[sheepdog] [PATCH v2 3/3] sheep: remove cache object for discard operation

[Hitoshi Mitake]

At Mon, 15 Jul 2013 14:28:48 +0800,
Liu Yuan wrote:
> 
> Signed-off-by: Liu Yuan <namei.unix at gmail.com>
> ---
>  sheep/object_cache.c |   28 ++++++++++++++++++++++++++++
>  sheep/sheep_priv.h   |    1 +
>  sheep/store.c        |    6 ++++++
>  3 files changed, 35 insertions(+)
> 
> diff --git a/sheep/object_cache.c b/sheep/object_cache.c
> index e3270df..1579a30 100644
> --- a/sheep/object_cache.c
> +++ b/sheep/object_cache.c
> @@ -1317,6 +1317,34 @@ out:
>  	return ret;
>  }
>  
> +int object_cache_remove(uint64_t oid)
> +{
> +	/* Inc the entry refcount to exclude the reclaimer */
> +	struct object_cache_entry *entry = oid_to_entry(oid);
> +	struct object_cache *oc = entry->oc;
> +	int ret;
> +
> +	if (!entry)
> +		return SD_RES_NO_OBJ;
> +
> +	sd_dprintf("%" PRIx64, oid);
> +	while (refcount_read(&entry->refcnt) > 1)
> +		usleep(100000); /* Object might be in push */

I believe this sort of magic number based coding should be
avoided.

coroutine would be suitable for writing this type of code cleanly. How
about recover it? I've heard that the previous sheepdog had coroutine
but it was reverted because of poor compatibility with valgrind.

But I believe coroutine is worth considering to use, because other
code in sheepdog (e.g. swithc_journal_file()) would be able to enjoy
it.

Thanks,
Hitoshi