ChorusOS man pages section 7S: Devices

ram_disk(7s)

NAME | DESCRIPTION | ATTRIBUTES | SEE ALSO

NAME

RAM Disk- RAM disk partition table

DESCRIPTION

You can use RAM to house a file system.

To use RAM to house a file system, you must first label part of the available space using disklabel(1M). disklabel uses entries in disktab(4CC) to label the disk. The following disktab entry serves to label a 4 megabyte area of RAM as a disk:

# This label can be used for a 4 megabyte RAM disk. 
# The corresponding
# newfs command to be used with this RAM disk is:
# rsh target newfs -o space -c 26 -m 0 /dev/rd0a

rd4MegBSD:\
	:ns#32:nt#1:nc#256 \
	:pa#8192:oa#0:ta=4.2BSD:ba#8192:fa#8192 \
	:pc#8192:oc#0:tc=unused:

The default system initialization file, sysadm.ini(4CC), creates special files to access the RAM, so you probably do not need to create them yourself. The entries to create special files may appear as follows in sysadm.ini:

# Create special files for RAM disk
mknod /dev/rrd0a c 13 0
mknod /dev/rrd0b c 13 1
mknod /dev/rrd0c c 13 2
mknod /dev/rd0a  b 13 0
mknod /dev/rd0b  b 13 1
mknod /dev/rd0c  b 13 2

The above example creates both raw and block mode special files for two user-accessible partitions, a and b, and one partition, c, for use by the system only.

Assuming the special files exist, you can proceed to label the disk and so forth. The following commands label the disk, read the label, create a file system on the disk and check the file system:

$ rsh target disklabel -w -r rd0 rd4MegBSD
$ rsh target disklabel -r rd0
# /dev/rrd0c:
type: unknown
disk: rd16Meg
label: 
flags:
bytes/sector: 512
sectors/track: 4
tracks/cylinder: 4
sectors/cylinder: 16
cylinders: 32768
rpm: 3600
interleave: 1
trackskew: 0
cylinderskew: 0
headswitch: 0		# milliseconds
track-to-track seek: 0	# milliseconds
drivedata: 0 

3 partitions:
#      size  offset fstype   [fsize bsize   cpg]
a:    32768    0    4.2BSD      0     0     0 	# (Cyl.    0 - 2047)
c:    32768    0    unused      0     0       	# (Cyl.    0 - 2047)
$ rsh target newfs /dev/rd0a
/dev/rrd0a:	32768 sectors in 8 cylinders of 1 tracks, 4096 sectors
	16MB in 1 cyl groups (16 c/g, 32MB/g, 7680 i/g)
super-block backups (for fsck -b #) at:
 32,
$ rsh target fsck -y /dev/rd0a
** /dev/rrd0a
** Last Mounted on 
** Phase 1 - Check Blocks and Sizes
** Phase 2 - Check Pathnames
** Phase 3 - Check Connectivity
** Phase 4 - Check Reference Counts
** Phase 5 - Check Cyl groups
1 files, 1 used, 15390 free (14 frags, 1922 blocks, 0.1% fragmentation)

Once you have checked the new file system and it is ready to use, mount it in the current file system hierarchy. As the current root file system is located on the host workstation, create the mount point on the host and then mount the RAM file system there:

$ cd target_root_dir
$ mkdir ram
$ rsh target mount -t ufs /dev/rd0a /ram
/dev/rd0a on /ram

Next, populate the RAM file system with the contents of all file systems except the /dev, /image, /tmp and /ram directories. Create mount points for the /dev, /image and /tmp file systems:

$ rsh target  cp -R bin etc lib ram/
$ rsh target  mkdir /ram/dev
$ rsh target  mkdir /ram/image
$ rsh target  mkdir /ram/tmp

The RAM file system, mounted under the /ram directory, now contains everything needed to serve as the main system disk. Take advantage of the fact that the mount command is built into the C_INIT system actor.

Unmount the root file system.

The following commands unmount the root file system on the target and remount the RAM file system in its place:

$ rsh target umount /ram
$ rsh target umount /
$ rsh target mount -t ufs /dev/rd0a /
$ rsh target fsck /dev/rrd0a
$ rsh target mount -t ufs -o update /dev/rd0a /

The target is now independent of the host, using the RAM disk as the main disk:

$ rsh target ls
bin             dev             etc             image           lib
tmp

Note that the ls actor used above is located in the RAM disk file system.

The following script is meant to run on the host workstation (or other system) and summarizes the above scenario:

#! /sh

#
# Reboot the target and give it some time to come up.
#
rsh target reboot
sleep 60
# 
# While the host 'sleeps', the target downloads the system image, and
# executes system initialization commands in sysadm.ini, mounting
# the root file system through NFS.
#

#
# Label the RAM disk, then create the file system and check it.
#
rsh target  disklabel -w -r rd0 rd16Meg MyRamDisk
rsh target  newfs /dev/rrd0a
rsh target  fsck -y /dev/rrd0a

#
# Mount the RAM file system and populate it with the rest of the root
# directory.
#
rsh target mount -t ufs /dev/rd0a /ram
rsh target cp -R bin etc lib ram/
rsh target mkdir /ram/dev
rsh target mkdir /ram/image
rsh target mkdir /ram/tmp

#
# Unmount everything, then mount the RAM file system at the root.
#
rsh target umount /ram
rsh target umount /
rsh target mount -t ufs /dev/rd0a /
rsh target fsck /dev/rrd0a
rsh target mount -t ufs -o update /dev/rd0a /

After adapting the above script for your environment, run it to make your ChorusOS target self-sufficient.

The RAM disk slices can be as follows:

Note -

RAM disks x=0,1,2,3,4,5,6,7,8,9,a,b,c,d,e,f

				Major Minor
	/dev/rdxa		14    0 + 8 * x
	/dev/rdxb		14    1 + 8 * x
	/dev/rdxc		14    2	+ 8 * x	# Whole disk
	/dev/rdxd		14    3 + 8 * x
	/dev/rdxe		14    4 + 8 * x
	/dev/rdxf		14    5 + 8 * x
	/dev/rdxg		14    6 + 8 * x
	/dev/rdxh		14    7 + 8 * x

	/dev/rrdxa	13    0 + 8 * x
	/dev/rrdxb	13    1 + 8 * x
	/dev/rrdxc	13    2	+ 8 * x	# Whole disk
	/dev/rrdxd	13    3 + 8 * x
	/dev/rrdxe	13    4 + 8 * x
	/dev/rrdxf	13    5 + 8 * x
	/dev/rrdxg	13    6 + 8 * x
	/dev/rrdxh	13    7 + 8 * x

ATTRIBUTES

See attributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPE	ATTRIBUTE VALUE
Interface Stability	Evolving