> O.k., I see the point. But: why does unionfs lookup a whiteout in a read-only 
> branch?

While I was thinking about Wilhelm's question, I've got an idea of new
option "dirs=<branch>=ro_wh".
Currently these options are 'ro' and 'rw'. A 'ro_wh' option is
perfectly equivalent to current 'ro'. But the meaning of 'ro' option
changes. In case of 'ro', unionfs does not lookup a whiteout entry, but
'ro_wh' does.
Reducing the number of lookup will get a chance to make unionfs
lighter. I hope it will be effective to the simple cases, like tmpfs +
large cd/dvd image, tmpfs + readonly nfs, tmpfs + regular mntpnt and so
on. These cases will not need to modify the unionfs option. And I guess
that most users would use unionfs like this.
But it may not be effective in the complex cases, like the
branch is specified readonly currently but it had been writable, or it
is a writable branch of another unionfs. In these cases, user will need
to change the option from 'ro' to 'ro_wh', to keep on looking-up on the
readonly branch.

I have once thought it doesn't need to lookup on the lowest branch only.
But now I think most readonly branch does not need to lookup whiteout,
and it is better to introduce a new option and make it choosable by
user.

How do you think about changing the meaning of 'ro'? > all of users and
developers
If I write a patch, will it be merged?


Junjiro Okajima
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