On Tue, Oct 25, 2016 at 2:24 PM, Amir Goldstein <amir73il@xxxxxxxxx> wrote: > On Tue, Oct 25, 2016 at 10:34 AM, Miklos Szeredi <mszeredi@xxxxxxxxxx> wrote: >> To allow adding new, backward incompatible features to overlayfs, we need a >> way to store the list of features in the overlay. This is done via >> "trusted.overlay.features" xattr on the root of the upper layer (or one of >> the lower layers, that previously acted as an upper layer). It's a comma >> separated list of case sensitive strings. >> >> If an overlay has an unknown feature, mount shall return an error. So >> mechanism should only be used for backward incompatible features. > > So maybe be explicit and call the attribute trusted.overlay.incompat_features, > to allow future addition of compat and rocompat feature sets? > On top of the proposed features xattr, for the sake of being backward compatible with old kernels, how about creating a file 3 levels down from work dir (e.g. /work/work/a/b/c) This would cause old kernels to mount overlay read-only, which is sufficient to keep them from corrupting the redirect structure. And once again, I suggest learning from the elders fs, who have successfully gone through many on-disk format upgrades, and copy the design of the feature trio (compat/incompat/rocompat) Amir. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
