On 3/6/23 20:18, Miklos Szeredi wrote: > On Mon, 6 Mar 2023 at 17:44, Aleksandr Mikhalitsyn > <aleksandr.mikhalitsyn@xxxxxxxxxxxxx> wrote: >> >> On Mon, Mar 6, 2023 at 5:15 PM Miklos Szeredi <miklos@xxxxxxxxxx> wrote: > >>> Apparently all of the added mechanisms (REINIT, BM_REVAL, conn_gen) >>> are crash recovery related, and not useful for C/R. Why is this being >>> advertised as a precursor for CRIU support? >> >> It's because I'm doing this with CRIU in mind too, I think it's a good >> way to make a universal interface >> which can address not only the recovery case but also the C/R, cause >> in some sense it's a close problem. > > That's what I'm wondering about... > > Crash recovery is about restoring (or at least regenerating) state in > the userspace server. > > In CRIU restoring the state of the userspace server is a solved > problem, the issue is restoring state in the kernel part of fuse. In > a sense it's the exact opposite problem that crash recovery is doing. > >> But of course, Checkpoint/Restore is a way more trickier. But before >> doing all the work with CRIU PoC, >> I wanted to consult with you and folks if there are any serious >> objections to this interface/feature or, conversely, >> if there is someone else who is interested in it. >> >> Now about interfaces REINIT, BM_REVAL. >> >> I think it will be useful for CRIU case, but probably I need to extend >> it a little bit, as I mentioned earlier in the cover letter: >>>> * "fake" daemon has to reply to FUSE_INIT request from the kernel and initialize fuse connection somehow. >>>> This setup can be not consistent with the original daemon (protocol version, daemon capabilities/settings >>>> like no_open, no_flush, readahead, and so on). >> >> So, after the "fake" demon has done its job during CRIU restore, we >> need to replace it with the actual demon from >> the dumpee tree and performing REINIT looks like a sanner way. > > I don't get it. How does REINIT help with switching to the real daemon? The way I read the patches, the new daemon sends FUSE_INIT to advertise all of its features.
