At Thu, 20 Dec 2012 02:29:31 +0800,
Liu Yuan wrote:
>
> From: Liu Yuan <tailai...@taobao.com>
>
> Sheepdog supports both writeback/writethrough write but has not yet supported
> DIRECTIO semantics which bypass the cache completely even if Sheepdog daemon
> is
> set up with cache enabled.
>
> Suppose cache is enabled on Sheepdog daemon size, the new cache control is
>
> cache=writeback # enable the writeback semantics for write
> cache=writethrough # enable the writethrough semantics for write
> cache='directsync | none | off' # disable cache competely
I wonder if we should disable cache when cache=none. Many management
frontend uses cache=none by default but, I think, users still expect
that data is cached (e.g. by disk write cache when a raw format is
used). cache=none only means that the host page cache is not used for
VM disk IO.
In that sense,
> @@ -1118,12 +1118,19 @@ static int sd_open(BlockDriverState *bs, const char
> *filename, int flags)
> goto out;
> }
>
> - s->cache_enabled = true;
> - s->flush_fd = connect_to_sdog(s->addr, s->port);
> - if (s->flush_fd < 0) {
> - error_report("failed to connect");
> - ret = s->flush_fd;
> - goto out;
> + if (flags & BDRV_O_NOCACHE) {
> + s->cache_flags = SD_FLAG_CMD_DIRECT;
> + } else if (flags & BDRV_O_CACHE_WB) {
'else' should be removed, and
> + s->cache_flags = SD_FLAG_CMD_CACHE;
> + }
> +
> + if (s->cache_flags != SD_FLAG_CMD_DIRECT) {
should be 's->cache_flags == SD_FLAG_CMD_CACHE'? Do we need to send a
flush request when cache=writethourgh?
Thanks,
Kazutaka
