[Ocfs2-devel] [PATCH 00/11] ocfs2: implement userspace clustering interface

[Jeff Mahoney]

Hello all -

As mentioned in my last email, here are my patches for implementing a userspace
clustering interface.

These should be considered early beta, but I very much welcome comment.

A quick preview:
01 - event driven quorum: o2net will no longer call into quorum
     directly, but rather generate events that quorum will hook into.
     Unfortunately, I've run into a bit of a snag with this since there
     are two places where recursive events can be generated (ie: a
     connection event generated when handling a node up/down event) and
     that causes deadlocks on the o2hb_callback_sem. This is really
     the only patch the entire series is waiting on sorting out.
02 - introduce generic heartbeat resource: initially, this will
     just contain a config_item and will replace the config_item
     in o2hb_region. Eventually, it will be used as a handle for a
     generic heartbeat resource, including several operations.
03 - split disk heartbeat out from the generic heartbeat: They'll still
     be closely tied, but going their separate ways. This patch
     intentionally does very little other than move code around without
     modifying it.
04 - add a heartbeat registration API: This expands the generic
     heartbeat group structure to include the type information as well
     as a few operations necessary to abstract the heartbeat resource.
     In addition, it adds a mechanism for registering a group mode. It
     uses the first mode loaded. Since disk is the only mode at this
     point, there is no way to switch. This will be added later.
05 - add per-resource events: callbacks can define that they only want
     events from a particular heartbeat resource, and will only receive
     events for those. This is useful for only sending the file system
     the events from the heartbeat resource it's listening to.
06 - per-resource membership: fill_node_map can take a resource name
     (UUID) to use for filling the membership bitmap passed in. If NULL
     is passed, it uses a global up/down. No changes to the disk
     heartbeat other than prototype changes are needed, since it still
     keeps a global membership.
07 - o2net refcounted disconnect: Rather than disconnect when a node
     down event is caught by o2net, it waits until the last reference
     is dropped. This is useful for userspace heartbeat since it can
     take down a disk resource but the network resource will still be
     available.
08 - add check_node_status: The userspace heartbeat implementation
     allows the caller to check on a per-node, per-resource basis if
     a particular node is up. Building the global list is a bigger deal,
     so when that is avoidable, it does so.
09 - add /sys/o2cb/heartbeat_mode: This patch allows the user to select
     which mode heartbeat will use. It requires that the change be made
     before the cluster is created.
10 - add userspace clustering: The real goal of all this. This will
     allow the user to create heartbeat directories as before, but
     rather than supplying disk information, it allows the user to
     create symlinks to communicate the current node membership for
     a given heartbeat group. Since configfs doesn't allow dangling
     symlinks, this is an easy way to intuitively configure heartbeat
     resources from userspace. Node UP events are generated when a link
     is created and node DOWN events are generated when a link is
     removed.

-Jeff

--
Jeff Mahoney
SUSE Labs