Index: head/sys/boot/common/disk.h
===================================================================
--- head/sys/boot/common/disk.h
+++ head/sys/boot/common/disk.h
@@ -86,7 +86,7 @@
 	void		*d_opendata;
 	int		d_slice;
 	int		d_partition;
-	off_t		d_offset;
+	uint64_t	d_offset;
 };
 
 enum disk_ioctl {
@@ -97,17 +97,17 @@
 /*
  * Parse disk metadata and initialise dev->d_offset.
  */
-extern int disk_open(struct disk_devdesc *dev, off_t mediasize,
+extern int disk_open(struct disk_devdesc *dev, uint64_t mediasize,
     u_int sectorsize, u_int flags);
 #define	DISK_F_NOCACHE	0x0001		/* Do not use metadata caching */
 extern int disk_close(struct disk_devdesc *dev);
 extern void disk_cleanup(const struct devsw *d_dev);
 extern int disk_ioctl(struct disk_devdesc *dev, u_long cmd, void *buf);
-extern int disk_read(struct disk_devdesc *dev, void *buf, off_t offset,
+extern int disk_read(struct disk_devdesc *dev, void *buf, uint64_t offset,
     u_int blocks);
-extern int disk_write(struct disk_devdesc *dev, void *buf, off_t offset,
+extern int disk_write(struct disk_devdesc *dev, void *buf, uint64_t offset,
     u_int blocks);
-extern int ptblread(void *d, void *buf, size_t blocks, off_t offset);
+extern int ptblread(void *d, void *buf, size_t blocks, uint64_t offset);
 
 /*
  * Print information about slices on a disk.
Index: head/sys/boot/common/disk.c
===================================================================
--- head/sys/boot/common/disk.c
+++ head/sys/boot/common/disk.c
@@ -45,7 +45,7 @@
 
 struct open_disk {
 	struct ptable		*table;
-	off_t			mediasize;
+	uint64_t		mediasize;
 	u_int			sectorsize;
 	u_int			flags;
 	int			rcnt;
@@ -64,7 +64,7 @@
 	int			d_partition;
 
 	struct open_disk	*od;
-	off_t			d_offset;
+	uint64_t		d_offset;
 	STAILQ_ENTRY(dentry)	entry;
 #ifdef DISK_DEBUG
 	uint32_t		count;
@@ -171,7 +171,7 @@
 }
 
 int
-ptblread(void *d, void *buf, size_t blocks, off_t offset)
+ptblread(void *d, void *buf, size_t blocks, uint64_t offset)
 {
 	struct disk_devdesc *dev;
 	struct open_disk *od;
@@ -238,7 +238,7 @@
 }
 
 int
-disk_read(struct disk_devdesc *dev, void *buf, off_t offset, u_int blocks)
+disk_read(struct disk_devdesc *dev, void *buf, uint64_t offset, u_int blocks)
 {
 	struct open_disk *od;
 	int ret;
@@ -251,7 +251,7 @@
 }
 
 int
-disk_write(struct disk_devdesc *dev, void *buf, off_t offset, u_int blocks)
+disk_write(struct disk_devdesc *dev, void *buf, uint64_t offset, u_int blocks)
 {
 	struct open_disk *od;
 	int ret;
@@ -274,7 +274,7 @@
 }
 
 int
-disk_open(struct disk_devdesc *dev, off_t mediasize, u_int sectorsize,
+disk_open(struct disk_devdesc *dev, uint64_t mediasize, u_int sectorsize,
     u_int flags)
 {
 	struct open_disk *od;
Index: head/sys/boot/common/part.h
===================================================================
--- head/sys/boot/common/part.h
+++ head/sys/boot/common/part.h
@@ -62,11 +62,11 @@
 };
 
 /* The offset and size are in sectors */
-typedef int (diskread_t)(void *arg, void *buf, size_t blocks, off_t offset);
+typedef int (diskread_t)(void *arg, void *buf, size_t blocks, uint64_t offset);
 typedef int (ptable_iterate_t)(void *arg, const char *partname,
     const struct ptable_entry *part);
 
-struct ptable *ptable_open(void *dev, off_t sectors, uint16_t sectorsize,
+struct ptable *ptable_open(void *dev, uint64_t sectors, uint16_t sectorsize,
     diskread_t *dread);
 void ptable_close(struct ptable *table);
 enum ptable_type ptable_gettype(const struct ptable *table);
Index: head/sys/boot/common/part.c
===================================================================
--- head/sys/boot/common/part.c
+++ head/sys/boot/common/part.c
@@ -584,7 +584,7 @@
 #endif /* LOADER_VTOC8_SUPPORT */
 
 struct ptable*
-ptable_open(void *dev, off_t sectors, uint16_t sectorsize,
+ptable_open(void *dev, uint64_t sectors, uint16_t sectorsize,
     diskread_t *dread)
 {
 	struct dos_partition *dp;
Index: head/sys/boot/i386/libi386/biosdisk.c
===================================================================
--- head/sys/boot/i386/libi386/biosdisk.c
+++ head/sys/boot/i386/libi386/biosdisk.c
@@ -493,7 +493,7 @@
 		*(u_int *)data = BD(dev).bd_sectorsize;
 		break;
 	case DIOCGMEDIASIZE:
-		*(off_t *)data = BD(dev).bd_sectors * BD(dev).bd_sectorsize;
+		*(uint64_t *)data = BD(dev).bd_sectors * BD(dev).bd_sectorsize;
 		break;
 	default:
 		return (ENOTTY);
Index: head/sys/boot/uboot/lib/disk.c
===================================================================
--- head/sys/boot/uboot/lib/disk.c
+++ head/sys/boot/uboot/lib/disk.c
@@ -282,7 +282,7 @@
 		*(u_int *)data = SI(dev).bsize;
 		break;
 	case DIOCGMEDIASIZE:
-		*(off_t *)data = SI(dev).bsize * SI(dev).blocks;
+		*(uint64_t *)data = SI(dev).bsize * SI(dev).blocks;
 		break;
 	default:
 		return (ENOTTY);
Index: head/sys/boot/usb/storage/umass_loader.c
===================================================================
--- head/sys/boot/usb/storage/umass_loader.c
+++ head/sys/boot/usb/storage/umass_loader.c
@@ -143,14 +143,14 @@
 	uint32_t blocksize;
 
 	switch (cmd) {
-	case IOCTL_GET_BLOCK_SIZE:
-	case IOCTL_GET_BLOCKS:
+	case DIOCGSECTORSIZE:
+	case DIOCGMEDIASIZE:
 		if (usb_msc_read_capacity(umass_uaa.device, 0,
 		    &nblock, &blocksize) != 0)
 			return (EINVAL);
 
-		if (cmd == IOCTL_GET_BLOCKS)
-			*(uint32_t*)buf = nblock;
+		if (cmd == DIOCGMEDIASIZE)
+			*(uint64_t*)buf = nblock;
 		else
 			*(uint32_t*)buf = blocksize;
 
Index: head/sys/boot/zfs/zfs.c
===================================================================
--- head/sys/boot/zfs/zfs.c
+++ head/sys/boot/zfs/zfs.c
@@ -417,7 +417,7 @@
 };
 
 static int
-zfs_diskread(void *arg, void *buf, size_t blocks, off_t offset)
+zfs_diskread(void *arg, void *buf, size_t blocks, uint64_t offset)
 {
 	struct zfs_probe_args *ppa;