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早期freebsd实现

The file `bootblock' is an HP boot block set up with the following label:

# /dev//rsd1c:
type: SCSI
disk: 
label: generic boot
flags:
bytes/sector: 512
sectors/track: 32
tracks/cylinder: 16
sectors/cylinder: 512
cylinders: 1160
rpm: 3600
interleave: 1
trackskew: 0
cylinderskew: 0
headswitch: 0           # milliseconds
track-to-track seek: 0  # milliseconds
drivedata: 0 

8 partitions:
#        size   offset    fstype   [fsize bsize   cpg]
  a:    34176      384    4.2BSD     1024  8192    16   # (Cyl.    0*- 67*)
  b:    65536    34560      swap                        # (Cyl.   67*- 195)
  c:   593920        0      boot                        # (Cyl.    0 - 1159)
  d:    34560        0      boot                        # (Cyl.    0 - 67*)
  e:   409600   100096    unused        0     0         # (Cyl.  195*- 995)
  f:    84224   509696    unused        0     0         # (Cyl.  995*- 1159*)

This is sized to fit on the smallest HP disk that is around 300mb (7959B).
	'a' is the same size as vangogh:/nbsd so you can copy over from it.
	'b' is a 32mb swap partition.
	'd' includes bootblock+'a' so you can use it to create the root
	    image (and use it to edit the disklabel if you plan on changing
	    the 'c' partition).
	'e' is 200mb and intended for /usr.
	'f' is what is left over (41mb) and can be used for a very small /var.
	    It can be grown on larger disks to accomodate a larger /var.

To build a boot image you need a spare disk. Assuming your spare disk
is /dev/rsd1 and you have a root image in /dev/rsd0a, you do the following:

1. sleep 10000 < /dev/sd1c		(hold open the disk)
2. disklabel -W /dev/sd1c		(make the label writable)
3. dd if=bootblock of=/dev/rsd1c	(copy out the bootblock)
4. <kill the sleep>			(close the disk)
5. dd if=/dev/rsd0a of=/dev/rsd1a	(copy out the root fs)
6. dd if=/dev/rsd1d of=rootimage	(create a root image file)


The file `bootblock' is created as follows:

1. handcrafting the disklabel and installing with:
	disklabel -R /dev/rsd1c proto

2. creating the boot program via:
	cd /sys/hp300/stand
	make
	make mkboot
	./mkboot dboot tboot tcopy nbsdboot.lif

3. install the boot program with:
	disklabel -B -b nbsdboot.lif /dev/rsd1c

4. copy out the completed boot block:
	dd if=/dev/rsd1c of=bootblock bs=16b count=24