
#include <mount/partition.h>
#include <mount/uuid.h>

struct device_match
{
	const char* path;
	struct blockdevice* bdev;
};

struct mountpoint
{
	struct fstab entry;
	char* entry_line;
	pid_t pid;
	char* absolute;
};

static pid_t main_pid;

static struct harddisk** hds = NULL;
static size_t hds_used = 0;
static size_t hds_length = 0;

static struct mountpoint* mountpoints = NULL;
static size_t mountpoints_used = 0;
static size_t mountpoints_length = 0;

static bool chain_location_made = false;
static char chain_location[] = "/tmp/fs.XXXXXX";
static bool chain_location_dev_made = false;
static char chain_location_dev[] = "/tmp/fs.XXXXXX/dev";

static char* read_single_line(FILE* fp)
{
	char* ret = NULL;
	size_t ret_size = 0;
	ssize_t ret_length = getline(&ret, &ret_size, fp);
	if ( ret_length < 0 )
	{
		free(ret);
		return NULL;
	}
	if ( ret[ret_length-1] == '\n' )
		ret[--ret_length] = '\0';
	return ret;
}

static char* join_paths(const char* a, const char* b)
{
	size_t a_len = strlen(a);
	bool has_slash = (a_len && a[a_len-1] == '/') || b[0] == '/';
	char* result;
	if ( (has_slash && asprintf(&result, "%s%s", a, b) < 0) ||
	     (!has_slash && asprintf(&result, "%s/%s", a, b) < 0) )
		return NULL;
	return result;
}

__attribute__((noreturn))
__attribute__((format(printf, 1, 2)))
static void fatal(const char* format, ...)
{
	va_list ap;
	va_start(ap, format);
	fprintf(stderr, "%s: fatal: ", program_invocation_name);
	vfprintf(stderr, format, ap);
	fprintf(stderr, "\n");
	fflush(stderr);
	va_end(ap);
	if ( getpid() == main_pid )
		exit(2);
	_exit(2);
}

__attribute__((format(printf, 1, 2)))
static void warning(const char* format, ...)
{
	va_list ap;
	va_start(ap, format);
	fprintf(stderr, "%s: warning: ", program_invocation_name);
	vfprintf(stderr, format, ap);
	fprintf(stderr, "\n");
	fflush(stderr);
	va_end(ap);
}

__attribute__((format(printf, 1, 2)))
static void note(const char* format, ...)
{
	va_list ap;
	va_start(ap, format);
	fprintf(stderr, "%s: ", program_invocation_name);
	vfprintf(stderr, format, ap);
	fprintf(stderr, "\n");
	fflush(stderr);
	va_end(ap);
}

static void prepare_filesystem(const char* path, struct blockdevice* bdev)
{
	enum filesystem_error fserr = blockdevice_inspect_filesystem(&bdev->fs, bdev);
	if ( fserr == FILESYSTEM_ERROR_ABSENT ||
	     fserr == FILESYSTEM_ERROR_UNRECOGNIZED )
		return;
	if ( fserr != FILESYSTEM_ERROR_NONE )
		return warning("probing: %s: %s", path, filesystem_error_string(fserr));
}

