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NAME

     sysctl_add_oid, sysctl_move_oid, sysctl_remove_oid - runtime sysctl tree
     manipulation

SYNOPSIS

     #include <sys/types.h>
     #include <sys/sysctl.h>

     struct sysctl_oid *
     sysctl_add_oid(struct sysctl_ctx_list *ctx,
             struct sysctl_oid_list *parent, int number, const char *name,
             int kind, void *arg1, int arg2,
             int (*handler) (SYSCTL_HANDLER_ARGS), const char *format,
             const char *descr);

     int
     sysctl_move_oid(struct sysctl_oid *oidp, struct sysctl_oid_list *parent);

     int
     sysctl_remove_oid(struct sysctl_oid *oidp, int del, int recurse);

     struct sysctl_oid_list *
     SYSCTL_CHILDREN(struct sysctl_oid *oidp);

     struct sysctl_oid_list *
     SYSCTL_STATIC_CHILDREN(struct sysctl_oid_list OID_NAME);

     struct sysctl_oid *
     SYSCTL_ADD_OID(struct sysctl_ctx_list *ctx,
             struct sysctl_oid_list *parent, int number, const char *name,
             int kind, void *arg1, int arg2,
             int (*handler) (SYSCTL_HANDLER_ARGS), const char *format,
             const char *descr);

     struct sysctl_oid *
     SYSCTL_ADD_NODE(struct sysctl_ctx_list *ctx,
             struct sysctl_oid_list *parent, int number, const char *name,
             int access, int (*handler) (SYSCTL_HANDLER_ARGS),
             const char *descr);

     struct sysctl_oid *
     SYSCTL_ADD_STRING(struct sysctl_ctx_list *ctx,
             struct sysctl_oid_list *parent, int number, const char *name,
             int access, char *arg, int len, const char *descr);

     struct sysctl_oid *
     SYSCTL_ADD_INT(struct sysctl_ctx_list *ctx,
             struct sysctl_oid_list *parent, int number, const char *name,
             int access, int *arg, int len, const char *descr);

     struct sysctl_oid *
     SYSCTL_ADD_UINT(struct sysctl_ctx_list *ctx,
             struct sysctl_oid_list *parent, int number, const char *name,
             int access, unsigned int *arg, int len, const char *descr);

     struct sysctl_oid *
     SYSCTL_ADD_LONG(struct sysctl_ctx_list *ctx,
             struct sysctl_oid_list *parent, int number, const char *name,
             int access, long *arg, const char *descr);

     struct sysctl_oid *
     SYSCTL_ADD_ULONG(struct sysctl_ctx_list *ctx,
             struct sysctl_oid_list *parent, int number, const char *name,
             int access, unsigned long *arg, const char *descr);

     struct sysctl_oid *
     SYSCTL_ADD_OPAQUE(struct sysctl_ctx_list *ctx,
             struct sysctl_oid_list *parent, int number, const char *name,
             int access, void *arg, int len, const char *format,
             const char *descr);

     struct sysctl_oid *
     SYSCTL_ADD_STRUCT(struct sysctl_ctx_list *ctx,
             struct sysctl_oid_list *parent, int number, const char *name,
             int access, void *arg, STRUCT_NAME, const char *descr);

     struct sysctl_oid *
     SYSCTL_ADD_PROC(struct sysctl_ctx_list *ctx,
             struct sysctl_oid_list *parent, int number, const char *name,
             int access, void *arg1, int arg2,
             int (*handler) (SYSCTL_HANDLER_ARGS), const char *format,
             const char *descr);

DESCRIPTION

     These functions and macros provide an interface for creating and deleting
     sysctl oids at runtime (e.g. during lifetime of a module).  The
     alternative method, based on linker sets (see #include <sys/linker_set.h>
     and src/sys/kern/kern_sysctl.c for details), only allows creation and
     deletion on module load and unload respectively.

