linux-kernel - Re: [PATCH 2.6.24] block2mtd: removing a device and typo fixes

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Message-ID: <chaz20080220173053.GX4539@artesyncp.com>
Date:	Wed, 20 Feb 2008 17:30:53 +0000
From:	Stephane Chazelas <stephane.chazelas@...rson.com>
To:	Jörn Engel <joern@...fs.org>
Cc:	Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
	linux-mtd@...ts.infradead.org
Subject: Re: [PATCH 2.6.24] block2mtd: removing a device and typo fixes

2008-02-20 18:22:50 +0100, Jörn Engel:
> On Wed, 20 February 2008 17:02:31 +0000, Stephane Chazelas wrote:
> > 
> > sorry, I wasn't very clear.
> > 
> > With "loop", you're doing an ioctl() to /dev/loop<x> so that
> > /dev/loop<x> become a block device associated with a given file.
> > 
> > Applying that strictly to block2mtd wouldn't make sense.
> > 
> > At the moment, when you create a new block2mtd, the only thing
> > you see is an entry in /proc/mtd.
> > 
> > You don't access that mtd device directly (there's no
> > /dev/mtd<x>). Instead, you may access it via a /dev/mtdblock<x>
> > if you have "block2mtd" for instance.
> 
> Actually, there is /dev/mtd<x>.  Enable CONFIG_MTD_CHAR.

Yes, my point ;). "block2mtd" creates a "mtd" out of a block
device and "mtdchar" and "mtdblock" create the "char" and
"block" devices out of the "mtd". This is a different concept
from "loop". With "loop", you make a block device out of a file,
but you do the ioctl on the target loop block device itself.
With block2mtd, you can't do that.

> > Here, what you need, is an API that gets a block device (with fd
> > or path) and an erase size and that returns a mtd identifier.
> 
> Erase size is a real difference, agreed.  Otherwise the loop analogy is
> quite good.  Occasionally people are asking for file->mtd translation as
> well.
[...]

Actually, that's what I use block2mtd for, in combination with
"loop" to mount jffs2 filesystem images (always wondered if
there wasn't a simpler way, BTW (other than mtdram))

Cheers,
Stephane
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