On Mon, Jan 26, 2004 at 10:53:54AM -0800, Julian Elischer wrote:
...
> On Mon, 26 Jan 2004, Stuart Pook wrote:
>
> > > On 23 Jan 2004, Don Lewis wrote:
> > > > the send does not give an error: the packet is just thrown away.
> > >
> > > Which is the same result as you would get if the bottleneck is just one
> > > network hop away instead of at the local NIC.
> >
> > But it isn't. I'm broadcasting onto the local network. With Linux and
> > Solaris (which implement what FreeBSD send(2) says), it is so easy: I just
> > send(2) away, and because the send blocks when the kernel buffer space is
I'd be really curious to know how Linux/Solaris actually implement
this blocking send and if they really block or use some kind
of timeout/retry loop in the kernel.
To implement a blocking send() on UDP sockets, you need a different
driver model from the one we have, one where sockets and other data
sources trying to access a full interface queue should be queued
into some kind of list hanging off the interface, so that when the
interface is ready again you can wake up the pending clients in
turn and process their requests.
This would cause the output queue to become effectively
unbounded (basically, it is like reserving at least one slot
per socket -- more if you want to deal with fragments),
and even if the slot can be allocated as part of
the socket, the delay would become unbounded as well.
Secondly, if the interface for some reason goes "temporarily"
down (e.g. no-carrier or the like) the process would suddenly
block unless you mark the socket as non blocking.
cheers
luigi
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