[Libguestfs] [nbdkit PATCH v3 14/15] todo: Mention possibility of caching .can_FOO callbacks

[Richard W.M. Jones]

On Thu, Mar 08, 2018 at 05:03:10PM -0600, Eric Blake wrote:
> Recent patches clarified documentation to point out that within
> the life of a single connection, the .can_FOO helpers should
> return consistent results, and that callers may cache those
> results.  But at least in the case of .can_fua, we aren't really
> caching things; depending on the overhead involved, calling out
> to the plugin's .can_fua on every .pwrite with FUA requested
> may be noticeable overhead compared to caching it.  Any cache
> must not be a static variable, as it can differ between
> connections.
> 
> Signed-off-by: Eric Blake <eblake at redhat.com>
> ---
>  TODO | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/TODO b/TODO
> index b6fb0b1..1e0f483 100644
> --- a/TODO
> +++ b/TODO
> @@ -40,6 +40,10 @@ General ideas for improvements
>    ones like offset) can fail to initialize if they can't guarantee
>    strict alignment and don't want to deal with bounce buffers.
> 
> +* Add per-connection caching of .can_FOO callbacks (we already have
> +  some: .can_write is only called once, but .can_fua is called on
> +  every request with the FUA flag set).
> +
>  Suggestions for plugins
>  -----------------------
> 

ACK series up to and including this patch.

I've got some comments on the final (RFC) patch.

Rich.

-- 
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