title: Why no zero-copy networking in linux kernel?
body: <p>I'd like to know the reasons for why the linux kernel (or any other mainstream OS) does not have a feature for zero copy networking ? By zero copy I mean, that an packet/datastream does not get copied for passing to an application in userspace but e.g. uses a memory-pool type of allocator to share the memory between kernel and userspace. I've came up with 3 theory's on my own:</p>
  
  <p>a) I guess there are security concerns. But is there really no way of making memory shared securily between userspace and kernel when they are just used as a buffer ?</p>
  
  <p>b) I guess there are stability concerns. But can't we assume that whoever uses zero-copy networking and e.g. needs to instanciate and pass a memory-pool for the kernel call is aware of memory management? Aware enough to avoid leaks ?</p>
  
  <p>c) It just haven't been done/needed so far. I can't really imagine that nobody requested this feature, as everybody who is using small packet sizes is typically bottlenecked by the "slow" TCP-stack implementation and there are 3rd party tools out there offered for 0-copy networking for usage with special network cards.</p>
  
  <p>Feel free to post any guesses, but please mark whether you are assuming or have a deeper knowledge of the reasons to keep StackOverflow-quality :-)</p>