Re: ubiblock RW

Ezequiel Garcia
2016-03-24T21:27:08Z

On 24 March 2016 at 17:38, Richard Weinberger <richard@nod.at> wrote:
> Hi!
>
> Am 24.03.2016 um 15:23 schrieb Ezequiel Garcia:
>> +MTD
>>
>> On 23 March 2016 at 14:40, Benson Young <benson6877@gmail.com> wrote:
>>> Hello Ezequiel,
>>>
>>> I came upon the discussion about block device emulation over UBI.
>>> http://linux-mtd.infradead.narkive.com/YF0XOFxY/block-device-emulation-on-top-of-ubi-volumes-with-read-write-support
>>>
>>> I understand the most recent implementation is read-only emulation for
>>> mounting squashfs based file system.
>>> However, I would really like to see the write option be brought back. If
>>> not, can you please help me about enabling the write option in my build?
>>> I have used the patch listed in the following link
>>> https://lwn.net/Articles/525957/
>>> but i couldn't find any accompanying util that allows me to create the ubi
>>> block volume.
>>>
>>
>> You should be able to use mtd-utils' ubiblock tool (maybe you'll need to do
>> some modifications).
>>
>> http://www.linux-mtd.infradead.org/doc/ubi.html#L_ubiblock
>>
>>> Reason for this request is that I am looking into root file system
>>> encryption over un-managed NAND flash. Now the mainline method of disk
>>> encryption in Linux revolves around
>>> dm-crypt module which requires a block device. i am under the impression
>>> that using mtdblock works to an extent until the partition you try to
>>> map/encrypt has bad blocks in it.
>>> I have seen discussion about using UBIFS, and I have seen a paper discussing
>>> it, where the author embeds the encryption engine within UBI layer, so each
>>> write and read is encrypted. However, its a path I would take when I have no
>>> choice. Right now dm-crypt is my first choice basically because of the
>>> availability of support/discussion/information.
>>>
>>> I also saw you mentioned that you don't have NAND flash for testing, this is
>>> something that I can help with. I have an abundance of NAND flash devices.
>>
>> I have some devices with SLC NANDs now, but thanks for the offer.
>>
>>> For simplicity sake, I work with SLC because of better endurance compared to
>>> MLC. I am also curious about flash endurance with EXT4 over UBI. Destructive
>>> erase/write will definitely on my to-do list.
>>>
>>
>> So, like I said here:
>>
>> http://linux-mtd.infradead.narkive.com/YF0XOFxY/block-device-emulation-on-top-of-ubi-volumes-with-read-write-support
>>
>> We can definitely implement write support if we have a good use case for it.
>> Encryption might be one.
>>
>> Richard, what do you think?
>
> I'm definitely not fond of adding write support to ubiblock without turning it into a proper FTL.
> Otherwise it will be abused and will cause serious damage.
>

I'm not sure this statement makes much sense without actual numbers.

Of course, eraseblocks will be erased much more often with a regular
block-oriented
filesystem. But a user could agressively control write access and prevent this.

Would it be that bad to add write support and add some big warning to
prevent users about potential damage?

--
Ezequiel García, VanguardiaSur