Does FreeBSD have sendmmsg or recvmmsg system calls?

[Luigi Rizzo]

On Thu, Jan 7, 2016 at 11:28 AM, Konstantin Belousov
<kostikbel at gmail.com> wrote:
> On Thu, Jan 07, 2016 at 10:31:13AM -0800, Luigi Rizzo wrote:
>> While it was good to have the first patch as a reminder of what needs to be done
>> (noticeably, discuss the various pieces to be modified and how to deal
>> with errors and the comments about DoS and malloc), I think that at
>> the moment it is premature to implement either the library functions
>> or the syscalls.
>>
>> What we need first is experimental data that shows a performance benefit
>> compared to looping around the single-packet syscall. Then we can decide
>> how to proceed.
> This is about performance.
>
>>
>> Implementing the library function now is relatively pointless: its only use
>> would be to compile some software that requires *mmsg() , and we can address
>> that with a custom patch for the application (which almost surely would
>> need to work around another ton of linux-specific functions).
> And this is about compatibility.  I agree with the statement above about
> the work with the performance motivation, but I do not agree that we should
> not ensure compatibility because there is more to do.  We have willing
> contributor, who learns, and who is on track to provide a usable
> implementation for the compat shims, be it in userspace or kernel (I do
> prefer userspace implementation).
>
> I do not understand you point that we can patch application.  IMO it
> is not a useful or scalable approach to handle changing app expectations
> from the base platform.

The libc API obviously needs to be conforming to the existing
sendmmsg/recvmmsg. I thought your point was that the underlying
syscall might possibly need a different set of parameters, so we could
as well experiment a bit to see what is needed before freezing it.

Regarding patching the application(s): of course it is not scalable
if there are many applications that will refuse to compile if
the *mmsg() functions are absent. However I expect this set of
application to be minuscule if not empty, and if they exist they
are probably plagued by other portability issues.

So (and using *mmsg() vs *msg() is about performance) I think that
until we have an underlying performant implementation of the *mmsg()
calls, there is no urgency in implementing the libc functions,
because we might later have to change then libc->syscall wrapper
anyways.

cheers
luigi