diff --git a/stand/kboot/kboot/hostdisk.c b/stand/kboot/kboot/hostdisk.c
index 423151983523..a9117d4c1c9d 100644
--- a/stand/kboot/kboot/hostdisk.c
+++ b/stand/kboot/kboot/hostdisk.c
@@ -1,621 +1,622 @@
 /*-
  * Copyright (C) 2014 Nathan Whitehorn
  * All rights reserved.
  * Copyright 2022 Netflix, Inc
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  * IN NO EVENT SHALL TOOLS GMBH BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
  * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
  * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
  * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
  * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #include <sys/types.h>
 #include <sys/disk.h>
 #include <stdarg.h>
 #include <paths.h>
 #include "host_syscall.h"
 #include "kboot.h"
 #include "bootstrap.h"
 #ifdef LOADER_ZFS_SUPPORT
 #include "libzfs.h"
 #include <sys/zfs_bootenv.h>
 #endif
 
 static int hostdisk_init(void);
 static int hostdisk_strategy(void *devdata, int flag, daddr_t dblk,
     size_t size, char *buf, size_t *rsize);
 static int hostdisk_open(struct open_file *f, ...);
 static int hostdisk_close(struct open_file *f);
 static int hostdisk_ioctl(struct open_file *f, u_long cmd, void *data);
 static int hostdisk_print(int verbose);
 static char *hostdisk_fmtdev(struct devdesc *vdev);
 static bool hostdisk_match(struct devsw *devsw, const char *devspec);
 static int hostdisk_parsedev(struct devdesc **idev, const char *devspec, const char **path);
 
 struct devsw hostdisk = {
 	.dv_name = "/dev",
 	.dv_type = DEVT_HOSTDISK,
 	.dv_init = hostdisk_init,
 	.dv_strategy = hostdisk_strategy,
 	.dv_open = hostdisk_open,
 	.dv_close = hostdisk_close,
 	.dv_ioctl = hostdisk_ioctl,
 	.dv_print = hostdisk_print,
 	.dv_cleanup = nullsys,
 	.dv_fmtdev = hostdisk_fmtdev,
 	.dv_match = hostdisk_match,
 	.dv_parsedev = hostdisk_parsedev,
 };
 
 /*
  * We need to walk through the /sys/block directories looking for
  * block devices that we can use.
  */
 #define SYSBLK "/sys/block"
 
 #define HOSTDISK_MIN_SIZE (16ul << 20)	/* 16MB */
 
 typedef STAILQ_HEAD(, hdinfo) hdinfo_list_t;
 typedef struct hdinfo {
 	STAILQ_ENTRY(hdinfo)	hd_link;	/* link in device list */
 	hdinfo_list_t	hd_children;
 	struct hdinfo	*hd_parent;
 	const char	*hd_dev;
 	uint64_t	hd_size;		/* In bytes */
 	uint64_t	hd_sectors;
 	uint64_t	hd_sectorsize;
 	int		hd_flags;
 #define HDF_HAS_ZPOOL	1			/* We found a zpool here and uuid valid */
 	uint64_t	hd_zfs_uuid;
 } hdinfo_t;
 
 #define dev2hd(d) ((hdinfo_t *)d->d_opendata)
 #define hd_name(hd) ((hd->hd_dev + 5))
 
 static hdinfo_list_t hdinfo = STAILQ_HEAD_INITIALIZER(hdinfo);
 
 typedef bool fef_cb_t(struct host_dirent64 *, void *);
 #define FEF_RECURSIVE 1
 
 static bool
 foreach_file(const char *dir, fef_cb_t cb, void *argp, u_int flags)
 {
 	char dents[2048];
 	int fd, dentsize;
 	struct host_dirent64 *dent;
 
 	fd = host_open(dir, O_RDONLY, 0);
 	if (fd < 0) {
 		printf("Can't open %s\n", dir);/* XXX */
 		return (false);
 	}
 	while (1) {
 		dentsize = host_getdents64(fd, dents, sizeof(dents));
 		if (dentsize <= 0)
 			break;
 		for (dent = (struct host_dirent64 *)dents;
 		     (char *)dent < dents + dentsize;
 		     dent = (struct host_dirent64 *)((void *)dent + dent->d_reclen)) {
 			if (!cb(dent, argp))
 				break;
 		}
 	}
 	host_close(fd);
 	return (true);
 }
 
