VNET(9) FreeBSD Kernel Developer's Manual VNET(9)
NAME
VNET - network subsystem virtualization infrastructure
SYNOPSIS
options VIMAGE
options VNET_DEBUG
#include <net/vnet.h>
Constants and Global Variables
VNET_SETNAME VNET_SYMPREFIX
extern struct vnet *vnet0;
Variable Declaration
VNET(name);
VNET_NAME(name);
VNET_DECLARE(type, name);
VNET_DEFINE(type, name);
VNET_DEFINE_STATIC(type, name);
#define V_name VNET(name)
Virtual Instance Selection
CRED_TO_VNET(struct ucred *);
TD_TO_VNET(struct thread *);
P_TO_VNET(struct proc *);
IS_DEFAULT_VNET(struct vnet *);
VNET_ASSERT(exp, msg);
CURVNET_SET(struct vnet *);
CURVNET_SET_QUIET(struct vnet *);
CURVNET_RESTORE();
VNET_ITERATOR_DECL(struct vnet *);
VNET_FOREACH(struct vnet *);
Locking
VNET_LIST_RLOCK();
VNET_LIST_RUNLOCK();
VNET_LIST_RLOCK_NOSLEEP();
VNET_LIST_RUNLOCK_NOSLEEP();
Startup and Teardown Functions
struct vnet *
vnet_alloc(void);
void
vnet_destroy(struct vnet *);
VNET_SYSINIT(ident, enum sysinit_sub_id subsystem,
enum sysinit_elem_order order, sysinit_cfunc_t func,
const void *arg);
VNET_SYSUNINIT(ident, enum sysinit_sub_id subsystem,
enum sysinit_elem_order order, sysinit_cfunc_t func,
const void *arg);
Eventhandlers
VNET_GLOBAL_EVENTHANDLER_REGISTER(const char *name, void *func,
void *arg, int priority);
VNET_GLOBAL_EVENTHANDLER_REGISTER_TAG(eventhandler_tag tag,
const char *name, void *func, void *arg, int priority);
Sysctl Handling
SYSCTL_VNET_INT(parent, nbr, name, access, ptr, val, descr);
SYSCTL_VNET_PROC(parent, nbr, name, access, ptr, arg, handler, fmt,
descr);
SYSCTL_VNET_STRING(parent, nbr, name, access, arg, len, descr);
SYSCTL_VNET_STRUCT(parent, nbr, name, access, ptr, type, descr);
SYSCTL_VNET_UINT(parent, nbr, name, access, ptr, val, descr);
VNET_SYSCTL_ARG(req, arg1);
DESCRIPTION
VNET is the name of a technique to virtualize the network stack. The
basic idea is to change global resources most notably variables into per
network stack resources and have functions, sysctls, eventhandlers, etc.
access and handle them in the context of the correct instance. Each
(virtual) network stack is attached to a prison, with vnet0 being the
unrestricted default network stack of the base system.
The global defines for VNET_SETNAME and VNET_SYMPREFIX are shared with
kvm(3) to access internals for debugging reasons.
Variable Declaration
Variables are virtualized by using the VNET_DEFINE() macro rather than
writing them out as type name. One can still use static initialization,
e.g.,
VNET_DEFINE(int, foo) = 1;
Variables declared with the static keyword can use the
VNET_DEFINE_STATIC() macro, e.g.,
VNET_DEFINE_STATIC(SLIST_HEAD(, bar), bars);
Static initialization is not possible when the virtualized variable would
need to be referenced, e.g., with "TAILQ_HEAD_INITIALIZER()". In that
case a VNET_SYSINIT() based initialization function must be used.
External variables have to be declared using the VNET_DECLARE() macro.
In either case the convention is to define another macro, that is then
used throughout the implementation to access that variable. The variable
name is usually prefixed by V_ to express that it is virtualized. The
VNET() macro will then translate accesses to that variable to the copy of
the currently selected instance (see the Virtual instance selection
section):
#define V_name VNET(name)
NOTE: Do not confuse this with the convention used by VFS(9).
The VNET_NAME() macro returns the offset within the memory region of the
virtual network stack instance. It is usually only used with
SYSCTL_VNET_*() macros.
Virtual Instance Selection
There are three different places where the current virtual network stack
pointer is stored and can be taken from:
1. a prison:
(struct prison *)->pr_vnet
For convenience the following macros are provided:
CRED_TO_VNET(struct ucred *)
TD_TO_VNET(struct thread *)
P_TO_VNET(struct proc *)
2. a socket:
(struct socket *)->so_vnet
3. an interface:
(struct ifnet *)->if_vnet
In addition the currently active instance is cached in
"curthread->td_vnet" which is usually only accessed through the curvnet
macro.
To set the correct context of the current virtual network instance, use
the CURVNET_SET() or CURVNET_SET_QUIET() macros. The CURVNET_SET_QUIET()
version will not record vnet recursions in case the kernel was compiled
with options VNET_DEBUG and should thus only be used in well known cases,
where recursion is unavoidable. Both macros will save the previous state
on the stack and it must be restored with the CURVNET_RESTORE() macro.