static bool prepare_block_device(void* ctx, const char* path)
{
	(void) ctx;
	struct harddisk* hd = harddisk_openat(AT_FDCWD, path, O_RDONLY);
	if ( !hd )
	{
		int true_errno = errno;
		struct stat st;
		if ( lstat(path, &st) == 0 && !S_ISBLK(st.st_mode) )
			return true;
		errno = true_errno;
		fatal("%s: %m", path);
	}
	if ( !harddisk_inspect_blockdevice(hd) )
	{
		if ( errno == ENOTBLK )
			return true;
		if ( errno == EINVAL )
			return warning("%s: %m", path), true;
		fatal("%s: %m", path);
	}
	if ( hds_used == hds_length )
	{
		// TODO: Potential overflow.
		size_t new_length = hds_length ? 2 * hds_length : 16;
		struct harddisk** new_hds = (struct harddisk**)
			reallocarray(hds, new_length, sizeof(struct harddisk*));
		if ( !new_hds )
			fatal("realloc: %m");
		hds = new_hds;
		hds_length = new_length;
	}
	hds[hds_used++] = hd;
	struct blockdevice* bdev = &hd->bdev;
	enum partition_error parterr = blockdevice_get_partition_table(&bdev->pt, bdev);
	if ( parterr == PARTITION_ERROR_ABSENT ||
	     parterr == PARTITION_ERROR_UNRECOGNIZED )
	{
		prepare_filesystem(path, bdev);
		return true;
	}
	else if ( parterr == PARTITION_ERROR_ERRNO )
	{
		if ( errno == EIO || errno == EINVAL )
			warning("%s: %s", path, partition_error_string(parterr));
		else
			fatal("%s: %s", path, partition_error_string(parterr));
		return true;
	}
	else if ( parterr != PARTITION_ERROR_NONE )
	{
		warning("%s: %s", path, partition_error_string(parterr));
		return true;
	}
	for ( size_t i = 0; i < bdev->pt->partitions_count; i++ )
	{
		struct partition* p = bdev->pt->partitions[i];
		assert(p->path);
		struct stat st;
		if ( stat(p->path, &st) == 0 )
		{
			// TODO: Check the existing partition has the right offset and
			//       length, but definitely do not recreate it if it already
			//       exists properly.
		}
		else if ( errno == ENOENT )
		{
			int mountfd = open(p->path, O_RDONLY | O_CREAT | O_EXCL);
			if ( mountfd < 0 )
				fatal("%s:˙%m", p->path);
			int partfd = mkpartition(hd->fd, p->start, p->length);
			if ( partfd < 0 )
				fatal("mkpartition: %s:˙%m", p->path);
			if ( fsm_fsbind(partfd, mountfd, 0) < 0 )
				fatal("fsbind: %s:˙%m", p->path);
			close(partfd);
			close(mountfd);
		}
		else
		{
			fatal("stat: %s: %m", p->path);
		}
		prepare_filesystem(p->path, &p->bdev);
	}
	return true;
}

static void prepare_block_devices(void)
{
	static bool done = false;
	if ( done )
		return;
	done = true;

	if ( !devices_iterate_path(prepare_block_device, NULL) )
		fatal("iterating devices: %m");
}

static void search_by_uuid(const char* uuid_string,
                           void (*cb)(void*, struct device_match*),
                           void* ctx)
{
	unsigned char uuid[16];
	uuid_from_string(uuid, uuid_string);
	for ( size_t i = 0; i < hds_used; i++ )
	{
		struct blockdevice* bdev = &hds[i]->bdev;
		if ( bdev->fs )
		{
			struct filesystem* fs = bdev->fs;
			if ( !(fs->flags & FILESYSTEM_FLAG_UUID) )
				continue;
			if ( memcmp(uuid, fs->uuid, 16) != 0 )
				continue;
			struct device_match match;
			match.path = hds[i]->path;
			match.bdev = bdev;
			cb(ctx, &match);
		}
		else if ( bdev->pt )
		{
			for ( size_t j = 0; j < bdev->pt->partitions_count; j++ )
			{
				struct partition* p = bdev->pt->partitions[j];
				if ( !p->bdev.fs )
					continue;
				struct filesystem* fs = p->bdev.fs;
				if ( !(fs->flags & FILESYSTEM_FLAG_UUID) )
					continue;
				if ( memcmp(uuid, fs->uuid, 16) != 0 )
					continue;
				struct device_match match;
				match.path = p->path;
				match.bdev = &p->bdev;
				cb(ctx, &match);
			}
		}
	}
}

static void ensure_single_device_match(void* ctx, struct device_match* match)
{
	struct device_match* result = (struct device_match*) ctx;
	if ( result->path )
	{
		if ( result->bdev )
			note("duplicate match: %s", result->path);
		result->bdev = NULL;
		note("duplicate match: %s", match->path);
		return;
	}
	*result = *match;
}

static int sort_mountpoint(const void* a_ptr, const void* b_ptr)
{
	const struct mountpoint* a = (const struct mountpoint*) a_ptr;
	const struct mountpoint* b = (const struct mountpoint*) b_ptr;
	return strcmp(a->entry.fs_file, b->entry.fs_file);
}

