Manual sysctlmibinfo2

Posted on 2019-12-09 - Updated on 2021-02-26

The sysctlmibinfo2 library provides an API to explore the FreeBSD sysctl MIB and to get the info of an object, it is useful to build a sysctl-like tool to get or set the kernel state. For example, sysctlview, a graphical sysctl MIB explorer, depends on it.

This is the manual page, for a description, examples and FAQ:

SYSCTLMIBINFO2(3)      FreeBSD Library Functions Manual      SYSCTLMIBINFO2(3)

     SYSCTLMIF_VERSION, sysctlmif_name, sysctlmif_oidbyname,
     sysctlmif_oidextendedbyname, sysctlmif_desc, sysctlmif_descbyname,
     sysctlmif_label, sysctlmif_labelbyname, sysctlmif_fmt,
     sysctlmif_fmtbyname, sysctlmif_hashandler, sysctlmif_hashandlerbyname,
     sysctlmif_kind, sysctlmif_kindbyname, SYSCTLMIF_KINDTYPE,
     SYSCTLMIF_KINDFLAGS, sysctlmif_nextnode, sysctlmif_nextnodebyname,
     sysctlmif_nextleaf, sysctlmif_nextleafbyname, sysctlmif_object,
     sysctlmif_objectbyname, sysctlmif_freeobject, sysctlmif_list,
     sysctlmif_grouplist, sysctlmif_grouplistbyname, sysctlmif_leaves,
     sysctlmif_leavesbyname, sysctlmif_freelist, sysctlmif_tree,
     sysctlmif_treebyname, sysctlmif_freetree, sysctlmif_mib,
     sysctlmif_freemib - sysctl MIB-Tree API

     To load the required kernel modules at boot time, place the following
     lines in loader.conf(5):


     library "libsysctlmibinfo2"

     #include <sysctlmibinfo2.h>


     sysctlmif_name(int *id, size_t idlevel, char *name, size_t *namelen);

     sysctlmif_oidbyname(const char *name, int *id, size_t *idlevel);

     sysctlmif_oidextendedbyname(const char *name, int *id, size_t *idlevel);

     sysctlmif_desc(int *id, size_t idlevel, char *desc, size_t *desclen);

     sysctlmif_descbyname(const char *name, char *desc, size_t *desclen);

     sysctlmif_label(int *id, size_t idlevel, char *label, size_t *labellen);

     sysctlmif_labelbyname(const char *name, char *label, size_t *labellen);

     sysctlmif_fmt(int *id, size_t idlevel, char *fmt, size_t *fmtlen);

     sysctlmif_fmtbyname(const char *name, char *fmt, size_t *fmtlen);

     sysctlmif_hashandler(int *id, size_t idlevel, bool *handler);

     sysctlmif_hashandlerbyname(const char *name, bool *handler);

     sysctlmif_kind(int *id, size_t idlevel, unsigned int *kind);

     sysctlmif_kindbyname(const char *name, unsigned int *kind);

     unsigned int
     SYSCTLMIF_KINDTYPE(unsigned int kind);

     unsigned int
     SYSCTLMIF_KINDFLAGS(unsigned int kind);

     sysctlmif_nextleaf(int *id, size_t idlevel, int *idnext,
         size_t *idnextlevel);

     sysctlmif_nextleafbyname(const char *name, char *next, size_t *nextlen);

     sysctlmif_nextnode(int *id, size_t idlevel, int *idnext,
         size_t *idnextlevel);

     sysctlmif_nextnodebyname(const char *name, char *next, size_t *nextlen);

     struct sysctlmif_object *
     sysctlmif_object(int *id, size_t idlevel);

     struct sysctlmif_object *
     sysctlmif_objectbyname(const char *name);

     sysctlmif_freeobject(struct sysctlmif_object *object);

     struct sysctlmif_list *

     struct sysctlmif_list *
     sysctlmif_grouplist(int *idroot, size_t idrootlen);

     struct sysctlmif_list *
     sysctlmif_grouplistbyname(const char *name);

     struct sysctlmif_list *
     sysctlmif_leaves(int *idroot, size_t idrootlen);

     struct sysctlmif_list *
     sysctlmif_leavesbyname(const char *name);

     sysctlmif_freelist(struct sysctlmif_list *list);

     struct sysctlmif_object *
     sysctlmif_tree(int *idroot, size_t idrootlevel);

     struct sysctlmif_object *
     sysctlmif_treebyname(const char *name);

     sysctlmif_freetree(struct sysctlmif_object *node);

     struct sysctlmif_list *

     sysctlmif_freemib(struct sysctlmif_list *mib);

