PREP(8)PREP(8)NAME
prep, fdisk, format, mbr - prepare hard and floppy diskettes, flashes
SYNOPSIS
disk/prep [ -bcfnprw ] [ -a name ]... [ -s sectorsize ] plan9partition
disk/fdisk [ -abfprw ] [ -s sectorsize ] disk
disk/format [ -dfvx ] [ -b bootblock ] [ -c csize ] [ -l label ] [ -r
nresrv ] [ -t type ] disk [ file... ]
disk/mbr [ -9 ] [ -m mbrfile ]
DESCRIPTION
A partition table is stored on a hard disk to specify the division of
the physical disk into a set of logical units. On PCs, the partition
table is stored at the end of the master boot record of the disk. Par‐
titions of type 0x39 are Plan 9 partitions. Inferno uses the same type
and follows other Plan 9 conventions described here. The names of PC
partitions are chosen by convention from the type: dos, plan9, etc.
Second and subsequent partitions of the same type on a given disk are
given unique names by appending a number (or a period and a number if
the name already ends in a number).
Plan 9 partitions (and Plan 9 disks on non-PCs) are themselves divided,
using a textual partition table, called the Plan 9 partition table, in
the second sector of the partition (the first is left for architecture-
specific boot data, such as PC boot blocks). Inferno again uses the
same conventions. The table is a sequence of lines of the format part
name start end, where start and end name the starting and ending sec‐
tor. Sector 0 is the first sector of the Plan 9 partition or disk,
regardless of its position in a larger disk. Partition extents do not
contain the ending sector, so a partition from 0 to 5 and a partition
from 5 to 10 do not overlap.
The Plan 9 partition often contains a number of conventionally named
subpartitions. Only 9fat, fs and nvram are currently used by Inferno,
but the others are included for reference. They include:
9fat A small FAT file system used to hold configuration information
(such as plan9.ini and plan9.nvr) and kernels. This typically
begins in the first sector of the partition, and contains the
partition table as a ``reserved'' sector. See the discussion of
the -r option to format.
arenas A Plan 9 venti arenas partition.
cache A Plan 9 cfs file system cache.
fossil A Plan 9 fossil file system.
fs A kfs(4) file system.
fscfg A one-sector partition used to store a ds(3) configuration.
isect A Plan 9 venti index section.
nvram A one-sector partition used to simulate non-volatile RAM on PCs.
other A non-archived Plan 9 fossil file system.
swap A Plan 9 swap partition.
Fdisk edits the PC partition table and is usually invoked with a disk
like /dev/sdC0/data as its argument, while prep edits the Plan 9 parti‐
tion table and is usually invoked with a disk partition like
/dev/sdC0/plan9 as its argument. Fdisk works in units of disk ``cylin‐
ders'': the cylinder size in bytes is printed when fdisk starts. Prep
works in units of disk sectors, which are almost always 512 bytes.
Fdisk and prep share most of their options:
-a Automatically partition the disk. Fdisk will create a Plan 9
partition in the largest unused area on the disk, doing nothing
if a Plan 9 partition already exists. If no other partition on
the disk is marked active (i.e. marked as the boot partition),
fdisk will mark the new partition active. Prep's -a flag takes
the name of a partition to create. (See the list above for par‐
tition names.) It can be repeated to specify a list of parti‐
tions to create. If the disk is currently unpartitioned, prep
will create the named partitions on the disk, attempting to use
the entire disk in a sensible manner. The partition names must
be from the list given above.
-b Start with a blank disk, ignoring any extant partition table.
-p Print a sequence of commands that when sent to the disk device's
ctl file will bring the partition table information kept by the
sd(3) driver up to date. Then exit. Prep will check to see if
it is being called with a disk partition (rather than an entire
disk) as its argument; if so, it will translate the printed sec‐
tors by the partition's offset within the disk. Since fdisk
operates on a table of unnamed partitions, it assigns names
based on the partition type (e.g., plan9, dos, ntfs, linux, lin‐
uxswap) and resolves collisions by appending a numbered suffix.
