Re: mount ramdisk rootfs /etc directory to jffs2 filesystem.

[Johnny Hung <johnny.hacking@gmail.com>]

2010/1/19 Matthias Kaehlcke <matthias@kaehlcke.net>:
> El Tue, Jan 19, 2010 at 06:13:07PM +0800 Johnny Hung ha dit:
>
>> 2010/1/19 Matthias Kaehlcke <matthias@kaehlcke.net>:
>> > El Tue, Jan 19, 2010 at 05:20:53PM +0800 Johnny Hung ha dit:
>> >
>> >> I have build an embedded Linux system and rootfs is a ramdisk. Ramdisk
>> >> rootfs resides in memory so modify files is non-effective after a
>> >> reboot. Some directories in rootfs, like /etc, /usr, ... are contain
>> >> many application configuration files and I want to mount it to jffs2
>> >> flash filesysyem so it will take effect after a reboot. Is it
>> >> possible?
>> >
>> How to do it? The ramdisk rootfs is ext2 filesystem and I try,
>> mount /mnt/mtd/etc /etc
>>
>> Try to modify /etc/ files is not works.
>
> ok, i understood you want to substitute the ramdisk rootfs by jffs2
> based one
>
> mounting the ramdisk as writable with the flash as backing storage
> isn't possible AFAIK. and even if it was possible it wouldn't be
> recommended as ext2 doesn't care about flash wear out, in consequence
> you would write the same blocks over and over again.
>
>> > yes, this is possible
>> >
>> >> I know the flash has write times limited so the log files
>> >> (syslogd/klogd) should not store in flash. In general, how to deploy
>> >> root file system for embedded linux with flash storage?
>> >
>> > - add jffs2 support to your kernel
>> > - create your image using mkfs.jffs2 from mtd-utils
>> > - flash the image
>> > - specify the rootfs partition and type in the bootargs of the kernel
>> The above procedure is to create a jffs2 rootfs image but I  prefer to
>> use ramdisk rootfs.
>> I think the rootfs is build as ramdisk and some configurable file is
>> store in jffs2 flash.
>

Okay, I think the steps is below if my rootfs is ramdisk and configure
files in jffs2,

1. cp /etc/* /mnt/mtd/etc/    (/mnt/mtd is my jffs2 fs)
2. rm -rf /etc/*
3. make symbolic links from all /etc/xx to /mnt/mtd/etc/xxx
4. remake ramdisk rootfs

It seems all files in ramdisk rootfs /etc all links to /mnt/mtd/etc/
and try to modify these files is effective after reboot.
But is this a common way in embedded linux ?

I also have another idea, keep ramdisk rootfs /etc files and add a shell script.

1. The shell script execute when system boot up.
2. Check /mnt/mtd/etc/xxx if is exist. If yes, remove /etc/xxx file
and make a symbolic link to /mnt/mtd/etc/xxx. If no, keep /etc/xxx
file.
3. repeat 2 for all /etc files

Any suggestion?

Thank your help.
BRs, H. Johnny

> in this case follow the above steps, except the last one about the
> bootargs and mount the jffs2 partition from your init script. you
> could use symlinks from your ramdisk to the files on jffs2 to
> integrate them in your rootfs
>
> --
> Matthias Kaehlcke
> Embedded Linux Developer
> Barcelona
>
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