     The sysctlmibinfo2 library is an interface to the kernel sysctl MIB-Tree.
     It implements wrappers around the sysctlinfo(4) interface and
     sysctlbyname-improved to explore the sysctl MIB and to get the info of an
     object, moreover it defines a struct sysctlmif_object and provides a
     convenient API to build data structures of sysctlmif_object; as it is not
     designed to get and set object values, anyone wishing to do this should
     see sysctl(3).

     An object is identified by an Object Identifier (OID), a series of
     numbers, represented by a pair int *id and size_t idlevel, the level
     should be between 1 and CTL_MAXNAME.  It is possible to replace a number
     with a string to obtain an object name, e.g., [1.1] -> "kern.ostype".

     SYSCTLMIF_VERSION is set to 2 to differentiate between this library and

     sysctlmif_name() sets name and namelen like the object with id / idlevel.

     sysctlmif_desc(), sysctlmif_fmt() and sysctlmif_label() set desc and
     desclen, fmt and fmtlen, label and labellen like the object with id /
     idlevel.  sysctlmif_descbyname(), sysctlmif_fmtbyname() and
     sysctlmif_labelbyname() are equivalent but the object is identified by
     its name.

     sysctlmif_kind() and sysctlmif_kindbyname() set kind like the object with
     id / idlevel or name, it represents the object type and flags, defined in
     <sys/sysctl.h>.  Macros to deal with kind:
           SYSCTLMIF_KINDFLAGS(kind) returns flags,
           SYSCTLMIF_KINDTYPE(kind) returns type.

     sysctlmif_nextleaf() and sysctlmif_nextnode() set nextid and nextidlevel
     like the next leaf or also internal node visited in a "Depth First
     Traversal" of the object id / idlevel.

     sysctlmif_nextleafbyname() and sysctlmif_nextnodebyname() set next and
     nextlen like the next leaf or also internal node visited in a "Depth
     First Traversal" of the object name.

     sysctlmif_oidbyname() and sysctlmif_oidextendedbyname() set id and
     idlevel like the object with name, sysctlmif_oidextendedbyname() can
     convert a name extended with an input for the handler of a CTLTPYE_NODE,
     e.g., "<input>" -> [1.14.1.<input>].

     The previous functions seek the object with id / idlevel or name, then
     the property is copied into the buffer (e.g., desc, label, idnext, etc.).
     Before the call buflen (e.g., desclen, lebellen, idnextlevel, etc.)
     gives the size of buffer, after a successful call buflen gives the amount
     of data copied; the size of the property can be determined with the NULL
     argument for the buffer, the size will be returned in the location
     pointed to by buflen.

   sysctlmif_object API
     The sysctlmibinfo2 library defines a struct for the info of an object:

           SLIST_HEAD(sysctlmif_list, sysctlmif_object);

           struct sysctlmif_object {
                   SLIST_ENTRY(sysctlmif_object) object_link;
                   int      *id;            /* array of idlevel entries  */
                   size_t   idlevel;        /* between 1 and CTL_MAXNAME */
                   char     *name;          /* name in MIB notation      */
                   char     *desc;          /* description               */
                   char     *label;         /* aggregation label         */
                   uint8_t  type;           /* defined in <sys/sysctl.h> */
                   uint32_t flags;          /* defined in <sys/sysctl.h> */
                   char     *fmt;           /* format string             */
                   struct sysctlmif_list *children; /* children list     */

     and a list of objects, struct sysctlmif_list, iterable by the SLIST
     macros, see queue(3) and EXAMPLES.

     sysctlmif_object() and sysctlmif_objectbyname() return a pointer to the
     allocated memory for a struct sysctlmif_object of the object with id /
     idlevel or name, the pointer can be passed to sysctlmif_freeobject() to
     free the memory.

     sysctlmif_list() allocates memory and returns a list with all the objects
     of the MIB, sysctlmif_freelist() frees the allocated memory.

