On Mon, Jul 31, 2017, at 12:32 PM, Colin Walters wrote: > On Mon, Jul 31, 2017, at 12:29 PM, Dan Williams wrote: > > > > How is S_CONTENTS_IMMUTABLE different than S_IMMUTABLE? > > We still want the ability to make hardlinks.
Also of course, symmetrically, to unlink. If we used S_IMMUTABLE for /etc/sudoers, it'd still be racy since one would have to transiently remove the flag in order to replace it with a new version. Related to this topic is the fact that S_IMMUTABLE is itself mutable; I think once S_IMMUTABLE_CONTENTS is set, it would not be able to made mutable again. Also I just remembered that since then memfd_create() and more notably fcntl(F_ADD_SEALS) landed - in fact it already has flags for what we want here AFAICS. Your S_IOMAP_IMMUTABLE is fcntl(F_ADD_SEALS, F_SEAL_SHRINK | F_SEAL_GROW) and mine just adds in F_SEAL_WRITE. I think there was some discussion of the seals for persistent files when memfd_create() landed, but I can't find it offhand.
