On Wed, Apr 26, 2017 at 5:02 PM, Amir Goldstein <amir73il@xxxxxxxxx> wrote: > On Wed, Apr 26, 2017 at 5:53 PM, Miklos Szeredi <miklos@xxxxxxxxxx> wrote: >> On Wed, Apr 26, 2017 at 4:40 PM, Miklos Szeredi <miklos@xxxxxxxxxx> wrote: >> >>> The reason I think the COPYUP vs. MERGE distinction is needed is the >>> ovl_check_empty_and_clear() thing. It starts with a merged directory >>> with some whiteouts in it and exchanges it with an empty and opaque >>> directory. Normally the empty directory will be deleted immediately, >>> but if something fails during the deletion, then it will remain there. >>> The overlay is left in a consistent state, but the association with >>> the original inode should still remain, so it will have COPYUP but not >>> MERGE. >> >> One more thought: we could introduce a separate "overlay.merge" >> attribute that is the exact opposite of "overlay.opaque". >> "overlay.merge" would imply "overlay.fh" but "overlay.fh" would not >> imply "overlay.merge". >> >> It would allow us to optionally get rid of "overlay.opaque" when back >> compatibility is not needed. >> >> It would also allow a new feature: on metadata only updates of regular >> files we wouldn't need to copy up the data. >> > > So you intend to set overlay.merge for non-dir? Nope, not by default. > How is it different from overlay.fh then? It would make sense for regular files for the non-samefs or non-clone fs cases if only metadata (attr, xattr) are modified but data is not. We'd create an empty file with the copied up metadata and "overlay.merge" set indicating that the data I/O should still be redirected to the origin, while metadata is kept in the copied up file. This can be upgraded to a fully copied-up file later. Not something for this series, obviously. Thanks, Miklos