NOTE: As the previous state is saved on the stack, you cannot have
multiple CURVNET_SET() calls in the same block.
NOTE: As the previous state is saved on the stack, a CURVNET_RESTORE()
call has to be in the same block as the CURVNET_SET() call or in a
subblock with the same idea of the saved instances as the outer block.
NOTE: As each macro is a set of operations and, as previously explained,
cannot be put into its own block when defined, one cannot conditionally
set the current vnet context. The following will not work:
if (condition)
CURVNET_SET(vnet);
nor would this work:
if (condition) {
CURVNET_SET(vnet);
}
CURVNET_RESTORE();
Sometimes one needs to loop over all virtual instances, for example to
update virtual from global state, to run a function from a callout(9) for
each instance, etc. For those cases the VNET_ITERATOR_DECL() and
VNET_FOREACH() macros are provided. The former macro defines the
variable that iterates over the loop, and the latter loops over all of
the virtual network stack instances. See Locking for how to savely
traverse the list of all virtual instances.
The IS_DEFAULT_VNET() macro provides a safe way to check whether the
currently active instance is the unrestricted default network stack of
the base system (vnet0).
The VNET_ASSERT() macro provides a way to conditionally add assertions
that are only active with options VIMAGE compiled in and either options
VNET_DEBUG or options INVARIANTS enabled as well. It uses the same
semantics as KASSERT(9).
Locking
For public access to the list of virtual network stack instances e.g., by
the VNET_FOREACH() macro, read locks are provided. Macros are used to
abstract from the actual type of the locks. If a caller may sleep while
traversing the list, it must use the VNET_LIST_RLOCK() and
VNET_LIST_RUNLOCK() macros. Otherwise, the caller can use
VNET_LIST_RLOCK_NOSLEEP() and VNET_LIST_RUNLOCK_NOSLEEP().
Startup and Teardown Functions
To start or tear down a virtual network stack instance the internal
functions vnet_alloc() and vnet_destroy() are provided and called from
the jail framework. They run the publicly provided methods to handle
network stack startup and teardown.
For public control, the system startup interface has been enhanced to not
only handle a system boot but to also handle a virtual network stack
startup and teardown. To the base system the VNET_SYSINIT() and
VNET_SYSUNINIT() macros look exactly as if there were no virtual network
stack. In fact, if options VIMAGE is not compiled in they are compiled
to the standard SYSINIT() macros. In addition to that they are run for
each virtual network stack when starting or, in reverse order, when
shutting down.
Eventhandlers
Eventhandlers can be handled in two ways:
1. save the tags returned in each virtual instance and properly
free the eventhandlers on teardown using those, or
2. use one eventhandler that will iterate over all virtual
network stack instances.
For the first case one can just use the normal EVENTHANDLER(9) functions,
while for the second case the VNET_GLOBAL_EVENTHANDLER_REGISTER() and
VNET_GLOBAL_EVENTHANDLER_REGISTER_TAG() macros are provided. These
differ in that VNET_GLOBAL_EVENTHANDLER_REGISTER_TAG() takes an extra
first argument that will carry the tag upon return. Eventhandlers
registered with either of these will not run func directly but func will
be called from an internal iterator function for each vnet. Both macros
can only be used for eventhandlers that do not take additional arguments,
as the variadic arguments from an EVENTHANDLER_INVOKE(9) call will be
ignored.
Sysctl Handling
A sysctl(9) can be virtualized by using one of the SYSCTL_VNET_*()
macros.
They take the same arguments as the standard sysctl(9) functions, with
the only difference, that the ptr argument has to be passed as
`&VNET_NAME(foo)' instead of `&foo' so that the variable can be selected
from the correct memory region of the virtual network stack instance of
the caller.
For the very rare case a sysctl handler function would want to handle
arg1 itself the VNET_SYSCTL_ARG(req, arg1) is provided that will
translate the arg1 argument to the correct memory address in the virtual
network stack context of the caller.
SEE ALSO
jail(2), kvm(3), EVENTHANDLER(9), KASSERT(9), sysctl(9)
Marko Zec, Implementing a Clonable Network Stack in the FreeBSD Kernel,
USENIX ATC'03, June 2003, Boston
HISTORY
The virtual network stack implementation first appeared in FreeBSD 8.0.
AUTHORS
The VNET framework was designed and implemented at the University of
Zagreb by Marko Zec under sponsorship of the FreeBSD Foundation and NLnet
Foundation, and later extended and refined by Bjoern A. Zeeb (also under
FreeBSD Foundation sponsorship), and Robert Watson.
This manual page was written by Bjoern A. Zeeb, CK Software GmbH, under
sponsorship from the FreeBSD Foundation.
FreeBSD 13.1-RELEASE-p6 December 10, 2020 FreeBSD 13.1-RELEASE-p6
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