Re: Mounting a in-ROM filesystem efficiently

[Bradley D. LaRonde]

I have maintained, on and off, a patch to crafms that supports traditional
cramfs decompress-and-read/run-from-RAM, plus direct mmaping with no
decompression and read/run straight out of ROM:

    http://www.ltc.com/~brad/mips/cramfs-linear-root-xip-linux-2.4.9-2.diff

It includes a modification to mkcramfs to compress or not compress
individual files based on their +t mode setting.  Mkcramfs will leave +t
uncompressed in the cramfs image and cramfs will directly mmap them.

Please note that the patch is against 2.4.9.  I haven't tried to use it
since then.

Regards,
Brad

----- Original Message -----
From: "Thomas Capricelli" <[e-mail]>
To: <[e-mail]>
Sent: Thursday, December 13, 2001 11:02 AM
Subject: Mounting a in-ROM filesystem efficiently

>
>
> Hello,
>
> I'm looking for a way to put a filesystem into ROM.
> Seems pretty trivial, isn't it ?
>
> My understanding is (the way initrd does, and the way I do as of today)
> * create a RAMDISK
> * loads the data into ramdisk
> * mount the ramdisk
>
> problem is that I don't want to waste the RAM as the data in the ROM is
> already in the address space. (it's an embedded system, btw)
>
> Speed is not an issue here. ROM access might be slower than RAM, it will
> always be so much quicker than a disk access. (wrong?)
>
> Ideally, i would give address/length of the fs in ROM to a function, and I
> would get a ramdisk configured to read its data exactly there, and not in
> ram.
>
> Any hint ?
>
> I've tried to look in the different options from mainstream kernels and
> embedded-oriented kernels whithout success.
>
>
> thanx,
> Thomas
> ps : i'm subscribed to lkml, no need to cc:
>
> --
> Thomas Capricelli <[e-mail]>
> boson.eu.org, kvim, zetalinux-
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