On Thu, Oct 26, 2017 at 09:28:00AM -0600, David Ahern wrote: > On 10/26/17 4:24 AM, Stephen Hemminger wrote: > >> > >> The kernel needs a flag that says "give me the message of the buffer is > >> large enough; if not just PEEK and tell me the length." That would avoid > >> the double call in most cases. > > > > Actually this has little impact because old code was doing implicit zero > > of whole buffer, new code does not. > > > > The patch calls recvmsg twice; libnl does the same thing. It would be > better performance wise to have a flag that allows retrieval of the > message if the supplied buffer is large enough and PEEK semantics if > not. It was really a comment on how we could do better with proper > kernel support.
Doesn't MSG_TRUNC without MSG_PEEK do just that? Cheers, Phil
