jffs on non-MTD device?

jffs on non-MTD device?

[Pavel Machek]

Hi!

I'm trying to run jffs on my ATA-flash disk (running ext2 could kill
some flash cells too soon, right?) but it refuses:

        if (MAJOR(dev) != MTD_BLOCK_MAJOR) {
                printk(KERN_WARNING "JFFS: Trying to mount a "
                       "non-mtd device.\n");
                return 0;
        }

What are reasons for this check?

								Pavel

-- 
I'm pavel@ucw.cz. "In my country we have almost anarchy and I don't care."
Panos Katsaloulis describing me w.r.t. patents at discuss@linmodems.org

Re: jffs on non-MTD device?

[David Woodhouse]

pavel@suse.cz said:
> I'm trying to run jffs on my ATA-flash disk (running ext2 could kill
> some flash cells too soon, right?) but it refuses:

CompactFlash does wear levelling internally. 

>         if (MAJOR(dev) != MTD_BLOCK_MAJOR) {
>                 printk(KERN_WARNING "JFFS: Trying to mount a "
>                        "non-mtd device.\n");
>                 return 0;
>         }

> What are reasons for this check? 

JFFS doesn't actually use the block device interface. Specifying it in the 
mount command is simply a hack to make life easier, which nobody's yet 
managed to obsolete. We actually use the underlying MTD device:

        mtd = get_mtd_device(NULL, MINOR(dev));

If you want JFFS (or JFFS2) on a CF device - in the apparent absence of any 
other relatively low overhead, compressing, journalling file system to use 
on it - then you need to provide a translation driver similar to the mtdram 
one which fakes an MTD device, using a block device as backing store.

--
dwmw2

Re: jffs on non-MTD device?

[Padraig Brady]

Some (most?) CF disks have hareware wareleveling.
I use ext2 with e2compr patch.

Padraig.

Pavel Machek wrote:

>Hi!
>
>I'm trying to run jffs on my ATA-flash disk (running ext2 could kill
>some flash cells too soon, right?) but it refuses:
>
>        if (MAJOR(dev) != MTD_BLOCK_MAJOR) {
>                printk(KERN_WARNING "JFFS: Trying to mount a "
>                       "non-mtd device.\n");
>                return 0;
>        }
>
>What are reasons for this check?
>
>								Pavel
>

Re: jffs on non-MTD device?

[David Woodhouse]

Padraig@AnteFacto.com said:
> Some (most?) CF disks have hareware wareleveling. I use ext2 with
> e2compr patch.

There are some who want a journalling filesystem on their CF device. 
Did anyone do e3compr yet? :)

Personally, I wouldn't bother with it - these things have a form of
pseudo-filesystem, probably similar to FTL or NFTL, implemented internally
to emulate a block device, and it's been reported that they don't do that
particularly well - they break down and lose data if you put them through
the kind of repeated power cycle tests that JFFS and JFFS2 have been
subjected to. A journalling filesystem on an unreliable medium is sort of 
pointless.

Far better to use a real flash device. But maybe I'm biased :)

--
dwmw2