Re: [RFC/PATCH 0/1] ubi: Add ubiblock driver

Shmulik Ladkani
2012-11-25T07:36:37Z

Hi Ezequiel,

On Sat, 24 Nov 2012 18:02:59 -0300 Ezequiel Garcia <elezegarcia@gmail.com> wrote:
> I've started working on a workload scenario to measure if ubiblock write
> is useful or just plain nonsense.

Please note eraseblock wear is just one aspect of using a standard r/w
filesystem over ubiblock.

There's another potential hazard of using r/w ubiblock, which is the
lack of power-cut tolerance.
Changing a file atomically in ubifs or jffs2 is tolerant to power
cuts (see [1]).
I'm not sure this is possible in ubiblock case, due to the 1-LEB
writeback cache: if a file (in the mounted fs) is synced, are there any
guarantees the 1-LEB cache is flushed synchronously?
(you mentioned the actual write is only done when a request arrives to
read or write to a different LEB or when the device is released).

> Since read-only ubiblock is less controversial, I'll post a read-only
> version of ubiblock (with an option to use a vmalloced
> buffer to cache reads?).
> We can add write support later, if it's not useless.
>
> Any thoughts?

Well I was about to suggest that approach :)
I would even split your patch further: the core stuff (with r/o
support), and an additional patch with all the DEBUG stuff. This may
ease reviewer's job.

Regards,
Shmulik

[1] http://www.linux-mtd.infradead.org/faq/ubifs.html#L_atomic_change