[Sheepdog] [PATCH v2 2/3] sheep: timestamp the epoch log

[MORITA Kazutaka]

At Wed, 26 Oct 2011 15:26:51 +0800,
Liu Yuan wrote:
> 
> On 10/26/2011 03:12 PM, MORITA Kazutaka wrote:
> 
> >>> @@ -147,6 +147,7 @@ struct sheepdog_vnode_list_entry {
> >>>  
> >>>  struct epoch_log {
> >>>  	uint64_t ctime;
> >>> +	time_t time;
> >>>  	uint32_t epoch;
> >>>  	uint32_t nr_nodes;
> >>>  	struct sheepdog_node_list_entry nodes[SD_MAX_NODES];
> > 
> > This is not 64 bit aligned.
> > 
> 
> 
> What do you mean by alignment? So where you suggest to place time in
> this structure?

For all structures which can be shared between the different
architecture, we should use architecture-independent types
(e.g. uint64_t) and align them to 64 bits.  For example, if you have
64 bit machines for Sheepdog cluster and run 'collie cluster info' on
the 32 bit machine, it will fail.

Actually, sizeof(struct epoch_log) is 24600 bytes on my 64 bit Linux
machine, and 24596 bytes on 32 bit machine.

> 
> > 
> >>> diff --git a/sheep/ops.c b/sheep/ops.c
> >>> index 743eb0f..e2d7fb1 100644
> >>> --- a/sheep/ops.c
> >>> +++ b/sheep/ops.c
> >>> @@ -279,6 +279,7 @@ static int local_stat_cluster(const struct sd_req *req, struct sd_rsp *rsp,
> >>>  
> >>>  		rsp->data_length += sizeof(*log);
> >>>  		log->nr_nodes /= sizeof(log->nodes[0]);
> >>> +		log->time = *(time_t *)(&log->nodes[log->nr_nodes]);
> > 
> > Looks a bit hacky to me.  In addition, this doesn't work if
> > sizeof(log->nodes[0]) < sizeof(time_t).
> 
> 
> 
> Yes, tricky, but simplest. even sizeof(log->nodes[0]) < sizeof(time_t), I think this works out, cause
> 
> we just need to get the address of end of the nodes array. Dereference
> is okay since it has converted into the right type(time_t *).

If sizeof(log->nodes[0]) < sizeof(time_t),
log->nr_nodes /= sizeof(log->nodes[0]) doesn't set the correct number
of nodes.

> 
> any other more suitable means?

I think we should define the epoch log layout and include followings:

 - the number of nodes
 - the array of node
 - timestamp


Thanks,

Kazutaka

> 
> Thanks,
> Yuan
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