[LEDE-DEV] [RFC] rootfs_data on different MTD outside firmware image

[Daniel Golle]

Hi Adrian,


On Fri, Jun 17, 2016 at 11:21:07PM -0500, Adrian Panella wrote:
> Hi, some Linksys devices (i.e WRT1900AC, EA4500, EA8500,...) have two
> different partitions for dual boot, and an additional partition that Linksys
> uses for system config (sysconf).
> Each of these partitions is of a considerable size (23-37 mb, varying
> between devices).
> 
> As far as I could see, the ports already in Owrt/LEDE (Kirkwook & Mvebu) use
> only one partition at a time for the overlayfs, so total 23-37mb shared
> among squashfs rom and ubifs overlay.
> In some cases the third partition (sysconf) is mounted, but in /mmt, not
> taking part in the overlay, and so not directly useful for installing
> additional packages.
> 
> I believe that a way to better profit all this available space would be to
> leave one partition for the rom squashfs alone (23-37mb there) and share the
> 3rd partition between alternative boots as the ubifs overlay (another
> 23-37mb here). In total we double the space up to a full 74mb for packages,
> reducing the need for extroot.
> 
> 
> Have you found any serious disadvantage on this approach, and that's why it
> is not implemented in mvebu/kirkwood? If so, which one?

John explained that in another reply to your mail.

> 
> If we leave ubifs outside the image, and only squash in one MTD, does it add
> any benefit to have squash image on top of an UBI layer? Erase counters
> would be lost between firmware flashes anyway and no other write would occur
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

NACK. As we do ubiupdatevol for sysupgrade, the erase counters will be
preserved. Even ubiformat would preserve them, and we never write to
ubi-formatted NAND in any other way than either using ubiformat or
ubiupdatevol.

> in between. On the other hand, in the third MTD (i.e. sysconf) the erase
> counters could be preserved between firmware updates, as the ubi block
> doesn't need to be recreated each time, and only a ubiformat could be
> performed on flash.

I don't get what you are talking about.


Cheers


Daniel


> 
> I'm planning on switching ipq806x/EA8500 to this scheme, and would
> appreciate opinions first.
> 
> 
> 
> 
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