Block devices

Block devices

[David H. Lynch Jr.]

    Sometime recently it seems to have become possible to disable the
whole block device subsystem.
    Though in my tests I can't quit build with it disabled.

     Anyway, for an embedded device this might be appealing.
    how does this interact with initramfs and flash ?
   
    Can I boot an initramfs kernel without a block device ?
    Can I write a filesystem driver for a flash device that does not
require a block device ?
    Are their any examples of something even close ?

   

      







-- 
Dave Lynch 					  	    DLA Systems
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Re: Block devices

[Jamie Lokier]

Indraneel wrote:
> >     Can I write a filesystem driver for a flash device that does not
> > require a block device ?
> 
> AFAIK, for a flash file system you need a Block Device. But you can 
> write a character driver to access the flash without a Block Device.

I think JFFS2 (flash file system) does not require a block device.  If
you mount /dev/mtdblockN with JFFS2, it actually looks up the
corresponding MTD character device and uses that instead.  The same is
probably true of the other dedicated flash filesystems.

-- Jamie

Re: Block devices

[Indraneel]

David,
First things first. Don't post to multiple mailing lists at the same time.

David H. Lynch Jr. wrote:
>     Sometime recently it seems to have become possible to disable the
> whole block device subsystem.

Yes it is possible. Works for me on 2.6.22-rc5.

>     Though in my tests I can't quit build with it disabled.
> 
>      Anyway, for an embedded device this might be appealing.
>     how does this interact with initramfs and flash ?
>    
>     Can I boot an initramfs kernel without a block device ?

Yes this is also possible. And that's why initramfs is fast.

>     Can I write a filesystem driver for a flash device that does not
> require a block device ?

AFAIK, for a flash file system you need a Block Device. But you can 
write a character driver to access the flash without a Block Device.

>     Are their any examples of something even close ?

  drivers/mtd/mtdchar.c

Regards,
Indro

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Re: Block devices

[Christoph Hellwig]

On Thu, Feb 21, 2008 at 02:05:52AM -0500, David H. Lynch Jr. wrote:
>     Can I boot an initramfs kernel without a block device ?

Yes.

>     Can I write a filesystem driver for a flash device that does not
> require a block device ?

Yes.

>     Are their any examples of something even close ?

For that particular flash case there's just jffs2 in the kernel tree,
with some more flash filesystems under development.  You can of
course have network and in-memory filesystems aswell.