sosend was attempting to reserve space in an mbuf cluster for a datagram
header and because of bugs in the sosend's mbuf allocation algorithm,
sosend was calling uiomove twice as many times as was necessary. It turns
out that PREPEND does the right thing when a cluster is associated with
an mbuf header, so the datagram header allocation can be defered. This
also ends up additionally consuming one less mbuf for the TCP protocol
because TCP always allocates another header mbuf regardless if space is
available to prepend the protocol header. The net result of this fix is
that unix domain and pipe throughput is increased by a measured 10%.
SUMMARY:
Here is a patch for a kernel hang that can be provoked with a write
or send of a negative amount. The talk program is capable of exercising
this bug. This patch also includes a fix for a bug that caused data
to be delivered to TCP in smaller chunks than desired, and which caused
TCP to send a short packet when starting up. Finally, there is a bug
fix for MSG_PEEK with an oobmark pending.
* Yuval Yarom's socket recv(2) fixes, to prevent incorrect blocking and
lack thereof with recv(2) and MSG_WAITALL. Fixes a sbdrop() panic during
some MSG_WAITALL recv(2) sleeps. Access rights fix (also in
uipc_syscalls.c) too. A test program which shows these problems is
available.
cgd