Re: [splice PATCH 3/3] splice: added support for pipe-to-pipe splice()

[Vegard Nossum <vegard.nossum@gmail.com>]

2009/4/30 Max Kellermann <mk@cm4all.com>:
> This patch enables the splice() system call to copy buffers from one
> pipe to another.  This obvious and trivial use case for splice() was
> not supported until now.
>
> It reuses the functions link_ipipe_prep() and link_opipe_prep() from
> the tee() system call implementation.
>
> Signed-off-by: Max Kellermann <mk@cm4all.com>
> ---
>
>  fs/splice.c |  166 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 files changed, 166 insertions(+), 0 deletions(-)
>
> diff --git a/fs/splice.c b/fs/splice.c
> index 96135eb..f69a88f 100644
> --- a/fs/splice.c
> +++ b/fs/splice.c
> @@ -902,6 +902,156 @@ ssize_t generic_splice_sendpage(struct pipe_inode_info *pipe, struct file *out,
>
>  EXPORT_SYMBOL(generic_splice_sendpage);
>
> +static int link_ipipe_prep(struct pipe_inode_info *pipe, unsigned int flags);
> +static int link_opipe_prep(struct pipe_inode_info *pipe, unsigned int flags);
> +
> +/**
> + * Returns the nth pipe buffer after the current one.
> + *
> + * @i the buffer index, relative to the current one
> + */
> +static inline struct pipe_buffer *
> +pipe_buffer_at(struct pipe_inode_info *pipe, unsigned i)
> +{
> +       BUG_ON(i >= PIPE_BUFFERS);
> +
> +       return pipe->bufs + ((pipe->curbuf + i) & (PIPE_BUFFERS - 1));
> +}
> +
> +/**
> + * Splice pages from one pipe to another.
> + *
> + * @ipipe the input pipe
> + * @opipe the output pipe
> + * @len the maximum number of bytes to move
> + * @flags splice modifier flags
> + */
> +static long do_splice_pipes(struct pipe_inode_info *ipipe,
> +                           struct pipe_inode_info *opipe,
> +                           size_t len, unsigned int flags)
> +{
> +       struct pipe_buffer *ibuf, *obuf;
> +       long ret;
> +       int do_wakeup = 0;
> +
> +       if (ipipe == opipe)
> +               /* cannot splice a pipe to itself */
> +               return -EINVAL;
> +

What happens if you splice two pipes, in separate threads, to each other? :-)


Vegard