ubifs+overlayfs

[Dave Chinner]

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...

Cheers,

Dave.
-- 
Dave Chinner
david at fromorbit.com