On Wed, Sep 23, 2020 at 10:47 PM Vivek Goyal <vgoyal@xxxxxxxxxx> wrote: > > On Wed, Sep 23, 2020 at 06:23:08PM +0300, Pavel Tikhomirov wrote: > > This relaxes uuid checks for overlay index feature. It is only possible > > in case there is only one filesystem for all the work/upper/lower > > directories and bare file handles from this backing filesystem are uniq. > > Hi Pavel, > > Wondering why upper/work has to be on same filesystem as lower for this to > work? > I reckon that's because I asked for this constraint, so I will answer. You are right that the important thing is that all lower layers are on the same fs, but because of a888db310195 ovl: fix regression with re-formatted lower squashfs I preferred to keep the rules simpler. Pavel's use case is clone of disk and change of its UUID. This is a real use case and I don't think it is unique to Virtuozzo, so I wanted index=nouuid to address that use case only and I prefer that it is documented that way too. Ironically, one of the justifications for index=nouuid is virtiofs - because fuse is now allowed as upper (or as same fs), one can already use fuse passthough (or one could use fuse passthrough when nfs export works correctly) as a "uuid anonymizer" for any fs, so in practice, index=nouuid cannot do any more harm then one can already do when enabling index over virtiofs. That is why I prefer the interpretation that index=nouuid means "use null uuid instead of s_uuid for ovl_fh" over the interpretation "relax comparison of uuid in ovl_fh". Thanks, Amir.