static void load_fstab(void)
{
	FILE* fp = fopen("/etc/fstab", "r");
	if ( !fp )
	{
		if ( errno == ENOENT )
			return;
		fatal("/etc/fstab: %m");
	}
	char* line = NULL;
	size_t line_size;
	ssize_t line_length;
	while ( 0 < (line_length = getline(&line, &line_size, fp)) )
	{
		if ( line[line_length - 1] == '\n' )
			line[--line_length] = '\0';
		struct fstab fstabent;
		if ( !scanfsent(line, &fstabent) )
			continue;
		if ( mountpoints_used == mountpoints_length )
		{
			size_t new_length = 2 * mountpoints_length;
			if ( !new_length )
				new_length = 16;
			struct mountpoint* new_mountpoints = (struct mountpoint*)
				reallocarray(mountpoints, new_length, sizeof(struct mountpoint));
			if ( !new_mountpoints )
				fatal("malloc: %m");
			mountpoints = new_mountpoints;
			mountpoints_length = new_length;
		}
		struct mountpoint* mountpoint = &mountpoints[mountpoints_used++];
		memcpy(&mountpoint->entry, &fstabent, sizeof(fstabent));
		mountpoint->entry_line = line;
		mountpoint->pid = -1;
		if ( !(mountpoint->absolute = strdup(mountpoint->entry.fs_file)) )
			fatal("malloc: %m");
		line = NULL;
		line_size = 0;
	}
	if ( ferror(fp) )
		fatal("/etc/fstab: %m");
	free(line);
	fclose(fp);
	qsort(mountpoints, mountpoints_used, sizeof(struct mountpoint),
	      sort_mountpoint);
}

static void set_hostname(void)
{
	FILE* fp = fopen("/etc/hostname", "r");
	if ( !fp && errno == ENOENT )
		return;
	if ( !fp )
		return warning("unable to set hostname: /etc/hostname: %m");
	char* hostname = read_single_line(fp);
	fclose(fp);
	if ( !hostname )
		return warning("unable to set hostname: /etc/hostname: %m");
	int ret = sethostname(hostname, strlen(hostname) + 1);
	if ( ret < 0 )
		warning("unable to set hostname: `%s': %m", hostname);
	free(hostname);
}

static void set_kblayout(void)
{
	FILE* fp = fopen("/etc/kblayout", "r");
	if ( !fp && errno == ENOENT )
		return;
	if ( !fp )
		return warning("unable to set keyboard layout: /etc/kblayout: %m");
	char* kblayout = read_single_line(fp);
	fclose(fp);
	if ( !kblayout )
		return warning("unable to set keyboard layout: /etc/kblayout: %m");
	pid_t child_pid = fork();
	if ( child_pid < 0 )
		return warning("unable to set keyboard layout: fork: %m");
	if ( !child_pid )
	{
		execlp("chkblayout", "chkblayout", "--", kblayout, (const char*) NULL);
		warning("setting keyboard layout: chkblayout: %m");
		_exit(127);
	}
	int status;
	waitpid(child_pid, &status, 0);
	free(kblayout);
}

static void set_videomode(void)
{
	FILE* fp = fopen("/etc/videomode", "r");
	if ( !fp && errno == ENOENT )
		return;
	if ( !fp )
		return warning("unable to set video mode: /etc/videomode: %m");
	char* videomode = read_single_line(fp);
	fclose(fp);
	if ( !videomode )
		return warning("unable to set video mode: /etc/videomode: %m");
	unsigned int xres = 0;
	unsigned int yres = 0;
	unsigned int bpp = 0;
	if ( sscanf(videomode, "%ux%ux%u", &xres, &yres, &bpp) != 3 )
	{
		warning("/etc/videomode: Invalid video mode `%s'", videomode);
		free(videomode);
		return;
	}
	free(videomode);
	struct dispmsg_get_crtc_mode get_mode;
	memset(&get_mode, 0, sizeof(get_mode));
	get_mode.msgid = DISPMSG_GET_CRTC_MODE;
	get_mode.device = 0;
	get_mode.connector = 0;
	// Don't set the resolution if it's already correct.
	if ( dispmsg_issue(&get_mode, sizeof(get_mode)) == 0 )
	{
		if ( get_mode.mode.control & DISPMSG_CONTROL_VALID &&
		     !(get_mode.mode.control & DISPMSG_CONTROL_FALLBACK) &&
		     get_mode.mode.fb_format == bpp &&
		     get_mode.mode.view_xres == xres &&
		     get_mode.mode.view_yres == yres )
			return;
	}
	struct dispmsg_set_crtc_mode set_mode;
	memset(&set_mode, 0, sizeof(set_mode));
	set_mode.msgid = DISPMSG_SET_CRTC_MODE;
	set_mode.device = 0;
	set_mode.connector = 0;
	set_mode.mode.driver_index = 0;
	set_mode.mode.magic = 0;
	set_mode.mode.control = DISPMSG_CONTROL_VALID;
	set_mode.mode.fb_format = bpp;
	set_mode.mode.view_xres = xres;
	set_mode.mode.view_yres = yres;
	set_mode.mode.fb_location = 0;
	set_mode.mode.pitch = xres * (bpp / 8);
	set_mode.mode.surf_off_x = 0;
	set_mode.mode.surf_off_y = 0;
	set_mode.mode.start_x = 0;
	set_mode.mode.start_y = 0;
	set_mode.mode.end_x = 0;
	set_mode.mode.end_y = 0;
	set_mode.mode.desktop_height = yres;
	if ( dispmsg_issue(&set_mode, sizeof(set_mode)) < 0 )
		warning("/etc/videomode: Failed to set video mode `%ux%ux%u': %m",
		        xres, yres, bpp);
}

