[sheepdog] [PATCH 1/4] sheep: fix typo in help information

[MORITA Kazutaka]

At Mon, 25 Nov 2013 15:03:46 +0800,
Robin Dong wrote:
> 
> The present implementation of http/swift is not perfect, it can't create
> too much containers or objects. So we want to store all objects in one
> hyper volume vdi and use new structure 'obj-inode' to identify its offset
> and length in this vdi, just like some local file system. To achieve this,
> we need distributed locks to ensure that only one thread can create a new
> 'obj-inode' (or delete) in this vdi at a same time.
> 
> This patch set is a try to implement the distributed lock.
> 
> If we add code in sheep/cluster/zookeeper.c and use the framework of
> cluster to implement this distributed lock, then we have to add
> implementation for corosync、local and shepherd. That's too complicated. So
> what we need is adding lock.c in sheep/http/ and only use it in http
> interface.

If possible, I don't like to see zookeeper specific codes out side of
sheep/cluster/zookeeper.c.  Can we use a SD_OP_TYPE_CLUSTER operation
for your purpose?  It works like a cluster-wide distributed lock.

For example, vdi creation works like as follows.

 1. When sheep receives a SD_OP_NEW_VDI operation, sheep calls
    cdrv->block() to block all the other cluster operations.

 2. Sheep calls cluster_new_vdi() in sd_block_handler().  It is
    ensured that no other sheep call sd_block_handler() at the same
    time.  This is necessary here because sheepdog doesn't allow
    concurrent vdi creation requests.

 3. All the sheep in the cluster call post_cluster_new_vdi() in
    sd_notify_handler().  It is usually used for notification or
    cleanups.

Thanks,

Kazutaka