On 12/06/2018 01:33 PM, Dongsheng Yang wrote:
On 12/06/2018 12:16 AM, Jason Dillaman wrote:
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).
+1 for this.
Can we introduce a new service to watch all images mapped on a node?
If we start a new process for each rbd map, that's a little expensive. we
can start a single service to watch all of them, register in rbd map and
unregister in rbd unmap.
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