     Dynamic oids of type CTLTYPE_NODE are reusable so that several code
     sections can create and delete them, but in reality they are allocated
     and freed based on their reference count.  As a consequence, it is
     possible for two or more code sections to create partially overlapping
     trees that they both can use.  It is not possible to create overlapping
     leaves, nor to create different child types with the same name and
     parent.

     Newly created oids are connected to their parent nodes.  In all these
     functions and macros (with the exception of sysctl_remove_oid()), one of
     the required parameters is parent, which points to the head of the
     parent’s list of children.

     Most top level categories are created statically.  When connecting to
     existing static oids, this pointer can be obtained with the
     SYSCTL_STATIC_CHILDREN() macro, where the OID_NAME argument is name of
     the parent oid of type CTLTYPE_NODE (i.e., the name displayed by
     sysctl(8), preceded by underscore, and with all dots replaced with
     underscores).

     When connecting to an existing dynamic oid, this pointer can be obtained
     with the SYSCTL_CHILDREN() macro, where the oidp argument points to the
     parent oid of type CTLTYPE_NODE.

     The sysctl_add_oid() function creates raw oids of any type.  If the oid
     is successfully created, the function returns a pointer to it; otherwise
     it returns NULL.  Many of the arguments for sysctl_add_oid() are common
     to the macros.  The arguments are as follows:

     ctx      A pointer to an optional sysctl context, or NULL.  See
              sysctl_ctx_init(9) for details.  Programmers are strongly
              advised to use contexts to organize the dynamic oids which they
              create, unless special creation and deletion sequences are
              required.  If ctx is not NULL, the newly created oid will be
              added to this context as its first entry.

     parent   A pointer to a struct sysctl_oid_list, which is the head of the
              parent’s list of children.

     number   The oid number that will be assigned to this oid.  In almost all
              cases this should be set to OID_AUTO, which will result in the
              assignment of the next available oid number.

     name     The name of the oid.  The newly created oid will contain a copy
              of the name.

     kind     The kind of oid, specified as a bit mask of the type and access
              values defined in the #include <sys/sysctl.h>
              header file.  Oids created dynamically always have the
              CTLFLAG_DYN flag set.  Access flags specify whether this oid is
              read-only or read-write, and whether it may be modified by all
              users or by the superuser only.

     arg1     A pointer to any data that the oid should reference, or NULL.

     arg2     The size of arg1, or 0 if arg1 is NULL.

     handler  A pointer to the function that is responsible for handling read
              and write requests to this oid.  There are several standard
              handlers that support operations on nodes, integers, strings and
              opaque objects.  It is possible also to define new handlers
              using the SYSCTL_ADD_PROC() macro.

     format   A pointer to a string which specifies the format of the oid
              symbolically.  This format is used as a hint by sysctl(8) to
              apply proper data formatting for display purposes.  Currently
              used format names are: “N” for node, “A” for char *, “I” for
              int, “IU” for unsigned int, “L” for long, “LU” for unsigned long
              and “S,TYPE” for struct TYPE structures.

     descr    A pointer to a textual description of the oid.

     The sysctl_move_oid() function reparents an existing oid.  The oid is
     assigned a new number as if it had been created with number set to
     OID_AUTO.

     The sysctl_remove_oid() function removes a dynamically created oid from
     the tree, optionally freeing its resources.  It takes the following
     arguments:

     oidp     A pointer to the dynamic oid to be removed.  If the oid is not
              dynamic, or the pointer is NULL, the function returns EINVAL.

     del      If non-zero, sysctl_remove_oid() will try to free the oid’s
              resources when the reference count of the oid becomes zero.
              However, if del is set to 0, the routine will only deregister
              the oid from the tree, without freeing its resources.  This
              behaviour is useful when the caller expects to rollback
              (possibly partially failed) deletion of many oids later.

     recurse  If non-zero, attempt to remove the node and all its children.
              If recurse is set to 0, any attempt to remove a node that
              contains any children will result in a ENOTEMPTY error.
              WARNING: use recursive deletion with extreme caution!  Normally
              it should not be needed if contexts are used.  Contexts take
              care of tracking inter-dependencies between users of the tree.
              However, in some extreme cases it might be necessary to remove
              part of the subtree no matter how it was created, in order to
              free some other resources.  Be aware, though, that this may
              result in a system panic(9) if other code sections continue to
              use removed subtrees.

