On Mon, May 02, 2022 at 05:40:02PM +0200, Lennart Poettering wrote: > On Mo, 02.05.22 16:06, Jason A. Donenfeld (Jason@xxxxxxxxx) wrote: > > > In order to inform userspace of virtual machine forks, this commit adds > > a "fork_event" sysctl, which does not return any data, but allows > > userspace processes to poll() on it for notification of VM forks. > > > > It avoids exposing the actual vmgenid from the hypervisor to userspace, > > in case there is any randomness value in keeping it secret. Rather, > > userspace is expected to simply use getrandom() if it wants a fresh > > value. > > Wouldn't it make sense to expose a monotonic 64bit counter of detected > VM forks since boot through read()? It might be interesting to know > for userspace how many forks it missed the fork events for. Moreover it > might be interesting to userspace to know if any fork happened so far > *at* *all*, by checking if the counter is non-zero. "Might be interesting" is different from "definitely useful". I'm not going to add this without a clear use case. This feature is pretty narrowly scoped in its objectives right now, and I intend to keep it that way if possible. (And yes, I realize that is likely considerably different from your development philosophy.) > > (Ideally that counter file would even be mmapable...) You missed the last year of discussion about this and why we have wound up here as a first step. Check the archives for extensive discussion. Jason
