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VNET(9)                FreeBSD Kernel Developer's Manual               VNET(9)

NAME
     VNET - network subsystem virtualization infrastructure

SYNOPSIS
     options VIMAGE
     options VNET_DEBUG

     #include <sys/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);

     #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
     or storage class specifiers, e.g.,

           static VNET_DEFINE(int, foo) = 1;
     or
           static VNET_DEFINE(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)

HISTORY
     The virtual network stack implementation first appeared in FreeBSD 8.0.

AUTHORS
     This manual page was written by Bjoern A. Zeeb, CK Software GmbH, under
     sponsorship from the FreeBSD Foundation.

FreeBSD 11.1-RELEASE-p4        November 20, 2014       FreeBSD 11.1-RELEASE-p4
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