Robert Watson wrote:
On Fri, 29 Sep 2006, Andre Oppermann wrote:
The patch is available here:
http://people.freebsd.org/~andre/sosend+m_uiotombuf-20060928.diff
I like the concept of these changes in principle -- this is the reason I
broke out sosend_copyin(), so that we could start plugging bits of the
send routines more easily for optimization. However, I think we need to
review this really carefully. A casual glance brought up one question,
and I hope to get a chance to review this in detail in the next few
days. The question is with regard to the 'space' variable. When
breaking out sosend_copyin(), I originally simply passed space in as an
argument, which is what you do currently. However, I found I had to
change it to pass in the variable by reference so that it could be
updated, as later portions of sosend() depend on it being updated in
order to figure out what flags to pass to pru_send() with respect to
PRUS_MORETOCOME, as well as for the (resid && space > 0) condition for
the main loop. In your revised version, 'space' isn't updated in
sosend() after calling m_uiotombuf(), which on a casual read, suggests
that PRUS_MORETOCOME will no longer get set on the last pass into
pru_send(), and that the loop may go an extra time and pass more data
into TCP than there is room in the socket send buffer. I may be reading
wrong, I've not had time to look in any detail, but that was my
experience, so you may find you need to pass send by reference, as I do
in sosend_copyin(), for the same reason.
Your observation is correct. The variable 'space' is no longer updated
with my changes. For sosend_dgram() this is of no consequence as PRUS_
MORETOCOME can't ever be true. For datagrams the uio must not contain
more data than we have space left in the socket buffer. Otherwise we
fail with EMSGSIZE. For sosend_generic() PRUS_MORETOCOME is no longer
correctly set with my changes. For TCP this is of no consequence either
as TCP doesn't care about it. For correctness I'll change my patch to
update 'space' in sosend_generic() and remove the PRUS_MORETOCOME flag
from sosend_dgram() completely.
--
Andre
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