ubifs+overlayfs

[Vivek Goyal]

On Mon, Feb 22, 2016 at 08:19:21AM +1100, Dave Chinner wrote:
> On Sun, Feb 21, 2016 at 03:27:18PM +0100, Richard Weinberger wrote:
> > Cc'ing linux-mtd.
> > 
> > On Sat, Feb 20, 2016 at 1:02 AM, Pushpal Sidhu <psidhu at gateworks.com> wrote:
> > > It seems that overlayfs requires RENAME_WHITEOUT and RENAME_EXCHANGE.
> > > However, these two flags aren't currently supported in ubifs (or
> > > anything other than ext4, f2fs, and xfs). This causes any atomic
> > > renames to fail (e.g. using 'mv' command).
> > 
> > Hmm, right. I always thought overlayfs does checks at mount time.
> > But apparently I was wrong.
> > Thanks for pointing this out.
> 
> It doesn't check any of the requirements it has from the underlying
> filesystem. e.g. overlay requires DT_CHR for detecting whiteouts,
> but it doesn't check if the upper filesystem actually supports
> DT_CHR or not, and hence will fail to detect whiteouts correctly on
> such filesystems. I've been pushing people to fix this, so maybe
> patches will appear in the not too distant future...

Dave pushed me to write the patch to detect whether upper filesystem
supports d_type or not :-). I will cleanup what I have and post for
review.

Thanks
Vivek