     Again, in most cases the programmer should use contexts, as described in
     sysctl_ctx_init(9), to keep track of created oids, and to delete them
     later in orderly fashion.

     There is a set of macros defined that helps to create oids of given type.
     They are as follows:

     SYSCTL_ADD_OID()     creates a raw oid.  This macro is functionally
                          equivalent to the sysctl_add_oid() function.

     SYSCTL_ADD_NODE()    creates an oid of type CTLTYPE_NODE, to which child
                          oids may be added.

     SYSCTL_ADD_STRING()  creates an oid that handles a zero-terminated
                          character string.

     SYSCTL_ADD_INT()     creates an oid that handles an int variable.

     SYSCTL_ADD_UINT()    creates an oid that handles an unsigned int
                          variable.

     SYSCTL_ADD_LONG()    creates an oid that handles a long variable.

     SYSCTL_ADD_ULONG()   creates an oid that handles an unsigned long
                          variable.

     SYSCTL_ADD_OPAQUE()  creates an oid that handles any chunk of opaque data
                          of the size specified by the len argument, which is
                          a pointer to a size_t *.

     SYSCTL_ADD_STRUCT()  creates an oid that handles a struct TYPE structure.
                          The format parameter will be set to “S,TYPE” to
                          provide proper hints to the sysctl(8) utility.

     SYSCTL_ADD_PROC()    creates an oid with the specified handler function.
                          The handler is responsible for handling read and
                          write requests to the oid.  This oid type is
                          especially useful if the kernel data is not easily
                          accessible, or needs to be processed before
                          exporting.

EXAMPLES

     The following is an example of how to create a new top-level category and
     how to hook up another subtree to an existing static node.  This example
     does not use contexts, which results in tedious management of all
     intermediate oids, as they need to be freed later on:

     #include <sys/sysctl.h>
      ...
     /* Need to preserve pointers to newly created subtrees, to be able
      * to free them later.
      */
     struct sysctl_oid *root1, *root2, *oidp;
     int a_int;
     char *string = "dynamic sysctl";
      ...

     root1 = SYSCTL_ADD_NODE( NULL, SYSCTL_STATIC_CHILDREN(/* tree top */),
             OID_AUTO, "newtree", CTLFLAG_RW, 0, "new top level tree");
     oidp = SYSCTL_ADD_INT( NULL, SYSCTL_CHILDREN(root1),
             OID_AUTO, "newint", CTLFLAG_RW, &a_int, 0, "new int leaf");
      ...
     root2 = SYSCTL_ADD_NODE( NULL, SYSCTL_STATIC_CHILDREN(_debug),
             OID_AUTO, "newtree", CTLFLAG_RW, 0, "new tree under debug");
     oidp = SYSCTL_ADD_STRING( NULL, SYSCTL_CHILDREN(root2),
             OID_AUTO, "newstring", CTLFLAG_RD, string, 0, "new string leaf");

     This example creates the following subtrees:

           debug.newtree.newstring
           newtree.newint

     Care should be taken to free all oids once they are no longer needed!

SEE ALSO

     sysctl(8), sysctl(9), sysctl_ctx_free(9), sysctl_ctx_init(9)

HISTORY

     These functions first appeared in FreeBSD 4.2.

AUTHORS

     Andrzej Bialecki 〈abial@FreeBSD.org

BUGS

     Sharing nodes between many code sections causes interdependencies that
     sometimes may lock the resources.  For example, if module A hooks up a
     subtree to an oid created by module B, module B will be unable to delete
     that oid.  These issues are handled properly by sysctl contexts.

     Many operations on the tree involve traversing linked lists.  For this
     reason, oid creation and removal is relatively costly.