static void init_early(void)
{
	static bool done = false;
	if ( done )
		return;
	done = true;

	// Make sure that we have a /tmp directory.
	umask(0000);
	mkdir("/tmp", 01777);

	// Set the default file creation mask.
	umask(0022);

	// Set up the PATH variable.
	if ( setenv("PATH", "/bin:/sbin", 1) < 0 )
		fatal("setenv: %m");

	// Set the terminal type.
	if ( setenv("TERM", "sortix", 1) < 0 )
		fatal("setenv: %m");
}

static bool is_chain_init_mountpoint(const struct mountpoint* mountpoint)
{
	return !strcmp(mountpoint->entry.fs_file, "/");
}

static struct filesystem* mountpoint_lookup(const struct mountpoint* mountpoint)
{
	const char* path = mountpoint->entry.fs_file;
	const char* spec = mountpoint->entry.fs_spec;
	if ( strncmp(spec, "UUID=", strlen("UUID=")) == 0 )
	{
		const char* uuid = spec + strlen("UUID=");
		if ( !uuid_validate(uuid) )
		{
			warning("%s: `%s' is not a valid uuid", path, uuid);
			return NULL;
		}
		struct device_match match;
		memset(&match, 0, sizeof(match));
		search_by_uuid(uuid, ensure_single_device_match, &match);
		if ( !match.path )
		{
			warning("%s: No devices matching uuid %s were found", path, uuid);
			return NULL;
		}
		if ( !match.bdev )
		{
			warning("%s: Don't know which particular device to boot with uuid "
			        "%s", path, uuid);
			return NULL;
		}
		assert(match.bdev->fs);
		return match.bdev->fs;
	}
	// TODO: Lookup by device name.
	// TODO: Use this function in the chain init case too.
	warning("%s: Don't know how to resolve `%s' to a filesystem", path, spec);
	return NULL;
}

