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diff --git a/sys/boot/common/disk.h b/sys/boot/common/disk.h
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+/*-
+ * Copyright (c) 2011 Google, Inc.
+ * All rights reserved.
+ *
+ * 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 AND CONTRIBUTORS ``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 THE AUTHOR OR CONTRIBUTORS 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.
+ *
+ * $FreeBSD$
+ */
+
+/*
+ * Device descriptor for partitioned disks. We assume that all disk addresses
+ * are 512 byte block offsets from the start of the disk. To use, set the
+ * d_slice and d_partition variables as follows:
+ *
+ * Whole disk access:
+ *
+ * 	d_slice = -1
+ * 	d_partition = -1
+ *
+ * Whole MBR slice:
+ *
+ * 	d_slice = MBR slice number (typically 1..4)
+ * 	d_partition = -1
+ *
+ * BSD disklabel partition within an MBR slice:
+ *
+ * 	d_slice = MBR slice number (typically 1..4)
+ * 	d_partition = disklabel partition (typically 0..7)
+ *
+ * GPT partition:
+ *
+ * 	d_slice = GPT partition number (typically 1..N)
+ * 	d_partition = 255
+ *
+ * For both MBR and GPT, to automatically find the 'best' slice or partition,
+ * set d_slice to zero. This uses the partition type to decide which partition
+ * to use according to the following list of preferences:
+ *
+ * 	FreeBSD (active)
+ * 	FreeBSD (inactive)
+ * 	Linux (active)
+ * 	Linux (inactive)
+ * 	DOS/Windows (active)
+ * 	DOS/Windows (inactive)
+ *
+ * Active MBR slices (marked as bootable) are preferred over inactive. GPT
+ * doesn't have the concept of active/inactive partitions. In both MBR and GPT,
+ * if there are multiple slices/partitions of a given type, the first one
+ * is chosen.
+ *
+ * The low-level disk device will typically call slice_open() from its open
+ * method to interpret the disk partition tables according to the rules above.
+ * This will initialize d_offset to the block offset of the start of the
+ * selected partition - this offset should be added to the offset passed to
+ * the device's strategy method.
+ */
+
+#define DISK_SECSIZE	512
+
+struct disk_devdesc
+{
+	struct devsw	*d_dev;
+	int		d_type;
+	int		d_unit;
+	void		*d_opendata;
+	int		d_slice;
+	int		d_partition;
+	int		d_offset;
+};
+
+/*
+ * Parse disk metadata and initialise dev->d_offset.
+ */
+extern int disk_open(struct disk_devdesc * dev);
+
+/*
+ * Print information about slices on a disk.  For the size calculations we
+ * assume a 512 byte sector.
+ */
+extern void disk_print(struct disk_devdesc *dev, char *prefix, int verbose);