[Sheepdog] [PATCH] sheep: fix read_copy_from_cluster()

[Liu Yuan]

On 04/13/2012 11:40 PM, Christoph Hellwig wrote:

> On Fri, Apr 13, 2012 at 09:54:14PM +0800, Liu Yuan wrote:
>> From: Liu Yuan <tailai.ly at taobao.com>
>>
>> We should pass nr_vnodes to the obj_to_sheep()
> 
> Seems like it should to prevent problems if not enough zones are
> availably during recovery.  Is that true?  A slightly more detailed
> explanation of patches would be really useful, as would test cases
> (even if the latter might be a bit harder to produce).
> 


Yes, but not only in recovery process, there is case that number of
available nodes or zones is less than 'copies', where we shouldn't pass
non-existent copy index to obj_to_sheep().

This is a apparent bug that pass the wrong parameter to the
obj_to_sheep() for second argument. That is, we should pass number of
vnodes instead of nr of copies.

Anyway, I think obj_to_sheep(), which calculate the object location from
the hash ring, need to be refined:
1) it would better handle the case 'nodes(zones) < copies' internally,
not demand the caller to do it. Because if caller doesn't do it, it will
result in panic when it happens.
2) get a better name, such as int object_to_ring_index(oid, vnodes,
nr_vnodes, copy_idx).

Thanks,
Yuan