Re: [RFC PATCH] Show data flow for file copyup in unions

[Valerie Aurora <vaurora@redhat.com>]

On Thu, Mar 18, 2010 at 05:10:57PM +0900, J. R. Okajima wrote:
> 
> Valerie Aurora:
> > I think what people will expect is that we copy up in that case.  I
> > can think of ways this can go wrong, but perhaps that should be an
> > explicit requirement on the top-layer file system, that it can handle
> > create/unlink() in a directory without write permission.
> 
> I am not sure such requirement is the right way.
> How about delegating open() to keventd or some other workqueue which
> will succeed to create files under a directory without write permission?
> Of course, we should handle some error cases after creating a file.

Hm, I don't understand how handing it off to another thread would
help.  The thing I am worried about is some internal assumption in the
file system that a directory without write permission can't be
changed.  Totally manufactured example:

somefs_create()
{
	BUG_ON(IS_RDONLY(dir->d_inode);
[...]
}

-VAL