Re: [Scst-devel] scst_user handler

[Bart V. A. <bva...@ac...>]

On Mon, Feb 27, 2012 at 8:17 AM, Subranshu Patel - ERS, HCL Tech <
Sub...@hc...> wrote:

>   ** **
>
> Suppose I am not using the put_page_callback patch.****
>
> ** **
>
> In case of kernel device handler, sock->ops->sendpage is invoked (zero
> copy); in case of userspace handler (scst_user) sock_no_sendpage is
> invoked. sock_no_sendpage invokes kernel_sendmsg which means an additional
> copy of data.****
>
> ** **
>
> **1.  **What is the reason that if we use kernel device handler, the
> buffer is not freed or reused until sendpage completes sending data? ****
>
> Because sendpage() invokes get_page() before returning and put_page()
after sending finished.

Bart.