[sheepdog] [PATCH 1/3] sheep: use qemu cache option to use writeback/writethrough mode

[Liu Yuan]

On 08/30/2012 05:02 PM, MORITA Kazutaka wrote:
> When writeback is enabled, SD_FLAG_CMD_CACHE flag is set to I/O
> requests.  This patch uses it for write mode.
> 
> Signed-off-by: MORITA Kazutaka <morita.kazutaka at lab.ntt.co.jp>
> ---
>  sheep/object_cache.c |   83 ++++++++++++-------------------------------------
>  sheep/request.c      |    2 +-
>  sheep/sheep.c        |   13 +------
>  sheep/sheep_priv.h   |    1 -
>  4 files changed, 24 insertions(+), 75 deletions(-)
> 
> diff --git a/sheep/object_cache.c b/sheep/object_cache.c
> index a722259..431fe26 100644
> --- a/sheep/object_cache.c
> +++ b/sheep/object_cache.c
> @@ -75,9 +75,6 @@ struct object_cache {
>  	struct rb_root object_tree;
>  
>  	pthread_rwlock_t lock;
> -
> -	int (*read)(struct object_cache_entry *, void *, size_t, off_t);
> -	int (*write)(struct object_cache_entry *, void *, size_t, off_t, int);
>  };

So object cache was enabled unconditionally? I guess this will cause trouble for people
don't want to enable any cache at sheepdog side at all. (object cache will take up local disk
space)

I am considering to change the qemu flag semantics for cache control:

 BDRV_O_NOCACHE (cache=off or none, directsync) --> no cache at all
 BDRV_O_CACHE_WB (cache=writeback) --> use writeback cache (Leave user to decide object cache
or other writeback cache in sheepdog)
 no NOCACHE or CACHE_WB flag (default as writetrhough) --> use writethrough cache (even for writethrough
cache, I think user should have an option to set cache size for cache reclaim)

Besides, user can have option to disable cache on sheepdog.

Thanks,
Yuan