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SubjectRe: [RFC PATCH 1/6] virtio/console: Add splice_write support
On (Tue) 24 Jul 2012 [11:37:07], Yoshihiro YUNOMAE wrote:
> From: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
>
> 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 <masami.hiramatsu.pt@hitachi.com>
> Cc: Amit Shah <amit.shah@redhat.com>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---

> +/* 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


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