 static void
 hostdisk_add_part(hdinfo_t *hd, const char *drv, uint64_t secs)
 {
 	hdinfo_t *md;
 	char *dev;
 
 	printf("hd %s adding %s %ju\n", hd->hd_dev, drv, (uintmax_t)secs);
 	if ((md = calloc(1, sizeof(*md))) == NULL)
 		return;
 	if (asprintf(&dev, "/dev/%s", drv) == -1) {
 		printf("hostdisk: no memory\n");
 		free(md);
 		return;
 	}
 	md->hd_dev = dev;
 	md->hd_sectors = secs;
 	md->hd_sectorsize = hd->hd_sectorsize;
 	md->hd_size = md->hd_sectors * md->hd_sectorsize;
 	md->hd_parent = hd;
 	STAILQ_INSERT_TAIL(&hd->hd_children, md, hd_link);
 }
 
 static bool
 hostdisk_one_part(struct host_dirent64 *dent, void *argp)
 {
 	hdinfo_t *hd = argp;
 	char szfn[1024];
 	uint64_t sz;
 
 	/* Need to skip /dev/ at start of hd_name */
 	if (strncmp(dent->d_name, hd_name(hd), strlen(hd_name(hd))) != 0)
 		return (true);
 	/* Find out how big this is -- no size not a disk */
 	snprintf(szfn, sizeof(szfn), "%s/%s/%s/size", SYSBLK,
 	    hd_name(hd), dent->d_name);
 	if (!file2u64(szfn, &sz))
 		return true;
 	hostdisk_add_part(hd, dent->d_name, sz);
 	return true;
 }
 
 static void
 hostdisk_add_parts(hdinfo_t *hd)
 {
 	char fn[1024];
 
 	snprintf(fn, sizeof(fn), "%s/%s", SYSBLK, hd_name(hd));
 	foreach_file(fn, hostdisk_one_part, hd, 0);
 }
 
 static void
 hostdisk_add_drive(const char *drv, uint64_t secs)
 {
 	hdinfo_t *hd = NULL;
 	char *dev = NULL;
 	char fn[1024];
 
 	if ((hd = calloc(1, sizeof(*hd))) == NULL)
 		return;
 	if (asprintf(&dev, "/dev/%s", drv) == -1) {
 		printf("hostdisk: no memory\n");
 		free(hd);
 		return;
 	}
 	hd->hd_dev = dev;
 	hd->hd_sectors = secs;
 	snprintf(fn, sizeof(fn), "%s/%s/queue/hw_sector_size",
 	    SYSBLK, drv);
 	if (!file2u64(fn, &hd->hd_sectorsize))
 		goto err;
 	hd->hd_size = hd->hd_sectors * hd->hd_sectorsize;
 	if (hd->hd_size < HOSTDISK_MIN_SIZE)
 		goto err;
 	hd->hd_flags = 0;
 	STAILQ_INIT(&hd->hd_children);
 	printf("/dev/%s: %ju %ju %ju\n",
 	    drv, hd->hd_size, hd->hd_sectors, hd->hd_sectorsize);
 	STAILQ_INSERT_TAIL(&hdinfo, hd, hd_link);
 	hostdisk_add_parts(hd);
 	return;
 err:
 	free(dev);
 	free(hd);
 	return;
 }
 
 /* Find a disk / partition by its filename */
 
 static hdinfo_t *
 hostdisk_find(const char *fn)
 {
 	hdinfo_t *hd, *md;
 
 	STAILQ_FOREACH(hd, &hdinfo, hd_link) {
 		if (strcmp(hd->hd_dev, fn) == 0)
 			return (hd);
 		STAILQ_FOREACH(md, &hd->hd_children, hd_link) {
 			if (strcmp(md->hd_dev, fn) == 0)
 				return (md);
 		}
 	}
 	return (NULL);
 }
 
 
 static bool
 hostdisk_one_disk(struct host_dirent64 *dent, void *argp __unused)
 {
 	char szfn[1024];
 	uint64_t sz;
 
