Change the curvnet variable from a global const struct vnet *,

previously always pointing to the default vnet context, to a
dynamically changing thread-local one.  The currvnet context
should be set on entry to networking code via CURVNET_SET() macros,
and reverted to previous state via CURVNET_RESTORE().  Recursions
on curvnet are permitted, though strongly discuouraged.

This change should have no functional impact on nooptions VIMAGE
kernel builds, where CURVNET_* macros expand to whitespace.

The curthread->td_vnet (aka curvnet) variable's purpose is to be an
indicator of the vnet context in which the current network-related
operation takes place, in case we cannot deduce the current vnet
context from any other source, such as by looking at mbuf's
m->m_pkthdr.rcvif->if_vnet, sockets's so->so_vnet etc.  Moreover, so
far curvnet has turned out to be an invaluable consistency checking
aid: it helps to catch cases when sockets, ifnets or any other
vnet-aware structures may have leaked from one vnet to another.

The exact placement of the CURVNET_SET() / CURVNET_RESTORE() macros
was a result of an empirical iterative process, whith an aim to
reduce recursions on CURVNET_SET() to a minimum, while still reducing
the scope of CURVNET_SET() to networking only operations - the
alternative would be calling CURVNET_SET() on each system call entry.
In general, curvnet has to be set in three typicall cases: when
processing socket-related requests from userspace or from within the
kernel; when processing inbound traffic flowing from device drivers
to upper layers of the networking stack, and when executing
timer-driven networking functions.

This change also introduces a DDB subcommand to show the list of all
vnet instances.

Approved by:	julian (mentor)

1 files changed, 6 insertions, 0 deletions

diff --git a/sys/kern/kern_fork.c b/sys/kern/kern_fork.c
index e7e98b1..76695e7 100644
--- a/sys/kern/kern_fork.c
+++ b/sys/kern/kern_fork.c
@@ -68,6 +68,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/sdt.h>
 #include <sys/sx.h>
 #include <sys/signalvar.h>
+#include <sys/vimage.h>
 
 #include <security/audit/audit.h>
 #include <security/mac/mac_framework.h>
@@ -523,6 +524,11 @@ again:
 	td2->td_sigmask = td->td_sigmask;
 	td2->td_flags = TDF_INMEM;
 
+#ifdef VIMAGE
+	td2->td_vnet = NULL;
+	td2->td_vnet_lpush = NULL;
+#endif
+
 	/*
 	 * Duplicate sub-structures as needed.
 	 * Increase reference counts on shared objects.