UBI_READWRITE constraint when opening volumes to rename

[Artem Bityutskiy]

On Mon, 2014-10-20 at 13:10 +0200, Richard Weinberger wrote:
> This is why I need to review all code paths first.
> My initial patch was not supposed to be a final solution, more a base for discussion.
> I.e. to follow the "less talk, more code" rule.

Let me try to summarise.

Exclusive mode - used for volume and LEB update. We do not want someone
to race with these operations on the same LEBs. Indeed, if one performs
a volume or LEB update, we want to guarantee that that the result of the
operation is that the volume/LEB contains the data user sent us.

Read/write - just R/W mode, many users may race

Read-only - when we know we should not write to the volume, and want UBI
to refuse our writes in case we try to write, say, because of a bug in
UBIFS code.

AFAICS, all the modes are useful.

Metaonly - we are not going to change the data, only the meta-data like
the volume name. Seem to be a good idea to me, thanks!