Re: [PATCH v2] proto: add xNBD command NBD_CMD_CACHE to the spec
Hi Eric,
Sorry for not following up on this sooner (and thanks for nudging me)
On Thu, May 03, 2018 at 05:07:47PM -0500, Eric Blake wrote:
[...]
> diff --git a/doc/proto.md b/doc/proto.md
> index 32a36ba..09bfc92 100644
> --- a/doc/proto.md
> +++ b/doc/proto.md
> @@ -1060,6 +1060,10 @@ The field has the following format:
> the export.
> - bit 9, `NBD_FLAG_SEND_RESIZE`: defined by the experimental `RESIZE`
> [extension](https://github.com/NetworkBlockDevice/nbd/blob/extension-resize/doc/proto.md).
> +- bit 10, `NBD_FLAG_SEND_CACHE`: documents that the server understands
> + `NBD_CMD_CACHE`; however, note that a server MAY support the command
> + even without advertising this bit, and conversely that this bit does
> + not guarantee that the command will succeed or have an impact.
I think that rather than rubber-stamping "let's send things and see what
happens", it makes more sense to document that there are current
implementations which do work that way, but that we don't recommend
that. As in:
(...); however, note that implementations exist which support the
command even without advertising this bit (...)
In the long term, I would prefer that we don't add new implementations
which behave in this manner, while not immediately causing the existing
implementation (i.e., xnbd) to suddenly no longer be compliant. This
wording does do that.
[...]
> +* `NBD_CMD_CACHE` (5)
[...]
> + A client MAY attempt to send a cache request even when
> + `NBD_FLAG_SEND_CACHE` was not set in the transmission flags field,
"Note that client implementations exist which attempt to send a cache
request even when (...)"
> + however, in that case, it MUST NOT use any command flags. A
"but these implementations do not use any command flags."
other than that, looks good to me.
--
Could you people please use IRC like normal people?!?
-- Amaya Rodrigo Sastre, trying to quiet down the buzz in the DebConf 2008
Hacklab
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