On Thu, Oct 26, 2017 at 09:42:46AM -0600, David Ahern wrote: > On 10/26/17 9:33 AM, Phil Sutter wrote: > > 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? > > MSG_TRUNC returns the actual message length if it is greater than the > buffer. The message was dequeued and what could be copied into the > supplied buffer is copied, but that means the returned message is truncated.
Ah, so one would have to resend the request then. Stupid me. :) Thanks, Phil