     sysctlmif_grouplist() and sysctlmif_grouplistbyname() allocate memory and
     return a list of the objects, internal nodes and leaves, visited in a
     "Depth First Traversal", id / idlevel or name denote the root,
     sysctlmif_freelist() frees the allocated memory.

     sysctlmif_leaves() and sysctlmif_leavesbyname() allocate memory for a
     list of objects, if id / idlevel or name is a leaf the list contains only
     it, otherwise the list of its descendant leaves; sysctlmif_freelist()
     frees the allocated memory.

     sysctlmif_tree() and sysctlmif_treebyname() allocate memory for a tree of
     sysctlmif_object and returns a pointer to the root, id / idlevel or name
     denote the root, object.children is set and iterable by SLIST macros,
     sysctlmif_freetree() frees the allocated memory.

     sysctlmif_mib() allocates memory for a collection of trees and returns a
     list where the entries are the roots representing the top-level objects,
     sysctlmif_freemib() frees the allocated memory.

   Capability Mode
     In "capability mode", see cap_enter(2), sysctlmibinfo2 checks if the
     object has CTLFLAG_CAPRD or CTLFLAG_CAPWR before to return its info,
     sysctlmif_nextnode(), sysctlmif_nextnodebyname(), sysctlmif_nextleaf()
     and sysctlmif_nextleafbyname() ignore capability flags to traverse the
     tree also in capability mode; properly sysctlmibinfo2 provides
     "capability mode" via sysctlinfo(4) interface.

     The sysctlmif_oidbyname(), sysctlmif_oidextendedbyname(),
     sysctlmif_name(), sysctlmif_desc(), sysctlmif_descbyname(),
     sysctlmif_label(), sysctlmif_labelbyname(), sysctlmif_fmt(),
     sysctlmif_fmtbyname(), sysctlmif_hashandler(),
     sysctlmif_hashandlerbyname(), sysctlmif_kind(), sysctlmif_kindbyname(),
     sysctlmif_nextnode(), sysctlmif_nextnodebyname(), sysctlmif_nextleaf(),
     and sysctlmif_nextleafbyname() functions return the value 0 if
     successful; otherwise the value -1 is returned and the global variable
     errno is set to indicate the error.

     The sysctlmif_object(), sysctlmif_objectbyname(), sysctlmif_list(),
     sysctlmif_grouplist(), sysctlmif_grouplistbyname(), sysctlmif_leaves(),
     sysctlmif_leavesbyname(), sysctlmif_tree(), sysctlmif_treebyname(),
     sysctlmif_mib() functions return NULL upon error or a pointer to
     allocated memory for success.

     Complete set of examples:

     If installed:

     Example to print the Sound Driver objects:

           struct sysctlmif_list *list;
           struct sysctlmif_object *obj;

           if ((list = sysctlmif_leavesbyname("hw.snd")) == NULL)
                   return (1);

           SLIST_FOREACH(obj, list, object_link) {
                   printf("name:   %s\n", obj->name);
                   printf("descr.: %s\n", obj->desc);
                   printf("label:  %s\n", obj->label);
                   printf("flags:  %u\n", obj->flags);
                   printf("type:   %u\n", obj->type);
                   printf("fmt:    %s\n", obj->fmt);


     The following errors may be reported:

     [ECAPMODE]         The node has not the CTLFLAG_CAPRD or CTLFLAG_CAPWR
                        flag in capability mode.

     [EINVAL]           name has more than CTL_MAXNAME levels.

     [EINVAL]           idlevel is either greater CTL_MAXNAME, equal to zero
                        or is not an integer.

     [ENAMETOOLONG]     name is >= MAXPATHLEN.

     [ENOATTR]          The node exists but its info is NULL.

     [ENOENT]           The node does not exist.

     [ENOMEM]           Cannot allocate memory.

     cap_enter(2), queue(3), sysctl(3), sysctlinfo(3), sysctlinfo(4)

     The sysctlmibinfo2 library first appeared in FreeBSD 13.0.

     sysctlmibinfo2 was written by Alfonso Sabato Siciliano

FreeBSD 13.0-ALPHA1            February 26, 2021           FreeBSD 13.0-ALPHA1