(e.g., dos, dos1, dos2).
-r In the absence of the -p and -w flags, prep and fdisk enter an
interactive partition editor; the -r flag runs the editor in
read-only mode.
-s sectorsize
Specify the disk's sector size. In the absence of this flag,
prep and fdisk look for a disk ctl file and read it to find the
disk's sector size. If the ctl file cannot be found, a message
is printed and a sector size of 512 bytes is assumed.
-w Write the partition table to the disk and exit. This is useful
when used in conjunction with -a or -b.
If neither the -p flag nor the -w flag is given, prep and fdisk enter
an interactive partition editor that operates on named partitions. The
PC partition table distinguishes between primary partitions, which can
be listed in the boot sector at the beginning of the disk, and sec‐
ondary (or extended) partitions, arbitrarily many of which may be
chained together in place of a primary partition. Primary partitions
are named pn, secondary partitions sn. The number of primary parti‐
tions plus number of contiguous chains of secondary partitions cannot
exceed four.
The commands are as follows. In the descriptions, read ``sector'' as
``cylinder'' when using fdisk.
a name [ start [ end ] ]
Create a partition named name starting at sector offset start
and ending at offset end. The new partition will not be created
if it overlaps an extant partition. If start or end are omit‐
ted, prep and fdisk will prompt for them. In fdisk, the newly
created partition has type ``PLAN9;'' to set a different type,
use the t command (q.v.). Start and end may be expressions
using the operators +, -, *, and /, numeric constants, and the
pseudovariables . and $. At the start of the program, . is
set to zero; each time a partition is created, it is set to the
end sector of the new partition. It can also be explicitly set
using the . command. When evaluating start, $ is set to one
past the last disk sector. When evaluating end, $ is set to the
maximum value that end can take on without running off the disk
or into another partition. Finally, the expression n% evaluates
to (n×disksize)/100. As an example, a . .+20% creates a new
partition starting at . that takes up a fifth of the disk, and
a 1000 $ creates a new partition starting at sector 1000 and
extending as far as possible.
. newdot
Set the value of the variable . to newdot, which is an arith‐
metic expression as described in the discussion of the a com‐
mand.
d name Delete the named partition.
h Print a help message listing command synopses.
p Print the disk partition table. Unpartitioned regions are also
listed. The table consists of a number of lines containing par‐
tition name, beginning and ending sectors, and total size. A '
is prefixed to the names of partitions whose entries have been
modified but not written to disk. Fdisk adds to the end of each
line a textual partition type, and places a * next to the name
of the active partition (see the A command below).
P Print the partition table in the format accepted by the disk's
ctl file, which is also the format of the output of the -p
option.
w Write the partition table to disk. Prep will also inform the
kernel of the changed partition table. The write will fail if
any programs have any of the disk's partitions open. If the
write fails (for this or any other reason), prep and fdisk will
attempt to restore the partition table to its former state.
q Quit the program. If the partition table has been modified but
not written, a warning is printed. Typing q again will quit the
program.
Fdisk also has the following commands.
A name Set the named partition active. The active partition is the one
whose boot block is used when booting a PC from disk.
e Print the names of empty slots in the partition table, i.e., the
valid names to use when creating a new partition.
t [ type ]
Set the partition type. If it is not given, fdisk will display
a list of choices and then prompt for it.
Format prepares for use the floppy diskette or hard disk partition in
the file named disk, for example /dev/fd0disk or /dev/sdC0/9fat. The
options are:
-f Do not physically format the disc. Used to install a FAT file
system on a previously formatted disc. If disk is not a floppy
device, this flag is a no-op.
-t specify a density and type of disk to be prepared. The possible
types are:
3½DD 3½" double density, 737280 bytes
3½HD 3½" high density, 1474560 bytes
5¼DD 5¼" double density, 368640 bytes
5¼HD 5¼" high density, 1146880 bytes
hard fixed disk
The default when disk is a floppy drive is the highest possible
on the device. When disk is a regular file, the default is
3½HD. When disk is an sd(3) device, the default is hard.