static bool mountpoint_mount(struct mountpoint* mountpoint)
{
	struct filesystem* fs = mountpoint_lookup(mountpoint);
	if ( !fs )
		return false;
	// TODO: It would be ideal to get an exclusive lock so that no other
	//       processes have currently mounted that filesystem.
	struct blockdevice* bdev = fs->bdev;
	const char* bdev_path = bdev->p ? bdev->p->path : bdev->hd->path;
	assert(bdev_path);
	do if ( fs->flags & (FILESYSTEM_FLAG_FSCK_SHOULD | FILESYSTEM_FLAG_FSCK_MUST) )
	{
		assert(fs->fsck);
		if ( fs->flags & FILESYSTEM_FLAG_FSCK_MUST )
			note("%s: Repairing filesystem due to inconsistency...", bdev_path);
		else
			note("%s: Checking filesystem consistency...", bdev_path);
		pid_t child_pid = fork();
		if ( child_pid < 0 )
		{
			if ( fs->flags & FILESYSTEM_FLAG_FSCK_MUST )
			{
				warning("%s: Mandatory repair failed: fork: %m", bdev_path);
				return false;
			}
			warning("%s: Skipping filesystem check: fork: %m:", bdev_path);
			break;
		}
		if ( child_pid == 0 )
		{
			execlp(fs->fsck, fs->fsck, "-fp", "--", bdev_path, (const char*) NULL);
			note("%s: Failed to load filesystem checker: %s: %m", bdev_path, fs->fsck);
			_exit(127);
		}
		int code;
		if ( waitpid(child_pid, &code, 0) < 0 )
			fatal("waitpid: %m");
		if ( WIFEXITED(code) &&
		     (WEXITSTATUS(code) == 0 || WEXITSTATUS(code) == 1) )
		{
			// Successfully checked filesystem.
		}
		else if ( fs->flags & FILESYSTEM_FLAG_FSCK_MUST )
		{
			if ( WIFSIGNALED(code) )
				warning("%s: Mandatory repair failed: %s: %s", bdev_path,
				        fs->fsck, strsignal(WTERMSIG(code)));
			else if ( !WIFEXITED(code) )
				warning("%s: Mandatory repair failed: %s: %s", bdev_path,
				        fs->fsck, "Unexpected unusual termination");
			else if ( WEXITSTATUS(code) == 127 )
				warning("%s: Mandatory repair failed: %s: %s", bdev_path,
				        fs->fsck, "Filesystem checker is absent");
			else if ( WEXITSTATUS(code) & 2 )
				warning("%s: Mandatory repair: %s: %s", bdev_path,
				        fs->fsck, "System reboot is necessary");
			else
				warning("%s: Mandatory repair failed: %s: %s", bdev_path,
				        fs->fsck, "Filesystem checker was unsuccessful");
			return false;
		}
		else
		{
			bool ignore = false;
			if ( WIFSIGNALED(code) )
				warning("%s: Filesystem check failed: %s: %s", bdev_path,
				        fs->fsck, strsignal(WTERMSIG(code)));
			else if ( !WIFEXITED(code) )
				warning("%s: Filesystem check failed: %s: %s", bdev_path,
				        fs->fsck, "Unexpected unusual termination");
			else if ( WEXITSTATUS(code) == 127 )
			{
				warning("%s: Skipping filesystem check: %s: %s", bdev_path,
				        fs->fsck, "Filesystem checker is absent");
				ignore = true;
			}
			else if ( WEXITSTATUS(code) & 2 )
				warning("%s: Filesystem check: %s: %s", bdev_path,
				        fs->fsck, "System reboot is necessary");
			else
				warning("%s: Filesystem check failed: %s: %s", bdev_path,
				        fs->fsck, "Filesystem checker was unsuccessful");
			if ( !ignore )
				return false;
		}
	} while ( 0 );
	if ( !fs->driver )
	{
		warning("%s: Don't know how to mount a %s filesystem",
		        bdev_path, fs->fstype_name);
		return false;
	}
	const char* pretend_where = mountpoint->entry.fs_file;
	const char* where = mountpoint->absolute;
	struct stat st;
	if ( stat(where, &st) < 0 )
	{
		warning("stat: %s: %m", where);
		return false;
	}
	if ( (mountpoint->pid = fork()) < 0 )
	{
		warning("%s: Unable to mount: fork: %m", bdev_path);
		return false;
	}
	// TODO: This design is broken. The filesystem should tell us when it is
	//       ready instead of having to poll like this.
	if ( mountpoint->pid == 0 )
	{
		execlp(fs->driver, fs->driver, "--foreground", bdev_path, where,
		       "--pretend-mount-path", pretend_where, (const char*) NULL);
		warning("%s: Failed to load filesystem driver: %s: %m", bdev_path, fs->driver);
		_exit(127);
	}
	while ( true )
	{
		struct stat newst;
		if ( stat(where, &newst) < 0 )
		{
			warning("stat: %s: %m", where);
			if ( unmount(where, 0) < 0 && errno != ENOMOUNT )
				warning("unmount: %s: %m", where);
			else if ( errno == ENOMOUNT )
				kill(mountpoint->pid, SIGQUIT);
			int code;
			waitpid(mountpoint->pid, &code, 0);
			mountpoint->pid = -1;
			return false;
		}
		if ( newst.st_dev != st.st_dev || newst.st_ino != st.st_ino )
			break;
		int code;
		pid_t child = waitpid(mountpoint->pid, &code, WNOHANG);
		if ( child < 0 )
			fatal("waitpid: %m");
		if ( child != 0 )
		{
			mountpoint->pid = -1;
			if ( WIFSIGNALED(code) )
				warning("%s: Mount failed: %s: %s", bdev_path, fs->driver,
				        strsignal(WTERMSIG(code)));
			else if ( !WIFEXITED(code) )
				warning("%s: Mount failed: %s: %s", bdev_path, fs->driver,
				        "Unexpected unusual termination");
			else if ( WEXITSTATUS(code) == 127 )
				warning("%s: Mount failed: %s: %s", bdev_path, fs->driver,
				        "Filesystem driver is absent");
			else if ( WEXITSTATUS(code) == 0 )
				warning("%s: Mount failed: %s: Unexpected successful exit",
				        bdev_path, fs->driver);
			else
				warning("%s: Mount failed: %s: Exited with status %i", bdev_path,
				        fs->driver, WEXITSTATUS(code));
			return false;
		}
		struct timespec delay = timespec_make(0, 50L * 1000L * 1000L);
		nanosleep(&delay, NULL);
	}
	return true;
}

