On Tue, 06 Jun 2017 15:02:45 +0200, "Frank Smith" said:

I want to use sendfile to send my images really fast over the network.

Step 0: Define "really fast". (I work with boxes that have LACP bonds of 2x40gbit ethernet interfaces - your v4l2 device is probably the slow link at that point, and sendfile won't matter). Step 1: Look at the performance of your v4l2 device and your network device, and determine whether sendfile is likely to resolve any actual bottleneck you're seeing. (Yes, as usual - before expending a lot of effort trying to make something work, spend a little time making sure you're solving the right problem)