[Sheepdog] [PATCH] object cache: add flush_and_delete operation

[MORITA Kazutaka]

At Tue,  3 Apr 2012 16:03:57 +0800,
Liu Yuan wrote:
> 
> From: Liu Yuan <tailai.ly at taobao.com>
> 
> If 1) VDI is opened without cache enabled and 2) we unfortunately have
> a cache for it previously, we should flush the cache then delete it.
> 
> Signed-off-by: Liu Yuan <tailai.ly at taobao.com>
> ---
>  sheep/object_cache.c |   42 ++++++++++++++++++++++++++++++++++++++++++
>  sheep/sheep_priv.h   |    1 +
>  sheep/store.c        |   30 +++++++++++++++++++++---------
>  3 files changed, 64 insertions(+), 9 deletions(-)
> 
> diff --git a/sheep/object_cache.c b/sheep/object_cache.c
> index b59f8f7..e856be4 100644
> --- a/sheep/object_cache.c
> +++ b/sheep/object_cache.c
> @@ -20,6 +20,7 @@
>  #include <pthread.h>
>  #include <errno.h>
>  #include <sys/file.h>
> +#include <dirent.h>
>  
>  #include "sheep_priv.h"
>  #include "util.h"
> @@ -526,6 +527,47 @@ void object_cache_delete(uint32_t vid)
>  
>  }
>  
> +int object_cache_flush_and_delete(struct object_cache *oc)
> +{
> +	DIR *dir;
> +	struct dirent *d;
> +	uint32_t vid = oc->vid;
> +	uint32_t idx;
> +	struct strbuf p;
> +	int ret = 0;
> +
> +	strbuf_init(&p, PATH_MAX);
> +	strbuf_addstr(&p, cache_dir);
> +	strbuf_addf(&p, "/%06"PRIx32, vid);
> +
> +	dprintf("%"PRIx32"\n", vid);
> +	dir = opendir(p.buf);
> +	if (!dir) {
> +		dprintf("%m\n");
> +		ret = -1;
> +		goto out;
> +	}
> +
> +	while ((d = readdir(dir))) {
> +		if (!strncmp(d->d_name, ".", 1))
> +			continue;
> +		idx = strtoul(d->d_name, NULL, 16);
> +		if (idx == ULLONG_MAX)
> +			continue;
> +		if (push_cache_object(vid, idx, 1) != SD_RES_SUCCESS) {
> +			dprintf("failed to push %"PRIx64"\n",
> +				idx_to_oid(vid, idx));
> +			ret = -1;
> +			goto out;
> +		}
> +	}
> +
> +	object_cache_delete(vid);
> +out:
> +	strbuf_release(&p);
> +	return ret;
> +}
> +
>  int object_cache_init(const char *p)
>  {
>  	int ret = 0;
> diff --git a/sheep/sheep_priv.h b/sheep/sheep_priv.h
> index d687cc0..c01ee46 100644
> --- a/sheep/sheep_priv.h
> +++ b/sheep/sheep_priv.h
> @@ -429,5 +429,6 @@ int object_cache_push(struct object_cache *oc);
>  int object_cache_init(const char *p);
>  int object_is_cached(uint64_t oid);
>  void object_cache_delete(uint32_t vid);
> +int object_cache_flush_and_delete(struct object_cache *oc);
>  
>  #endif
> diff --git a/sheep/store.c b/sheep/store.c
> index 6661f13..84bffc2 100644
> --- a/sheep/store.c
> +++ b/sheep/store.c
> @@ -835,16 +835,28 @@ static int bypass_object_cache(struct sd_obj_req *hdr)
>  {
>  	uint64_t oid = hdr->oid;
>  
> -	/*
> -	 * We assume the cached object is freshest, donot break it ever.
> -	 * This assumption is useful for non-cache requests from collie,
> -	 * which tries hard to get the newest data.
> -	 */
> -	if (object_is_cached(oid))
> -		return 0;
> +	if (!(hdr->flags & SD_FLAG_CMD_CACHE)) {
> +		uint32_t vid = oid_to_vid(oid);
> +		struct object_cache *cache;
>  
> -	if (!(hdr->flags & SD_FLAG_CMD_CACHE))
> -		return 1;
> +		cache = find_object_cache(vid, 0);
> +		if (!cache)
> +			return 1;
> +		if (hdr->flags & SD_FLAG_CMD_WRITE) {
> +			object_cache_flush_and_delete(cache);

Hmm, does this work well when multiple write requests arrive at the
same time?  I cannot come up with a better approach, though.

BTW, do we really need to split a object cache into 4 MB files?  It
looks simpler and faster to use a single large and sparse file for the
object caches (the file has the same size and content with the virtual
disk) since we can avoid extra open/close calls.

Thanks,

Kazutaka