static void mountpoints_mount(bool is_chain_init)
{
	for ( size_t i = 0; i < mountpoints_used; i++ )
	{
		struct mountpoint* mountpoint = &mountpoints[i];
		if ( is_chain_init_mountpoint(mountpoint) != is_chain_init )
			continue;
		mountpoint_mount(mountpoint);
	}
}

static void mountpoints_unmount(void)
{
	for ( size_t n = mountpoints_used; n != 0; n-- )
	{
		size_t i = n - 1;
		struct mountpoint* mountpoint = &mountpoints[i];
		if ( mountpoint->pid < 0 )
			continue;
		if ( unmount(mountpoint->absolute, 0) < 0 && errno != ENOMOUNT )
			warning("unmount: %s: %m", mountpoint->entry.fs_file);
		else if ( errno == ENOMOUNT )
			kill(mountpoint->pid, SIGQUIT);
		int code;
		if ( waitpid(mountpoint->pid, &code, 0) < 0 )
			note("waitpid: %m");
		mountpoint->pid = -1;
	}
}

// This function must be usable as an atexit handler, which means it is
// undefined behavior for it to invoke exit(), including through calls to fatal
// in any function transitively called by this function.
static void niht(void)
{
	if ( getpid() != main_pid )
		return;

	if ( chain_location_dev_made )
	{
		unmount(chain_location_dev, 0);
		chain_location_dev_made = false;
	}

	mountpoints_unmount();

	if ( chain_location_made )
	{
		rmdir(chain_location);
		chain_location_made = false;
	}
}

