jffs2 usage question: nandwrite

jffs2 usage question: nandwrite

[K Richard Pixley]

I'm a newbie to flash file systems and I've spent my day reading. 
However, I seem to be missing something.

Several sets of instructions encourage me to build my file system using 
mkfs.jffs2, which I understand creates an image, (akin to mkisofs), 
rather than operating on a device file.  However, once I have the image, 
they recommend placing the image onto flash using nandwrite.

I can't find any doc on nandwrite, but I'm guessing that it does a "bad 
block aware" sequential copy, meaning that it simply skips any blocks 
that it recognizes as bad according to a manufacturer mark. Assuming so, 
doesn't this hole in my fresh jffs2 file system cause jffs2 grief?  I 
mean, it would cause most other file systems grief to have an extra 
block inserted in the middle of their block sequence.

What am I missing?

--rich

RE: jffs2 usage question: nandwrite

[Iwo Mergler]

Hi Rich,


JFFS2 keeps all the relevant information in every block. That is, you can shuffle
the erase blocks any way you like and you still have a valid file system.

The holes made by skipping bad blocks are not a problem.


Best regards,

Iwo

________________________________________
From: linux-mtd [linux-mtd-bounces@lists.infradead.org] On Behalf Of K Richard Pixley [rpixley@graphitesystems.com]
Sent: Friday, 7 November 2014 1:47 PM
To: linux-mtd@lists.infradead.org
Subject: jffs2 usage question: nandwrite

I'm a newbie to flash file systems and I've spent my day reading.
However, I seem to be missing something.

Several sets of instructions encourage me to build my file system using
mkfs.jffs2, which I understand creates an image, (akin to mkisofs),
rather than operating on a device file.  However, once I have the image,
they recommend placing the image onto flash using nandwrite.

I can't find any doc on nandwrite, but I'm guessing that it does a "bad
block aware" sequential copy, meaning that it simply skips any blocks
that it recognizes as bad according to a manufacturer mark. Assuming so,
doesn't this hole in my fresh jffs2 file system cause jffs2 grief?  I
mean, it would cause most other file systems grief to have an extra
block inserted in the middle of their block sequence.

What am I missing?

--rich

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RE: jffs2 usage question: nandwrite

[Ricard Wanderlof]

On Fri, 7 Nov 2014, Iwo Mergler wrote:

> JFFS2 keeps all the relevant information in every block. That is, you 
> can shuffle the erase blocks any way you like and you still have a valid 
> file system.
> 
> The holes made by skipping bad blocks are not a problem.

Additionally, JFFS2 is bad-block-aware, so it knows that there can be bad 
blocks in a partition on which a file system is mounted, and avoids trying 
to use them.

/Ricard
-- 
Ricard Wolf Wanderlöf                           ricardw(at)axis.com
Axis Communications AB, Lund, Sweden            www.axis.com
Phone +46 46 272 2016                           Fax +46 46 13 61 30