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


domain_add, pfctlinput, pfctlinput2, pffinddomain, pffindproto, pffindtype, DOMAIN_SETnetwork domain management


#include < sys/param.h>
#include < sys/kernel.h>
#include < sys/protosw.h>
#include < sys/domain.h>

domain_add( void *data);

pfctlinput( int cmd, struct sockaddr *sa);

pfctlinput2( int cmd, struct sockaddr *sa, void *ctlparam);

struct domain *
pffinddomain( int family);

struct protosw *
pffindproto( int family, int protocol, int type);

struct protosw *
pffindtype( int family, int type);

DOMAIN_SET( name);


Network protocols installed in the system are maintained within what are called domains (for example the inetdomain and localdomain).

struct domain { 
 int dom_family;  /* AF_xxx */ 
 char *dom_name; 
 void (*dom_init)  /* initialize domain data structures */ 
 void (*dom_destroy)  /* cleanup structures / state */ 
 int (*dom_externalize) /* externalize access rights */ 
  (struct mbuf *, struct mbuf **); 
 void (*dom_dispose)  /* dispose of internalized rights */ 
  (struct mbuf *); 
 struct protosw *dom_protosw, *dom_protoswNPROTOSW; 
 struct domain *dom_next; 
 int (*dom_rtattach)  /* initialize routing table */ 
  (void **, int); 
 int (*dom_rtdetach)  /* clean up routing table */ 
  (void **, int); 
 int dom_rtoffset;  /* an arg to rtattach, in bits */ 
 int dom_maxrtkey;  /* for routing layer */ 
 void *(*dom_ifattach)(struct ifnet *); 
 void (*dom_ifdetach)(struct ifnet *, void *); 
     /* af-dependent data on ifnet */ 

Each domain contains an array of protocol switch structures ( struct protosw *), one for each socket type supported.

struct protosw { 
 short pr_type;  /* socket type used for */ 
 struct domain *pr_domain; /* domain protocol a member of */ 
 short pr_protocol;  /* protocol number */ 
 short pr_flags;  /* see below */ 
/* protocol-protocol hooks */ 
 pr_input_t *pr_input;  /* input to protocol (from below) */ 
 pr_output_t *pr_output;  /* output to protocol (from above) */ 
 pr_ctlinput_t *pr_ctlinput; /* control input (from below) */ 
 pr_ctloutput_t *pr_ctloutput; /* control output (from above) */ 
/* utility hooks */ 
 pr_init_t *pr_init; 
 pr_destroy_t *pr_destroy; 
 pr_fasttimo_t *pr_fasttimo; /* fast timeout (200ms) */ 
 pr_slowtimo_t *pr_slowtimo; /* slow timeout (500ms) */ 
 pr_drain_t *pr_drain;  /* flush any excess space possible */ 
 struct pr_usrreqs *pr_usrreqs; /* supersedes pr_usrreq() */ 

The following functions handle the registration of a new domain, lookups of specific protocols and protocol types within those domains, and handle control messages from the system.

pfctlinput() is called by the system whenever an event occurs that could affect every domain. Examples of those types of events are routing table changes, interface shutdowns or certain ICMP message types. When called, pfctlinput() calls the protocol specific pr_ctlinput() function for each protocol in that has defined one, in every domain.

pfctlinput2() provides that same functionality of pfctlinput(), but with a few additional checks and a new void * argument that is passed directly to the protocol's pr_ctlinput() function. Unlike pfctlinput(), pfctlinput2() verifies that sa is not NULL, and that only the protocol families that are the same as sa have their pr_ctlinput() function called.

domain_add() adds a new protocol domain to the system. The argument data is cast directly to struct domain * within the function, but is declared void * in order to prevent compiler warnings when new domains are registered with SYSINIT(). In most cases domain_add() is not called directly, instead DOMAIN_SET() is used.

If the new domain has defined an initialization routine, it is called by domain_add(); as well, each of the protocols within the domain that have defined an initialization routine will have theirs called.

Once a domain is added it cannot be unloaded. This is because there is no reference counting system in place to determine if there are any active references from sockets within that domain.

pffinddomain() finds a domain by family. If the domain cannot be found, NULL is returned.

pffindtype() and pffindproto() look up a protocol by its number or by its type. In most cases, if the protocol or type cannot be found, NULL is returned, but pffindproto() may return the default if the requested type is SOCK_RAW, a protocol switch type of SOCK_RAW is found, and the domain has a default raw protocol.

Both functions are called by socreate() in order to resolve the protocol for the socket currently being created.

DOMAIN_SET() is a macro that simplifies the registration of a domain via SYSINIT(). The code resulting from the macro expects there to be a domain structure named “ namedomain” where name is the argument to DOMAIN_SET():

struct domain localdomain = 
{ AF_LOCAL, "local", unp_init, unp_externalize, unp_dispose, 
  localsw, &localsw[sizeof(localsw)/sizeof(localsw[0])] }; 


Both pffindtype() and pffindproto() return a struct protosw * for the protocol requested. If the protocol or socket type is not found, NULL is returned. In the case of pffindproto(), the default protocol may be returned for SOCK_RAW types if the domain has a default raw protocol.




This manual page was written by Chad David <davidc@acns.ab.ca>.
December 7, 2012 FreeBSD