K 10
svn:author
V 5
andre
K 8
svn:date
V 27
2012-11-10T21:09:17.255857Z
K 7
svn:log
V 1015
Add m_uiotosfmbuf() which turns a uio iovec array into a chain
of mbuf's with sfbuffers attaches to it.  sfbuffers in turn directly
reference and hold the VM page.  Once traveled through the stack
the NIC then directly DMA's the data from the userspace VM pages.

The referenced pages are protected from going aways but no from
concurrent modification by the application.  If data in the page
is modified while the mbuf/sfbuf is still waiting in a queue to
the sent, the modified data will be sent.  Additionally certain
cache and memory coherence effects may come into play resulting
in unpredictably in whether the old or new data will go out
eventually.  This is the same as with sendfile(2) where the
application also should not modify the backing file while sending.

It is the equivalent to m_uiotombuf() which does a normal copyin.

It is the first step for a new send side zero copy implementation.

This checkpoints a work in progress, isn't complete and likely
has evil bugs or poorly handled edge cases.

END