On Mon, 2017-06-12 at 01:06 +0800, Zhu Lingshan wrote: > I am working on PR support for RBD in user space, aka, give tcmu-runner > rbd handler ability to handle Persistent Reservation operations. Now RBD > handler side works fine, I can capture the CDBs, analyze it, store/ read > keys, also other supportive codes done and works fine. Hello Zhu, Since handling PR in user space would add significant complexity (due to the new interfaces between kernel and user space that are required) and also has significant disadvantages (Mike Christie mentioned the overhead due to the reservation state check), can you explain why you think it would be useful to handle PR commands in user space instead of keeping all PR command processing in the kernel? If you are looking at this to support synchronizing the PR state across multiple nodes in a cluster I think handling PR in user space is wrong because that means the solution to synchronize the PR state across nodes will be limited to RBD and won't work for clusters that don't use RBD. Are you aware that reliable open source code exists for synchronizing the PR state across multiple cluster nodes? See also https://www.linuxplumbersconf.org/2015/ocw/system/presentations/2691/original/Using%20the%20DLM%20as%20a%20Distributed%20In-Memory%20Database.pdf Bart.-- To unsubscribe from this list: send the line "unsubscribe target-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
