On Wed, Nov 01, 2017 at 06:41:51PM +0200, Amir Goldstein wrote: [..] > >> I can't remember if there was a reason for not allocating anonymous bdev > >> for upper > > > > That's a good point. > > > >> or if it just because we did not need it to guaranty uniqueness > >> of st_dev/st_ino *among* overlay inodes > > > > Even for lower, st_dev will be unique for different lower on non same-fs, > > right. IOW, when it come to uniqueness of st_dev/st_ino pair, among > > overlay inodes, lower and upper should have same requirements. > > > >> while guarantying constant > >> st_dev/st_ino across copy up. > > > > Hmm..., I did not get this point. Over copy up, atleast st_ino will change > > for non-samefs case. > > > > I will spend more time on patch. > > > > Urgh! It took me a while to remember the reason why system wide uniqueness > is important for lower but less for upper. > An upper object has the same content as the "real" object and they have the > same st_ino/st_dev so its ok that diff will skip comparing them. > A copy-up object does not have the same content as the lower "real" object, > so if it has the same st_ino/st_dev as real object, diff will skip compare and > we have a problem. I am not sure I understand this. So you are doing a diff between a file on overlayfs and same file accessed outside overlayfs? If a file is on lower, then it has not been modified and diff skipping it makes perfect sense? Vivek -- To unsubscribe from this list: send the line "unsubscribe linux-unionfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