 	/*
 	 * Skip . and ..
 	 */
 	if (strcmp(dent->d_name, ".") == 0 ||
 	    strcmp(dent->d_name, "..") == 0)
 		return (true);
 
 	/* Find out how big this is -- no size not a disk */
 	snprintf(szfn, sizeof(szfn), "%s/%s/size", SYSBLK,
 	    dent->d_name);
 	if (!file2u64(szfn, &sz))
 		return (true);
 	hostdisk_add_drive(dent->d_name, sz);
 	return (true);
 }
 
 static void
 hostdisk_fake_one_disk(char *override)
 {
 	hdinfo_t *hd = NULL;
 	struct host_kstat sb;
 
 	if (host_stat(override, &sb) != 0)
 		return;
 	if (!HOST_S_ISREG(sb.st_mode))
 		return;
 	if (sb.st_size == 0)
 		return;
 	if ((hd = calloc(1, sizeof(*hd))) == NULL)
 		return;
 	if ((hd->hd_dev = strdup(override)) == NULL)
 		goto err;
 	hd->hd_size = sb.st_size;
 	hd->hd_sectorsize = 512;	/* XXX configurable? */
 	hd->hd_sectors = hd->hd_size / hd->hd_sectorsize;
 	if (hd->hd_size < HOSTDISK_MIN_SIZE)
 		goto err;
 	hd->hd_flags = 0;
 	STAILQ_INIT(&hd->hd_children);
 	printf("%s: %ju %ju %ju\n",
 	    hd->hd_dev, hd->hd_size, hd->hd_sectors, hd->hd_sectorsize);
 	STAILQ_INSERT_TAIL(&hdinfo, hd, hd_link);
 	return;
 err:
 	free(__DECONST(void *, hd->hd_dev));
 	free(hd);
 }
 
 static void
 hostdisk_find_block_devices(void)
 {
 	char *override;
 
 	override=getenv("hostdisk_override");
 	if (override != NULL)
 		hostdisk_fake_one_disk(override);
 	else
 		foreach_file(SYSBLK, hostdisk_one_disk, NULL, 0);
 }
 
 static int
 hostdisk_init(void)
 {
 	hostdisk_find_block_devices();
 
 	return (0);
 }
 
 static int
 hostdisk_strategy(void *devdata, int flag, daddr_t dblk, size_t size,
     char *buf, size_t *rsize)
 {
 	struct devdesc *desc = devdata;
 	daddr_t pos;
 	int n;
-	int64_t off;
 	uint64_t res;
 	uint32_t posl, posh;
 
 	pos = dblk * 512;
 
 	posl = pos & 0xffffffffu;
 	posh = (pos >> 32) & 0xffffffffu;
-	if ((off = host_llseek(desc->d_unit, posh, posl, &res, 0)) < 0) {
-		printf("Seek error on fd %d to %ju (dblk %ju) returns %jd\n",
-		    desc->d_unit, (uintmax_t)pos, (uintmax_t)dblk, (intmax_t)off);
+	if (host_llseek(desc->d_unit, posh, posl, &res, 0) < 0)
 		return (EIO);
-	}
-	n = host_read(desc->d_unit, buf, size);
+	if (flag & F_READ)
+		n = host_read(desc->d_unit, buf, size);
+	else if (flag & F_WRITE)
+		n = host_write(desc->d_unit, buf, size);
+	else
+		return (EINVAL);
 
 	if (n < 0)
 		return (EIO);
 
 	*rsize = n;
 	return (0);
 }
 
 static int
 hostdisk_open(struct open_file *f, ...)
 {
 	struct devdesc *desc;
 	const char *fn;
 	va_list vl;
 
 	va_start(vl, f);
 	desc = va_arg(vl, struct devdesc *);
 	va_end(vl);
 
 	fn = dev2hd(desc)->hd_dev;
-	desc->d_unit = host_open(fn, O_RDONLY, 0);
+	desc->d_unit = host_open(fn, O_RDWR, 0);
 	if (desc->d_unit <= 0) {
 		printf("hostdisk_open: couldn't open %s: %d\n", fn, errno);
 		return (ENOENT);
 	}
 
 	return (0);
 }
 
 static int
 hostdisk_close(struct open_file *f)
 {
 	struct devdesc *desc = f->f_devdata;
 
