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SubjectRe: Mounting a in-ROM filesystem efficiently
Followup to:  <>
By author: Thomas Capricelli <>
In newsgroup:
> 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?)

Frequently wrong. Depending on the interface, ROM can be just
unbelievably slow.

> 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.

The right thing for you to do is to write a block device driver, and
then mount that block device like any order device. Your in-use data
will be copied to RAM (i.e. cached), but it can be dropped and
re-fetched as necessary. This should be the desired behaviour.

<> at work, <> in private!
"Unix gives you enough rope to shoot yourself in the foot." <>
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