Very Computer

I am just finishing off development of an embedded system but I'm having
a bit of a problem with an ATA Flash disk that I'm trying to use.

Everything is fine with it, except I want to mount it in Read Only mode
to prevent killing the flash media. I have read a few articles on this
and they seem to imply the following sequence of events:

(1)     Use initrd to load a small kernel image
(2)     Write a linuxrc script to zcat a root file system onto a ram disk
        with links to the permanent files on the flash disk
(3)     mount the flash disk as read only, say in the /mnt directory
(4)     unmount the ram disk and exit the linuxrc script so initrd can
        remount it and continue the boot sequence.

All sounds relatively easy and, to this end, I did the following:

(1)     Made up a small kernel image (mkinitrd) and used zcat to unpack it
        onto a ram disk
(2)     Edited the /etc/fstab to mount /dev/ram as root file system
(3)     Edited linuxrc to the following:
                #!/bin/sash
                aliasall

                # This mounts the flash card into /mnt
                mount -t minix /dev/hdc1 /mnt

                # This is unnecessary but I'm doing it just to make sure
                mkfs.minix /dev/ram 2000

                # Extract the new root file system to the ram disk
                zcat /mnt/boot/rootfs.img.gz >/dev/ram

                # Now unmount the flash disk
                umount /dev/hdc1

                # Just for testing purposes mount the ram disk and do
                # a directory listing
                mount -t minix /dev/ram /mnt
                ls /mnt

                # unmount the ram disk (as initrd will re-mount it)
                umount /dev/ram

(4)     Copied extra executables / libraries into /bin and /lib as
        determined using ldd

I have traced this every step of the way and cannot work out what is
going wrong. The final "ls /mnt" command shows me that the ram disk is
empty... despite having unpacked a file into it.
I am 99.9% sure that the zcat line is not doing anything although I
can't determine why it doesn't report any errors (yes, tried 2>
error.file).

Things I have checked:
(1)     "zcat -h" in linuxrc DOES produce help text on screen so its not
        simply that it can't find the executable.
(2)     rootfs.img.gz IS a valid zcat file system, i.e. from a command
        line I CAN type "zcat rootfs.img.gz >/dev/ram" and it WILL create
        the file system.
(3)     I've tried simply copying the file "rootfs.img.gz" from the flash
        to the ram disk just to check I have made a valid ram disk and the
        mount is valid and that works just fine.

PLEASE PLEASE PLEASE! If anyone's done this I need an answer asap...I've
spent 3 days already trying to work out what's gone wrong!

Jeremy

But other than that I can't see anything wrong with what you're trying
to do I'm afraid :(

Phil

--
http://www.kantaka.co.uk/ .oOo. public key: http://www.kantaka.co.uk/gpg.txt

I get the impression that /dev/ram is already
mounted at this stage, since you unmount it
later. Randomly scribbling over a mounted
filesystem (even if you are replacing it with
a new valid filesystem) sounds like a bad
move to me.

What happens if you umount /dev/ram before this
step, then remount it afterwards?

    [...]

Quote:>                 # unmount the ram disk (as initrd will re-mount it)
>                 umount /dev/ram

Quote:> All sounds relatively easy and, to this end, I did the following:

> (1)        Made up a small kernel image (mkinitrd) and used zcat to unpack it
>    onto a ram disk
> (2)        Edited the /etc/fstab to mount /dev/ram as root file system
> (3)        Edited linuxrc to the following:
>            #!/bin/sash
>            aliasall

>            # This mounts the flash card into /mnt
>            mount -t minix /dev/hdc1 /mnt

>            # This is unnecessary but I'm doing it just to make sure
>            mkfs.minix /dev/ram 2000

>            # Extract the new root file system to the ram disk
>            zcat /mnt/boot/rootfs.img.gz >/dev/ram

>            # Now unmount the flash disk
>            umount /dev/hdc1

>            # Just for testing purposes mount the ram disk and do
>            # a directory listing
>            mount -t minix /dev/ram /mnt
>            ls /mnt

>            # unmount the ram disk (as initrd will re-mount it)
>            umount /dev/ram

> (4)        Copied extra executables / libraries into /bin and /lib as
>    determined using ldd

The entire procedure shown above seems to me a little odd. You are
actually trying to do by means of a script what the boot loader can do
better.

The usual boot process, in fact, first loads a kernel, then it can
optionally load a root filesystem possibly into a ram disk. The boot
device is not mounted in this process, so if you want it available when
the system is running, you must explicitly mount it (so you can mount it
readonly or even keep it unmounted for better protection).

You can find a lot of information on the entire process in the
Bootdisk-HOWTO, which is intended to give direction for booting from
diskettes, but can be applied to booting from other means, too.

Cheers,
                                                        l.f.
--------------------------------------------------------------------------
       -- )     Luca Fini                            Tel: +39 055 2752 307
 ___    |\      Osservatorio Astrofisico di Arcetri  Fax: +39 055 2752 292
/   |   | |-_   L.go E.Fermi, 5 +-----------------------------------------
(___|___//___)  50125 Firenze  /   WWW: http://www.arcetri.astro.it/~lfini

-----------------------------+--------------------------------------------

That was successful, I have interspersed regular "ls -l /" lines into my
linuxrc file to watch what the file system is doing from step to step of
my script and everything but the zcat was (is) working.

Jeremy

                # Just for testing purposes mount the ram disk and do
                # a directory listing
                mount -t minix /dev/ram /mnt
                ls /mnt

                # unmount the ram disk (as initrd will re-mount it)
                umount /dev/ram

The umount you are referring to is simply the unmount of the ram disk
that I "ls" to test if the file system had been built correctly. I know
the /dev/ram isn't mounted because if it was I would get an error at the
"mount -t minix /dev/ram /mnt" statement along the lines of "device
busy".

I will try a umount prior to the unpack... Nope, sorry no difference.

It's a bit of a problem that the sash mount command is unable to list
the currently mounted drives. I tried swapping to the full-blown mount
command but it requires mtab / fstab and other bits & pieces which I
didn't want to get into.

More suggestions guys?

Jem

I was actually working from Paul Moodys embedded device howto:

        http://www.linux-embedded.com/pmhowto.html

What he says is that you need to use initrd to load a root file system
which then expands a larger, say 40MB, ram disk from the flash disk and
continues the boot process.

However, what you are saying does make sense to me... I am going to have
to investigate this further. He (apparently) got everything to work (I
followed his howto step-by-step) but I can't get zcat to work at all and
am wondering how he did it.... And now I'm wondering WHY he did it ;-)

Jeremy

*snip*

Quote:>I was actually working from Paul Moodys embedded device howto:
>    http://www.linux-embedded.com/pmhowto.html
>What he says is that you need to use initrd to load a root file system
>which then expands a larger, say 40MB, ram disk from the flash disk and
>continues the boot process.
>However, what you are saying does make sense to me... I am going to have
>to investigate this further. He (apparently) got everything to work (I
>followed his howto step-by-step) but I can't get zcat to work at all and
>am wondering how he did it.... And now I'm wondering WHY he did it ;-)

You have to make sure all the details are right. I'm sure some of
this should be obvious, but for example you need to compile your
copies of zcat, mount, and any other programs you use in the
boot phase as *static* executables. You cannot have any dynamically
linked executables unless you are going to include the libs.
I just downloaded the source rpm's and compiled static.

--
        "Who needs horror movies when we have Microsoft"?
         -- Christine Comaford, PC Week, 27/9/95

Jeremy