 	host_close(desc->d_unit);
 	return (0);
 }
 
 static int
 hostdisk_ioctl(struct open_file *f, u_long cmd, void *data)
 {
 	struct devdesc *desc = f->f_devdata;
 	hdinfo_t *hd = dev2hd(desc);
 
 	switch (cmd) {
 	case DIOCGSECTORSIZE:
 		*(u_int *)data = hd->hd_sectorsize;
 		break;
 	case DIOCGMEDIASIZE:
 		*(uint64_t *)data = hd->hd_size;
 		break;
 	default:
 		return (ENOTTY);
 	}
 	return (0);
 }
 
 static int
 hostdisk_print(int verbose)
 {
 	char line[80];
 	hdinfo_t *hd, *md;
 	int ret = 0;
 
 	printf("%s devices:", hostdisk.dv_name);
 	if (pager_output("\n") != 0)
 		return (1);
 
 	STAILQ_FOREACH(hd, &hdinfo, hd_link) {
 		snprintf(line, sizeof(line),
 		    "   %s: %ju X %ju: %ju bytes\n",
 		    hd->hd_dev,
 		    (uintmax_t)hd->hd_sectors,
 		    (uintmax_t)hd->hd_sectorsize,
 		    (uintmax_t)hd->hd_size);
 		if ((ret = pager_output(line)) != 0)
 			break;
 		STAILQ_FOREACH(md, &hd->hd_children, hd_link) {
 			snprintf(line, sizeof(line),
 			    "     %s: %ju X %ju: %ju bytes\n",
 			    md->hd_dev,
 			    (uintmax_t)md->hd_sectors,
 			    (uintmax_t)md->hd_sectorsize,
 			    (uintmax_t)md->hd_size);
 			if ((ret = pager_output(line)) != 0)
 				goto done;
 		}
 	}
 
 done:
 	return (ret);
 }
 
 static char *
 hostdisk_fmtdev(struct devdesc *vdev)
 {
 	static char name[DEV_DEVLEN];
 
 	snprintf(name, sizeof(name), "%s:", dev2hd(vdev)->hd_dev);
 	return (name);
 }
 
 static bool
 hostdisk_match(struct devsw *devsw, const char *devspec)
 {
 	hdinfo_t *hd;
 	const char *colon;
 	char *cp;
 
 	colon = strchr(devspec, ':');
 	if (colon == NULL)
 		return false;
 	cp = strdup(devspec);
 	cp[colon - devspec] = '\0';
 	hd = hostdisk_find(cp);
 	free(cp);
 	return (hd != NULL);
 }
 
 static int
 hostdisk_parsedev(struct devdesc **idev, const char *devspec, const char **path)
 {
 	const char *cp;
 	struct devdesc *dev;
 	hdinfo_t *hd;
 	int len;
 	char *fn;
 
 	/* Must have a : in it */
 	cp = strchr(devspec, ':');
 	if (cp == NULL)
 		return (EINVAL);
 	/* XXX Stat the /dev or defer error handling to open(2) call? */
 	if (path != NULL)
 		*path = cp + 1;
 	len = cp - devspec;
 	fn = strdup(devspec);
 	fn[len] = '\0';
 	hd = hostdisk_find(fn);
 	if (hd == NULL) {
 		printf("Can't find hdinfo for %s\n", fn);
 		free(fn);
 		return (EINVAL);
 	}
 	free(fn);
 	dev = malloc(sizeof(*dev));
 	if (dev == NULL)
 		return (ENOMEM);
 	dev->d_unit = 0;
 	dev->d_dev = &hostdisk;
 	dev->d_opendata = hd;
 	*idev = dev;
 	return (0);
 }
 
