Re: ubiblock RW

[Artem Bityutskiy <dedekind1@gmail.com>]

On Mon, 2016-03-28 at 00:01 +0200, Richard Weinberger wrote:
> Am 26.03.2016 um 07:01 schrieb Willy Tarreau:
> > 
> > On Fri, Mar 25, 2016 at 10:25:17PM +0100, Richard Weinberger wrote:
> > > 
> > > Am 25.03.2016 um 21:50 schrieb Ezequiel Garcia:
> > > > 
> > > > I guess we could have some UBI parameter to enable this
> > > > support,
> > > > and print a very noisy message to warn users about potential
> > > > device wear out -- naively assuming users read messages...
> > > As I wrote in my previous mail, I think a new parameter for the
> > > ubiblock
> > > tool would do the job.
> > > I'd default ubiblock to RO and via the ubiblock tool you can
> > > enable RW mode.
> > > ...which would also trigger a warning.
> > > 
> > > What I'd like to avoid is a kernel command line or a Kconfig
> > > option to make
> > > RW default. If someone *really* wants RW she has to run ubiblock
> > > --enable-rw....
> > > in userspace. This should even work for block filesystems on top
> > > of UBI
> > > as root fs as you can remount them later RW.
> > > 
> > > Sounds like a plan?
> > I would see something a little bit better (from a user
> > perspective), though
> > I don't know if it's possible. It would be nice to mark the UBI
> > image RO/RW
> > when it is created via ubiformat. That would be a bit stored on the
> > ubiblock
> > itself. That way the decision is taken at creation time and is not
> > changed
> > later (or only using a specific tool). Note that it is very
> > possible I'm
> > missing something important, but you get the idea.
> ubiblock is just a layer above an UBI volumes.
> We could add a new UBI volume flag for RW ubiblock.

You can add a per-volume R/O flag if needed, yes. Expose it to user-
space. This may be a useful thing irrespectively. I am not sure how it
helps with ubiblock though.

Ideally, the ubiblock R/W enabled flag should be stored in ubiblock,
not in UBI, not in MTD, because you want ubiblock to have full control
over it. You do not want a user go and change the flag via the UBI
interface whenever the user feels like, right?

To have this kind of flag in ubiblock, it needs an on-flash superblock
or something. If you are not going to introduce it, which I believe is
the case, then the only option left in my opinion is a ubiblock module
parameter.

If I am a ubiblock user who needs the write support, and this naive
write support is good enough for me, I want it enabled by default on my
product. A module parameter with a sound name like 'dangerous-write-
support' or something would work fine for me.

Artem.