Ramdisk Root

QNX Newsgroups (Archives) qdn.public.qnxrtp.os
1

Hello, all,

Is it possible to use a ramdisk as root? I am booting from a disk on
chip, and want to copy or untar its contents onto a ramdisk, then use
that ramdisk as root. However, I still need access to the disk on
chip, in order to save changes to config files.

Thanks,
Kevin

–
He that breaks a thing to find out what it is has left the path of
wisdom – Gandalf the Grey

2

sure.
neutrino supports union filesystems so the last filesystem to mount will
be written to first. this can be confusing…

what i prefer to do is to mount a ramdisk as /ram and then make symlinks
to specific directories within it. that way i know where things are
going.

for fun, try this … but again, this can get confusing…:

devf-ram -s0,4M & # for a 4M ramdisk

flashctl -p /dev/fs0p0 -e -f -n / -m

now you are mounted as root.
create any new file in / … it will go to the ramdisk.

slay devf-ram

the new files you created are gone.

what fun!!

Kevin Lacquement <klacquement@syscor.com> wrote:

Hello, all,

Is it possible to use a ramdisk as root? I am booting from a disk on
chip, and want to copy or untar its contents onto a ramdisk, then use
that ramdisk as root. However, I still need access to the disk on
chip, in order to save changes to config files.

Thanks,
Kevin

–
He that breaks a thing to find out what it is has left the path of
wisdom – Gandalf the Grey

–
Randy Martin randy@qnx.com
Manager of FAE Group, North America
QNX Software Systems www.qnx.com
175 Terence Matthews Crescent, Kanata, Ontario, Canada K2M 1W8
Tel: 613-591-0931 Fax: 613-591-3579

3

Hi Randy,

This is interesting. I’ve been re-prefixing the root directory ‘/’ on QNX 4
for years. But this works quite nicely. Can you define union file systems
any better. Is it simply that the most recent process that claims that name
space prefix wins?

–

–
Bill Caroselli - Sattel Global Networks
1-818-709-6201 ext 122



“Randy Martin” <randy@qnx.com> wrote in message
news:9f6b5n$hif$2@nntp.qnx.com…

sure.
neutrino supports union filesystems so the last filesystem to mount will
be written to first. this can be confusing…

what i prefer to do is to mount a ramdisk as /ram and then make symlinks
to specific directories within it. that way i know where things are
going.

for fun, try this … but again, this can get confusing…:

devf-ram -s0,4M & # for a 4M ramdisk

flashctl -p /dev/fs0p0 -e -f -n / -m

now you are mounted as root.
create any new file in / … it will go to the ramdisk.

slay devf-ram

the new files you created are gone.

what fun!!

Kevin Lacquement <> klacquement@syscor.com> > wrote:
Hello, all,

Is it possible to use a ramdisk as root? I am booting from a disk on
chip, and want to copy or untar its contents onto a ramdisk, then use
that ramdisk as root. However, I still need access to the disk on
chip, in order to save changes to config files.

Thanks,
Kevin

–
He that breaks a thing to find out what it is has left the path of
wisdom – Gandalf the Grey

–
Randy Martin > randy@qnx.com
Manager of FAE Group, North America
QNX Software Systems > www.qnx.com
175 Terence Matthews Crescent, Kanata, Ontario, Canada K2M 1W8
Tel: 613-591-0931 Fax: 613-591-3579

4

“RM” == Randy Martin <> randy@qnx.com> > writes:

[…]

RM> what i prefer to do is to mount a ramdisk as /ram and then
RM> make symlinks to specific directories within it. that way i
RM> know where things are going.

This will probably be easier; that’s sort of what I’m doing right now.

[…]

RM> now you are mounted as root.
RM> create any new file in / … it will go to the ramdisk.

How can I get the new/edited files to go to the original filesystem?

Cheers,
Kevin

–
He that breaks a thing to find out what it is has left the path of
wisdom – Gandalf the Grey

5

Bill Caroselli <Bill@sattel.com> wrote:

Hi Randy,

This is interesting. I’ve been re-prefixing the root directory ‘/’ on QNX 4
for years. But this works quite nicely. Can you define union file systems
any better. Is it simply that the most recent process that claims that name
space prefix wins?

