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

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 alterna-
     tive method, based	on linker sets (see <sys/linker_set.h> and
     src/sys/kern/kern_sysctl.c	for details), only allows creation and dele-
     tion on module load and unload respectively.

     Dynamic oids of type CTLTYPE_NODE are reusable so that several code sec-
     tions 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	par-
     ent'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	under-
     scores).

     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 <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 han-
	      dlers 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 sym-
	      bolically.  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 argu-
     ments:

     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 be-
	      haviour 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	con-
	      tains 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	char-
			  acter	string.

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

     SYSCTL_ADD_UINT()	  creates an oid that handles an unsigned int vari-
			  able.

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

     SYSCTL_ADD_ULONG()	  creates an oid that handles an unsigned long vari-
			  able.

     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 espe-
			  cially useful	if the kernel data is not easily
			  accessible, or needs to be processed before export-
			  ing.

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 inter-
     mediate 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.

FreeBSD	9.2			 July 15, 2000			   FreeBSD 9.2

NAME | SYNOPSIS | DESCRIPTION | EXAMPLES | SEE ALSO | HISTORY | AUTHORS | BUGS

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