static int init(const char* target)
{
	init_early();
	set_hostname();
	set_kblayout();
	set_videomode();
	prepare_block_devices();
	load_fstab();
	mountpoints_mount(false);
	if ( !strcmp(target, "merge") )
	{
		pid_t child_pid = fork();
		if ( child_pid < 0 )
			fatal("fork: %m");
		if ( !child_pid )
		{
			const char* argv[] = { "sysmerge", "--booting", NULL };
			execv("/sysmerge/sbin/sysmerge", (char* const*) argv);
			fatal("Failed to run automatic update: %s: %m", argv[0]);
		}
		int status;
		if ( waitpid(child_pid, &status, 0) < 0 )
			fatal("waitpid");
		if ( WIFEXITED(status) && WEXITSTATUS(status) != 0 )
			fatal("Automatic upgrade failed: Exit status %i",
			      WEXITSTATUS(status));
		else if ( WIFSIGNALED(status) )
			fatal("Automatic upgrade failed: %s", strsignal(WTERMSIG(status)));
		else if ( !WIFEXITED(status) )
			fatal("Automatic upgrade failed: Unexpected unusual termination");
		niht();
		unsetenv("INIT_PID");
		const char* argv[] = { "init", NULL };
		execv("/sbin/init", (char* const*) argv);
		fatal("Failed to load chain init: %s: %m", argv[0]);
	}
	sigset_t oldset, sigttou;
	sigemptyset(&sigttou);
	sigaddset(&sigttou, SIGTTOU);
	int result;
	while ( true )
	{
		struct termios tio;
		if ( tcgetattr(0, &tio) )
			fatal("tcgetattr: %m");
		pid_t child_pid = fork();
		if ( child_pid < 0 )
			fatal("fork: %m");
		if ( !child_pid )
		{
			uid_t uid = getuid();
			pid_t pid = getpid();
			pid_t ppid = getppid();
			if ( setpgid(0, 0) < 0 )
				fatal("setpgid: %m");
			sigprocmask(SIG_BLOCK, &sigttou, &oldset);
			if ( tcsetpgrp(0, pid) < 0 )
				fatal("tcsetpgrp: %m");
			sigprocmask(SIG_SETMASK, &oldset, NULL);
			struct passwd* pwd = getpwuid(uid);
			if ( !pwd )
				fatal("looking up user by uid %" PRIuUID ": %m", uid);
			const char* home = pwd->pw_dir[0] ? pwd->pw_dir : "/";
			const char* shell = pwd->pw_shell[0] ? pwd->pw_shell : "sh";
			char ppid_str[sizeof(pid_t) * 3];
			snprintf(ppid_str, sizeof(ppid_str), "%" PRIiPID, ppid);
			if ( setenv("INIT_PID", ppid_str, 1) < 0 ||
			     setenv("LOGNAME", pwd->pw_name, 1) < 0 ||
			     setenv("USER", pwd->pw_name, 1) < 0 ||
			     setenv("HOME", home, 1) < 0 ||
			     setenv("SHELL", shell, 1) < 0 )
				fatal("setenv: %m");
			if ( chdir(home) < 0 )
				warning("chdir: %s: %m", home);
			const char* program = "login";
			bool activate_terminal = false;
			if ( !strcmp(target, "single-user") )
			{
				activate_terminal = true;
				program = shell;
			}
			if ( !strcmp(target, "sysinstall") )
			{
				activate_terminal = true;
				program = "sysinstall";
			}
			if ( !strcmp(target, "sysupgrade") )
			{
				program = "sysupgrade";
				activate_terminal = true;
			}
			if ( activate_terminal )
			{
				tio.c_cflag |= CREAD;
				if ( tcsetattr(0, TCSANOW, &tio) )
					fatal("tcgetattr: %m");
			}
			const char* argv[] = { program, NULL };
			execvp(program, (char* const*) argv);
			fatal("%s: %m", program);
		}
		int status;
		if ( waitpid(child_pid, &status, 0) < 0 )
			fatal("waitpid");
		sigprocmask(SIG_BLOCK, &sigttou, &oldset);
		if ( tcsetattr(0, TCSAFLUSH, &tio) )
			fatal("tcgetattr: %m");
		if ( tcsetpgrp(0, getpgid(0)) < 0 )
			fatal("tcsetpgrp: %m");
		sigprocmask(SIG_SETMASK, &oldset, NULL);
		const char* back = ": Trying to bring it back up again";
		if ( WIFEXITED(status) )
		{
			result = WEXITSTATUS(status);
			break;
		}
		else if ( WIFSIGNALED(status) )
			note("session: %s%s", strsignal(WTERMSIG(status)), back);
		else
			note("session: Unexpected unusual termination%s", back);
	}
	return result;
}

