Re: splice question

[Linus Torvalds <torvalds@linux-foundation.org>]

On Sun, 12 Aug 2007, David H?rdeman wrote:
> 
> Once the data is in the pipe, my idea was to tee() from the pipe to each
> client socket using nonblocking ops, and then consume the data by splicing it
> to /dev/null.
> 
> The problem is that tee() doesn't support sockets. Is this a limitation that
> would be easy to fix?

It's very intentional. 

You should think of "tee()" as a memcpy() on kernel buffers.

And what are kernel buffers? It's not a socket.

The "kernel buffer" is simply just another name for a pipe.

So tee() *duplicates* the data in pipe, and then you can use "splice()" on 
the duplicated data to actually send it off somewhere else (eg a socket).

(Or any other pipe operation, for that matter - you can read() it into 
user space etc).

> Otherwise I guess I'd have to add a second pipe, then (in a loop)
> tee() from the first to the second pipe and then splice from the second pipe
> to a socket. Doesn't sound very elegant and would need quite a lot of extra
> syscalls.

You really should think of this as a memcpy(), and you'll be in the right 
mindframe. The system calls themselves are cheap.

			Linus