Kernel Trap has a great interview with the maintainer of the Linux Block IO layer. He discusses some of the limitations in the current I/O schedulers, and how they can be swapped out dynamically at runtime. I found the following particularly informative: “Splice has a host of applications. It can completely replace the bad hack that is sendfile(), which is an extremely limited zero copy interface for sending a file over the network. The neat thing about using pipes as the buffers, is that you have a known interface to work with and a way to tie things together intuitively. A good and easy to understand example is a live TV setup, where you have a driver for your TV encoder (lets call that /dev/tvcapture) and a driver for your TV decoder (lets call that /dev/tvout. Say you want to watch live TV while storing the contents to a file for pausing or rewind purposes, you could describe that as easy as:”
$ splice-in /dev/tvcapture | splice-tee out.mpg | splice-out /dev/tvout
“The first step will open /dev/tvcapture and splice that file descriptor to STDOUT. The second will duplicate the page references from the STDIN pipe, splicing the first to the output file and splicing the second to STDOUT. Finally, the last step will splice STDIN to a file descriptor for /dev/tvout. The data never needs to be copied around, we simply move page references around inside the kernel. It’s like building with Lego blocks :-)”