 /* XXX refactor */
 static bool
 sanity_check_currdev(void)
 {
 	struct stat st;
 
 	return (stat(PATH_DEFAULTS_LOADER_CONF, &st) == 0 ||
 #ifdef PATH_BOOTABLE_TOKEN
 	    stat(PATH_BOOTABLE_TOKEN, &st) == 0 || /* non-standard layout */
 #endif
 	    stat(PATH_KERNEL, &st) == 0);
 }
 
 static const char *
 hostdisk_try_one(hdinfo_t *hd)
 {
 	char *fn;
 
 	if (asprintf(&fn, "%s:", hd->hd_dev) == -1)
 		return (NULL);
 	set_currdev(fn);
 	printf("Trying %s\n", fn);
 	if (sanity_check_currdev())
 		return (fn);
 	printf("Failed %s\n", fn);
 	free(fn);
 	return (NULL);
 }
 
 const char *
 hostdisk_gen_probe(void)
 {
 	hdinfo_t *hd, *md;
 	const char *rv = NULL;
 
 	STAILQ_FOREACH(hd, &hdinfo, hd_link) {
 		/* try whole disk */
 		if (hd->hd_flags & HDF_HAS_ZPOOL)
 			continue;
 		rv = hostdisk_try_one(hd);
 		if (rv != NULL)
 			return (rv);
 
 		/* try all partitions */
 		STAILQ_FOREACH(md, &hd->hd_children, hd_link) {
 			if (md->hd_flags & HDF_HAS_ZPOOL)
 				continue;
 			rv = hostdisk_try_one(md);
 			if (rv != NULL)
 				return (rv);
 		}
 	}
 	return (NULL);
 }
 
 #ifdef LOADER_ZFS_SUPPORT
 static bool
 hostdisk_zfs_check_one(hdinfo_t *hd)
 {
 	char *fn;
 	bool found = false;
 	uint64_t pool_uuid;
 
 	if (asprintf(&fn, "%s:", hd->hd_dev) == -1)
 		return (false);
 	pool_uuid = 0;
 	zfs_probe_dev(fn, &pool_uuid, false);
 	if (pool_uuid != 0) {
 		found = true;
 		hd->hd_flags |= HDF_HAS_ZPOOL;
 		hd->hd_zfs_uuid = pool_uuid;
 	}
 	free(fn);
 
 	return (found);
 }
 
 void
 hostdisk_zfs_probe(void)
 {
 	hdinfo_t *hd, *md;
 
 	STAILQ_FOREACH(hd, &hdinfo, hd_link) {
 		if (hostdisk_zfs_check_one(hd))
 			continue;
 		STAILQ_FOREACH(md, &hd->hd_children, hd_link) {
 			hostdisk_zfs_check_one(md);
 		}
 	}
 }
 
 /* This likely shoud move to libsa/zfs/zfs.c and be used by at least EFI booting */
 static bool
 probe_zfs_currdev(uint64_t pool_guid)
 {
 	char *devname;
 	struct zfs_devdesc currdev;
 	char buf[VDEV_PAD_SIZE];
 
 	currdev.dd.d_dev = &zfs_dev;
 	currdev.dd.d_unit = 0;
 	currdev.pool_guid = pool_guid;
 	currdev.root_guid = 0;
 	devname = devformat(&currdev.dd);
 	printf("Setting currdev to %s\n", devname);
 	set_currdev(devname);
 	init_zfs_boot_options(devname);
 
 	if (zfs_get_bootonce(&currdev, OS_BOOTONCE, buf, sizeof(buf)) == 0) {
 		printf("zfs bootonce: %s\n", buf);
 		set_currdev(buf);
 		setenv("zfs-bootonce", buf, 1);
 	}
 	(void)zfs_attach_nvstore(&currdev);
 
 	return (sanity_check_currdev());
 }
 
 static bool
 hostdisk_zfs_try_default(hdinfo_t *hd)
 {
 	return (probe_zfs_currdev(hd->hd_zfs_uuid));
 }
 
 bool
 hostdisk_zfs_find_default(void)
 {
 	hdinfo_t *hd, *md;
 
 	STAILQ_FOREACH(hd, &hdinfo, hd_link) {
 		if (hd->hd_flags & HDF_HAS_ZPOOL) {
 			if (hostdisk_zfs_try_default(hd))
 				return (true);
 			continue;
 		}
 		STAILQ_FOREACH(md, &hd->hd_children, hd_link) {
 			if (md->hd_flags & HDF_HAS_ZPOOL) {
 				if (hostdisk_zfs_try_default(md))
 					return (true);
 			}
 		}
 	}
 	return (false);
 }
 #endif