–
Bill Caroselli - Sattel Global Networks
1-818-709-6201 ext 122

Take a look at the Neutrino System Architecture Guide as well as the
documentation for resmgr_attach() where it describes the behaviour
of the _RESMGR_FLAG_DIR, _RESMGR_FLAG_BEFORE, _RESMGR_FLAG_AFTER,
_RESMGR_FLAG_OPAQUE flags.

Also take a look at the name resolution process:

http://staff.qnx.com/~thomasf/nto.html → QNX2000 Open PPT stuff


Thomas

“Randy Martin” <> randy@qnx.com> > wrote in message
news:9f6b5n$hif$> 2@nntp.qnx.com> …
sure.
neutrino supports union filesystems so the last filesystem to mount will
be written to first. this can be confusing…

what i prefer to do is to mount a ramdisk as /ram and then make symlinks
to specific directories within it. that way i know where things are
going.

for fun, try this … but again, this can get confusing…:

devf-ram -s0,4M & # for a 4M ramdisk

flashctl -p /dev/fs0p0 -e -f -n / -m

now you are mounted as root.
create any new file in / … it will go to the ramdisk.

slay devf-ram

the new files you created are gone.

what fun!!

Kevin Lacquement <> klacquement@syscor.com> > wrote:
Hello, all,

Is it possible to use a ramdisk as root? I am booting from a disk on
chip, and want to copy or untar its contents onto a ramdisk, then use
that ramdisk as root. However, I still need access to the disk on
chip, in order to save changes to config files.

Thanks,
Kevin

–
He that breaks a thing to find out what it is has left the path of
wisdom – Gandalf the Grey

–
Randy Martin > randy@qnx.com
Manager of FAE Group, North America
QNX Software Systems > www.qnx.com
175 Terence Matthews Crescent, Kanata, Ontario, Canada K2M 1W8
Tel: 613-591-0931 Fax: 613-591-3579

–

Thomas (toe-mah) Fletcher QNX Software Systems
thomasf@qnx.com Neutrino Development Group
(613)-591-0931 http://www.qnx.com/~thomasf

6

Kevin Lacquement <klacquement@syscor.com> wrote:

“RM” == Randy Martin <> randy@qnx.com> > writes:

[…]

RM> what i prefer to do is to mount a ramdisk as /ram and then
RM> make symlinks to specific directories within it. that way i
RM> know where things are going.

This will probably be easier; that’s sort of what I’m doing right now.

[…]

RM> now you are mounted as root.
RM> create any new file in / … it will go to the ramdisk.

How can I get the new/edited files to go to the original filesystem?

i honestly do not know. i have not had to try that… maybe others can
comment. i would not build a system based on that model though… just my
personal opinion.
if you are trying to solve a redundancy problem, then a possible solution is
to build a simple resmgr that takes over a portion of the namespace and
responds to opens. it can redirect opens to other mountpoints.
the ‘inflator’ program does something like this (sits in front and checks
for a compression signature on any open for any file in its mountpath(s))

–
Randy Martin randy@qnx.com
Manager of FAE Group, North America
QNX Software Systems www.qnx.com
175 Terence Matthews Crescent, Kanata, Ontario, Canada K2M 1W8
Tel: 613-591-0931 Fax: 613-591-3579

7

“RM” == Randy Martin <> randy@qnx.com> > writes:

[…]

RM> if you are trying to solve a redundancy problem, then a possible solution is
RM> to build a simple resmgr that takes over a portion of the namespace and
RM> responds to opens. it can redirect opens to other mountpoints.
RM> the ‘inflator’ program does something like this (sits in front and checks
RM> for a compression signature on any open for any file in its mountpath(s))

Thanks. I’ll take a look at trying that.

–
He that breaks a thing to find out what it is has left the path of
wisdom – Gandalf the Grey