Re: [Qemu-devel] [PATCH] rbd: hook up cache options

[Paolo Bonzini]

Il 17/05/2012 22:42, Josh Durgin ha scritto:
> +     * Fallback to more conservative semantics if setting cache
> +     * options fails. Ignore errors from setting rbd_cache because the
> +     * only possible error is that the option does not exist, and
> +     * librbd defaults to no caching. If write through caching cannot
> +     * be set up, fall back to no caching.
> +     */
> +    if (flags & BDRV_O_NOCACHE) {
> +        rados_conf_set(s->cluster, "rbd_cache", "false");
> +    } else {
> +        rados_conf_set(s->cluster, "rbd_cache", "true");
> +        if (!(flags & BDRV_O_CACHE_WB)) {
> +            r = rados_conf_set(s->cluster, "rbd_cache_max_dirty", "0");
> +            if (r < 0) {
> +                rados_conf_set(s->cluster, "rbd_cache", "false");
> +            }
> +        }
> +    }

Last time I looked at ceph, rbd_flush was not a full flush of the cache;
it only ensured that the pending requests were sent.  So my questions are:

1) has this changed?  does rbd_flush now flush dirty items when
rbd_cache_max_dirty > 0?

2) should the usage of a cache be conditional on LIBRBD_VERSION_CODE >=
LIBRBD_VERSION(0, 1, 1)?

Thanks,

Paolo