On Wed, Dec 5, 2018 at 5:17 AM Ilya Dryomov <idryomov@xxxxxxxxx> wrote: > > On Wed, Dec 5, 2018 at 3:46 AM Dongsheng Yang > <dongsheng.yang@xxxxxxxxxxxx> wrote: > > > > Hi Ilya and Jason, > > Maybe there is another option, umh (user mod helper): > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/umh.h > > We can provide a subcommand in userspace for journal replaying, and we > > can check the journal in rbd map and reaquire exclusive-lock, if we > > find there is uncommitted entry, we can call userspace helper by umh to > > replay it. > > Yes, making an upcall from the kernel might be an option, but the > problem is that this can happen deep in the I/O path. I'm not sure > it's safe wrt memory allocation deadlocks because the helper is ran > out of a regular workqueue, etc. > > Another option might be to daemonize "rbd map" process. > > Or maybe attempting a minimal replay in the kernel and going read-only > in case something is wrong is actually fine as a starting point... I'd vote for daemonizing "rbd map" (or a similar small, purpose-built tool). The local "rbd-mirror" daemon process doesn't currently open a watch on local primary images and in the case of one-way mirroring, you would potentially not even have an "rbd-mirror" daemon running locally. > Thanks, > > Ilya -- Jason