-d initialize a FAT file system on the disk.
-b use the contents of bootblock as a bootstrap block to be
installed in sector 0.
The remaining options have effect only when -d is specified:
-c use a FAT cluster size of csize sectors when creating the FAT.
-l add a label when creating the FAT file system.
-r mark the first nresrv sectors of the partition as ``reserved''.
Since the first sector always contains the FAT parameter block,
this really marks the nresrv-1 sectors starting at sector 1 as
``reserved''. When formatting the 9fat partition, -r 2 should
be used to jump over the partition table sector.
Again under -d, any files listed are added, in order, to the root
directory of the FAT file system. The files are contiguously allo‐
cated. If a file is named 9load, it will be created with the SYSTEM
attribute set so that dossrv(4) keeps it contiguous when modifying it.
Format checks for a number of common mistakes; in particular, it will
refuse to format a 9fat partition unless -r is specified with nresrv
larger than two. It also refuses to format a raw sd(3) partition that
begins at offset zero in the disk. (The beginning of the disk should
contain an fdisk partition table with master boot record, not a FAT
file system or boot block.) Both checks are disabled by the -x option.
The -v option prints debugging information.
The file /Inferno/386/pbs is an example of a suitable bfile to make the
disk a boot disk. It gets loaded by the BIOS at 0x7C00, reads the root
directory into address 0x7E00, and looks at the first root directory
entry. If that file is called 9LOAD, it uses single sector reads to
load the file into address 0x10000 and then jumps to the loaded file
image. The file /Inferno/386/pbslba is similar, but because it uses
LBA addressing (not supported by all BIOSes), it can access more than
the first 8.5GB of the disk.
Mbr installs a new boot block in sector 0 (the master boot record) of a
disk such as /dev/sdC0/data. This boot block should not be confused
with the boot block used by format, which goes in sector 0 of a parti‐
tion. Typically, the boot block in the master boot record scans the PC
partition table to find an active partition and then executes the boot
block for that partition. The partition boot block then loads a boot‐
strap program such as 9load(10.8), which then loads the operating sys‐
tem. If MS-DOS or Windows 9[58] is already installed on your hard
disk, the master boot record already has a suitable boot block. Other‐
wise, /Inferno/386/mbr is an appropriate mbrfile. It detects and uses
LBA addressing when available from the BIOS (the same could not be done
in the case of pbs due to space considerations). If the mbrfile is not
specified, a boot block is installed that prints a message explaining
that the disk is not bootable. The -9 option initialises the partition
table to consist of one plan9 partition which spans the entire disc
starting at the end of the first track.
EXAMPLES
Initialize the kernel disk driver with the partition information from
the FAT boot sectors. If Plan 9 partitions exist, pass that partition
information as well.
for(disk in /dev/sd??) {
if(ftest -f $disk/data && ftest -f $disk/ctl){
disk/fdisk -p $disk/data >$disk/ctl
}
for(part in $disk/plan9*){
if(ftest -f $part){
disk/prep -p $part >$disk/ctl
}
}
}
Create a boot floppy on a previously formatted diskette:
disk/format -b /Inferno/386/pbs -df /dev/fd0disk /Inferno/386/9load /tmp/plan9.ini
Initialize the blank hard disk /dev/sdC0/data.
disk/mbr -m /Inferno/386/mbr /dev/sdC0/data
disk/fdisk -baw /dev/sdC0/data
disk/prep -bw -a^(9fat fs) /dev/sdC0/plan9
disk/format -b /Inferno/386/pbslba -d -r 2 /dev/sdC0/9fat 9load 9pcdisk plan9.ini
SOURCE
/appl/cmd/disk/prep
/appl/cmd/disk/format.b
/os/boot/pc
SEE ALSOfloppy(3), sd(3), 9load(10.8), plan9.ini(10.8)
BUGS
Format can create FAT12 and FAT16 file systems, but not FAT32 file sys‐
tems. The boot block can only read from FAT12 and FAT16 file systems.
PREP(8)
