On Tue, Nov 17, 2020 at 06:19:56PM -0500, Joel Fernandes (Google) wrote: > From: Josh Don <[email protected]> > > Google has a usecase where the first level tag to tag a CGroup is not > sufficient. So, a patch is carried for years where a second tag is added which > is writeable by unprivileged users. > > Google uses DAC controls to make the 'tag' possible to set only by root while > the second-level 'color' can be changed by anyone. The actual names that > Google uses is different, but the concept is the same. > > The hierarchy looks like: > > Root group > / \ > A B (These are created by the root daemon - borglet). > / \ \ > C D E (These are created by AppEngine within the container). > > The reason why Google has two parts is that AppEngine wants to allow a subset > of > subcgroups within a parent tagged cgroup sharing execution. Think of these > subcgroups belong to the same customer or project. Because these subcgroups > are > created by AppEngine, they are not tracked by borglet (the root daemon), > therefore borglet won't have a chance to set a color for them. That's where > 'color' file comes from. Color could be set by AppEngine, and once set, the > normal tasks within the subcgroup would not be able to overwrite it. This is > enforced by promoting the permission of the color file in cgroupfs.
Why can't the above work by setting 'tag' (that's a terrible name, why does that still live) in CDE? Have the most specific tag live. Same with that thread stuff. All this API stuff here is a complete and utter trainwreck. Please just delete the patches and start over. Hint: if you use stop_machine(), you're doing it wrong. At best you now have the requirements sorted.
