linux-kernel - Re: [PATCH 00/10] AXFS: Advanced XIP filesystem

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Message-ID: <6934efce0808210730y77db925cg263c957abb056fea@mail.gmail.com>
Date:	Thu, 21 Aug 2008 07:30:03 -0700
From:	"Jared Hulbert" <jaredeh@...il.com>
To:	carsteno@...ibm.com
Cc:	Linux-kernel@...r.kernel.org, linux-embedded@...r.kernel.org,
	linux-mtd <linux-mtd@...ts.infradead.org>,
	"Jörn Engel" <joern@...fs.org>,
	tim.bird@...sony.com, nickpiggin@...oo.com.au
Subject: Re: [PATCH 00/10] AXFS: Advanced XIP filesystem

> I like the general approach of it. It's much more flexible than the ext2
> extension I've done, and the possibility to select XIP vs. compression per
> page is really really neat. I can imagine that people will prefer this over
> the ext2 implementation on s390. It is unclear to me how the "secondary
> block device" thing is supposed to work. Could you elaborate a bit on that?

First off we don't yet support direct_access(), but I am planning on that soon.

Sure.  For a system that has say a NOR Flash and a NAND or a embedded
MMC, one can split a filesystem image such that only the XIP parts of
the image are on the NOR while the compressed bits are on the NAND /
eMMC.  The NOR part is accessed as directly addressable memory, while
the NAND would use mtd->read() and the eMMC would use block device
access API's.  In this case I would call this NAND or eMMC the
"secondary device" because the primary device is the NOR.

Assuming my NOR was at /dev//mtd2 and my NAND at /dev/mtd5.  I would
call the following to mount such a system:

mount -t axfs -o second_dev=/dev/mtd5 /dev/mtd2 /mnt/axfs
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