Re: journaling filesystem

David Woodhouse (
Fri, 15 May 1998 12:29:19 +0200 said:
> I have now 4MB of SUNW,nvtwo NVRAM in SS1000 and 2MB of SUNW,nvone in
> SS20, both running Linux. I hope to write a driver soon and then we
> could do metadata logging onto those NVRAMs. BTW: Aren't there any
> similar NVRAM cards or SIMMs for PCs these days, so that it could be a
> more general solution than for one single port?

There are ISA Flash ROM cards available, certainly. I've seen sizes up to 8Mb,
possibly 16.

I put together a driver for them. It's the basics of a generic memory device
subsystem, with support for multiple hardware devices, and multiple high-level
applications on top of them.

It's at

Low level drivers I have are a simple one to use physical memory above the
range used for Linux (boot with "mem=64Mb" and use the rest as a memory
device), and one for the ISA flash card I was developing with.

High level drivers are: a character device, an FTL translation layer device,
for the filing systems you'll generally find on such hardware, and a raw block

It's based on the memory device subsystem in the PCMCIA drivers, and
development was suspended after discussion with David Hinds about separating
the PCMCIA memory device subsystem so that it could apply to both, rather than
forcing me to re-invent it all. But then I got put onto other projects, and
it's been left alone since then.

Documentation is sparse, for which read non-existent. Compile the modules with
the same command line that your kernel modules get compiled with.
mtd.o is the generic memory technology device support module, which provides
character device for each device present.
physmem.o and flashcard.o are the low level drivers.
ftl.o provides a block device for each physical device present with a valid
FTL filesystem on it, and also implements partition table support.

I can't see the basic block device implementation, so either I'm lying about
having written it, or it's also included in mtd.c - your guess is as good as
mine by this time ;)

Happy Hacking.

---- ---- ----
David Woodhouse, Robinson College, CB3 9AN, England. (+44) 0976 658355
finger for PGP key.

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