[Sheepdog] [PATCH] sheep: add an option to disable object cache

[Christoph Hellwig]

On Thu, May 10, 2012 at 03:46:55AM +0900, MORITA Kazutaka wrote:
> It is highly recommended to read the document carefully before using
> the object cache.
> 
>   https://github.com/collie/sheepdog/wiki/Backend-Stores-and-Object-Cache
> 
> This patch is useful for users who cannot accept the limitation
> (e.g. sheep requires additional store on the gateway nodes,
> writethrough and writeback cannot be mixed to the same image, etc).
> If you are unsure how the object cache works, it's safe to disable it.
> 
> In future, it's better to support multiple cache features because the
> requirements for the sheepdog write cache seem to be quite different
> among users.

The code looks fine, although I'd still vote for default to off.

I also wonder if there's a better way to hide the check inside the
actual object_ routines, but I'd need to look at it in more detail to
figure out how.