static int init_chain(const char* target)
{
	init_early();
	prepare_block_devices();
	load_fstab();
	if ( !mkdtemp(chain_location) )
		fatal("mkdtemp: /tmp/fs.XXXXXX: %m");
	chain_location_made = true;
	bool found_root = false;
	for ( size_t i = 0; i < mountpoints_used; i++ )
	{
		struct mountpoint* mountpoint = &mountpoints[i];
		if ( !strcmp(mountpoint->entry.fs_file, "/") )
			found_root = true;
		char* absolute = join_paths(chain_location, mountpoint->absolute);
		free(mountpoint->absolute);
		mountpoint->absolute = absolute;
	}
	if ( !found_root )
		fatal("/etc/fstab: Root filesystem not found in filesystem table");
	mountpoints_mount(true);
	snprintf(chain_location_dev, sizeof(chain_location_dev), "%s/dev",
	         chain_location);
	if ( mkdir(chain_location_dev, 755) < 0 && errno != EEXIST )
		fatal("mkdir: %s: %m", chain_location_dev);
	int old_dev_fd = open("/dev", O_DIRECTORY | O_RDONLY);
	if ( old_dev_fd < 0 )
		fatal("%s: %m", "/dev");
	int new_dev_fd = open(chain_location_dev, O_DIRECTORY | O_RDONLY);
	if ( new_dev_fd < 0 )
		fatal("%s: %m", chain_location_dev);
	if ( fsm_fsbind(old_dev_fd, new_dev_fd, 0) < 0 )
		fatal("mount: `%s' onto `%s': %m", "/dev", chain_location_dev);
	close(new_dev_fd);
	close(old_dev_fd);
	int result;
	while ( true )
	{
		pid_t child_pid = fork();
		if ( child_pid < 0 )
			fatal("fork: %m");
		if ( !child_pid )
		{
			if ( chroot(chain_location) < 0 )
				fatal("chroot: %s: %m", chain_location);
			if ( chdir("/") < 0 )
				fatal("chdir: %s: %m", chain_location);
			unsetenv("INIT_PID");
			if ( !strcmp(target, "chain-merge") )
			{
				const char* argv[] = { "init", "--target=merge", NULL };
				execv("/sysmerge/sbin/init", (char* const*) argv);
				fatal("Failed to load automatic update chain init: %s: %m", argv[0]);
			}
			else
			{
				const char* argv[] = { "init", NULL };
				execv("/sbin/init", (char* const*) argv);
				fatal("Failed to load chain init: %s: %m", argv[0]);
			}
		}
		int status;
		if ( waitpid(child_pid, &status, 0) < 0 )
			fatal("waitpid");
		// Only run an automatic update once.
		if ( !strcmp(target, "chain-merge") )
			target = "chain";
		const char* back = ": Trying to bring it back up again";
		if ( WIFEXITED(status) )
		{
			result = WEXITSTATUS(status);
			break;
		}
		else if ( WIFSIGNALED(status) )
			note("chain init: %s%s", strsignal(WTERMSIG(status)), back);
		else
			note("chain init: Unexpected unusual termination%s", back);
	}
	return result;
}

static void compact_arguments(int* argc, char*** argv)
{
	for ( int i = 0; i < *argc; i++ )
	{
		while ( i < *argc && !(*argv)[i] )
		{
			for ( int n = i; n < *argc; n++ )
				(*argv)[n] = (*argv)[n+1];
			(*argc)--;
		}
	}
}

int main(int argc, char* argv[])
{
	main_pid = getpid();

	setlocale(LC_ALL, "");

	const char* target = NULL;

	for ( int i = 1; i < argc; i++ )
	{
		const char* arg = argv[i];
		if ( arg[0] != '-' || !arg[1] )
			continue;
		argv[i] = NULL;
		if ( !strcmp(arg, "--") )
			break;
		if ( arg[1] != '-' )
		{
			char c;
			while ( (c = *++arg) ) switch ( c )
			{
			default:
				errx(2, "unknown option -- '%c'", c);
			}
		}
		else if ( !strncmp(arg, "--target=", strlen("--target=")) )
			target = arg + strlen("--target=");
		else if ( !strcmp(arg, "--target") )
		{
			if ( i + 1 == argc )
				errx(2, "option '--target' requires an argument");
			target = argv[i+1];
			argv[++i] = NULL;
		}
		else
			errx(2, "unknown option: %s", arg);
	}

	compact_arguments(&argc, &argv);

	char* target_string = NULL;
	if ( !target )
	{
		const char* target_path = "/etc/init/target";
		if ( access(target_path, F_OK) == 0 )
		{
			FILE* target_fp = fopen(target_path, "r");
			if ( !target_fp )
				fatal("%s: %m", target_path);
			target_string = read_single_line(target_fp);
			if ( !target_string )
				fatal("read: %s: %m", target_path);
			target = target_string;
			fclose(target_fp);
		}
		else
			fatal("Refusing to initialize because %s doesn't exist", target_path);
	}

	if ( getenv("INIT_PID") )
		fatal("System is already managed by an init process");

	if ( atexit(niht) != 0 )
		fatal("atexit: %m");

	if ( !strcmp(target, "single-user") ||
	     !strcmp(target, "multi-user") ||
	     !strcmp(target, "sysinstall") ||
	     !strcmp(target, "sysupgrade") ||
	     !strcmp(target, "merge") )
		return init(target);

	if ( !strcmp(target, "chain") ||
	     !strcmp(target, "chain-merge") )
		return init_chain(target);

	fatal("Unknown initialization target `%s'", target);
}