Re: [PATCH v5 1/6] QIOChannel: Add io_writev_zerocopy & io_flush_zerocopy callbacks

["Daniel P. Berrangé" <berrange@redhat.com>]

On Fri, Nov 12, 2021 at 02:10:36AM -0300, Leonardo Bras wrote:
> Adds io_writev_zerocopy and io_flush_zerocopy as optional callback to QIOChannelClass,
> allowing the implementation of zerocopy writes by subclasses.
> 
> How to use them:
> - Write data using qio_channel_writev_zerocopy(),
> - Wait write completion with qio_channel_flush_zerocopy().
> 
> Notes:
> As some zerocopy implementations work asynchronously, it's
> recommended to keep the write buffer untouched until the return of
> qio_channel_flush_zerocopy(), to avoid the risk of sending an updated
> buffer instead of the one at the write.
> 
> As the new callbacks are optional, if a subclass does not implement them, then:
> - io_writev_zerocopy will return -1,
> - io_flush_zerocopy will return 0 without changing anything.
> 
> Also, some functions like qio_channel_writev_full_all() were adapted to
> receive a flag parameter. That allows shared code between zerocopy and
> non-zerocopy writev.
> 
> Signed-off-by: Leonardo Bras <leobras@redhat.com>
> ---
>  include/io/channel.h | 93 ++++++++++++++++++++++++++++++++++++++------
>  io/channel.c         | 65 +++++++++++++++++++++++++------
>  2 files changed, 135 insertions(+), 23 deletions(-)
> 

> +/**
> + * qio_channel_flush_zerocopy:
> + * @ioc: the channel object
> + * @errp: pointer to a NULL-initialized error object
> + *
> + * Will block until every packet queued with
> + * qio_channel_writev_zerocopy() is sent, or return
> + * in case of any error.
> + *
> + * Returns -1 if any error is found, 0 otherwise.

  Returns -1 if any error is found, 0 if all data was sent,
           or 1 if all data was sent but at least some was copied.


> + * If not implemented, acts as a no-op, and returns 0.
> + */
> +
> +int qio_channel_flush_zerocopy(QIOChannel *ioc,
> +                               Error **errp);

Regards,
Daniel
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