Re: [Qemu-devel] [RFC PATCH 1/6] virtio/console: Add splice_write support

[Amit Shah]

On (Tue) 24 Jul 2012 [11:37:07], Yoshihiro YUNOMAE wrote:
> From: Masami Hiramatsu <address@hidden>
> 
> Enable to use splice_write from pipe to virtio-console port.
> This steals pages from pipe and directly send it to host.
> 
> Note that this may accelerate only the guest to host path.
> 
> Signed-off-by: Masami Hiramatsu <address@hidden>
> Cc: Amit Shah <address@hidden>
> Cc: Arnd Bergmann <address@hidden>
> Cc: Greg Kroah-Hartman <address@hidden>
> ---

> +/* Faster zero-copy write by splicing */
> +static ssize_t port_fops_splice_write(struct pipe_inode_info *pipe,
> +                                   struct file *filp, loff_t *ppos,
> +                                   size_t len, unsigned int flags)
> +{
> +     struct port *port = filp->private_data;
> +     struct sg_list sgl;
> +     ssize_t ret;
> +     struct splice_desc sd = {
> +             .total_len = len,
> +             .flags = flags,
> +             .pos = *ppos,
> +             .u.data = &sgl,
> +     };
> +
> +     sgl.n = 0;
> +     sgl.len = 0;
> +     sgl.sg = kmalloc(sizeof(struct scatterlist) * MAX_SPLICE_PAGES,
> +                      GFP_ATOMIC);

Do you expect this function to be called from interrupt context?

> +     if (unlikely(!sgl.sg))
> +             return -ENOMEM;
> +
> +     sg_init_table(sgl.sg, MAX_SPLICE_PAGES);
> +     ret = __splice_from_pipe(pipe, &sd, pipe_to_sg);
> +     if (likely(ret > 0))
> +             ret = send_pages(port, sgl.sg, sgl.n, sgl.len, true);
> +
> +     return ret;
> +}

                Amit