2 .\" Copyright (c) 2000, Andrzej Bialecki <abial@FreeBSD.org>
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28 .\" $FreeBSD: src/share/man/man9/sysctl_ctx_init.9,v 1.2.2.6 2001/12/17 11:30:19 ru Exp $
36 .Nm sysctl_ctx_entry_add ,
37 .Nm sysctl_ctx_entry_find ,
38 .Nm sysctl_ctx_entry_del
39 .Nd "sysctl context for managing dynamically created sysctl oids"
44 .Fa "struct sysctl_ctx_list *clist"
48 .Fa "struct sysctl_ctx_list *clist"
50 .Ft struct sysctl_ctx_entry *
51 .Fo sysctl_ctx_entry_add
52 .Fa "struct sysctl_ctx_list *clist"
53 .Fa "struct sysctl_oid *oidp"
55 .Ft struct sysctl_ctx_entry *
56 .Fo sysctl_ctx_entry_find
57 .Fa "struct sysctl_ctx_list *clist"
58 .Fa "struct sysctl_oid *oidp"
61 .Fo sysctl_ctx_entry_del
62 .Fa "struct sysctl_ctx_list *clist"
63 .Fa "struct sysctl_oid *oidp"
66 These functions provide an interface
67 for managing dynamically created oids.
68 The sysctl context is responsible for keeping track of created oids,
69 as well as their proper removal when needed.
70 It adds a simple transactional aspect to oid removal operations;
71 i.e. if a removal operation fails part way,
72 it is possible to roll back the sysctl tree
73 to its previous state.
77 function initializes a sysctl context.
80 argument must point to an already allocated variable.
83 be initialized before use.
84 Once it is initialized,
85 a pointer to the context can be passed as an argument to all the
88 .Xr sysctl_add_oid 9 ) ,
89 and it will be updated with entries pointing to newly created oids.
91 Internally, the context is represented as a
95 .Li struct sysctl_ctx_entry
97 .Bd -literal -offset indent
98 struct sysctl_ctx_entry {
99 struct sysctl_oid *entry;
100 TAILQ_ENTRY(sysctl_ctx_entry) link;
103 TAILQ_HEAD(sysctl_ctx_list, sysctl_ctx_entry);
106 Each context entry points to one dynamic oid that it manages.
107 Newly created oids are always inserted in the front of the list.
111 function removes the context and associated oids it manages.
112 If the function completes successfuly,
113 all managed oids have been unregistered
114 (removed from the tree)
116 together with all their allocated memory,
117 and the entries of the context have been freed as well.
119 The removal operation is performed in two steps.
120 First, for each context entry, the function
121 .Xr sysctl_remove_oid 9
122 is executed, with parameter
124 set to 0, which inhibits the freeing of resources.
125 If there are no errors during this step,
127 proceeds to the next step.
128 If the first step fails,
129 all unregistered oids associated with the context are registered again.
132 in most cases, the programmer specifies
134 as the oid number when creating an oid.
135 However, during registration of the oid in the tree,
136 this number is changed to the first available number
138 If the first step of context deletion fails,
139 re-registration of the oid does not change the already assigned oid number
140 (which is different from OID_AUTO).
141 This ensures that re-registered entries
142 maintain their original positions in the tree.
144 The second step actually performs the deletion of the dynamic oids.
145 .Xr sysctl_remove_oid 9
146 iterates through the context list,
147 starting from beginning (i.e. the newest entries).
149 this time, the function not only deletes the oids from the tree,
150 but also frees their memory (provided that oid_refcnt == 0),
151 as well as the memory of all context entries.
154 .Fn sysctl_ctx_entry_add
155 function allows the addition of an existing dynamic oid to a context.
158 .Fn sysctl_ctx_entry_del
159 function removes an entry from the context.
161 in this case, only the corresponding
162 .Li struct sysctl_ctx_entry
165 pointer remains intact.
166 Thereafter, the programmer is responsible for managing the resources
167 allocated to this oid.
170 .Fn sysctl_ctx_entry_find
171 function searches for a given
173 witin a context list,
174 either returning a pointer to the
175 .Fa struct sysctl_ctx_entry
180 The following is an example of how to create a new top-level category
181 and how to hook up another subtree to an existing static node.
182 This example uses contexts to keep track of the oids.
184 #include <sys/sysctl.h>
186 struct sysctl_ctx_list clist;
187 struct sysctl_oid *oidp;
189 char *string = "dynamic sysctl";
192 sysctl_ctx_init(&clist);
193 oidp = SYSCTL_ADD_NODE( &clist, SYSCTL_STATIC_CHILDREN(/* tree top */),
194 OID_AUTO, newtree, CTFLAG_RW, 0, "new top level tree");
195 oidp = SYSCTL_ADD_INT( &clist, SYSCTL_CHILDREN(oidp),
196 OID_AUTO, newint, CTLFLAG_RW, &a_int, 0, "new int leaf");
198 oidp = SYSCTL_ADD_NODE( &clist, SYSCTL_STATIC_CHILDREN(_debug),
199 OID_AUTO, newtree, CTFLAG_RW, 0, "new tree under debug");
200 oidp = SYSCTL_ADD_STRING( &clist, SYSCTL_CHILDREN(oidp),
201 OID_AUTO, newstring, CTLFLAG_R, string, 0, "new string leaf");
203 /* Now we can free up the oids */
204 if(sysctl_ctx_free(&clist)) {
205 printf("can't free this context - other oids depend on it");
208 printf("Success!\\n"):
213 This example creates the following subtrees:
214 .Bd -literal -offset indent
215 debug.newtree.newstring
219 Note that both trees are removed, and their resources freed,
222 call, which starts by freeing the newest entries (leaves)
223 and then proceeds to free the older entries (in this case the nodes).
227 .Xr sysctl_add_oid 9 ,
228 .Xr sysctl_remove_oid 9
230 These functions first appeared in
233 .An Andrzej Bialecki Aq abial@FreeBSD.org
235 The current removal algorithm is somewhat heavy.
237 all oids need to be unregistered, registered again,
238 and then unregistered and deleted.
239 However, the algorithm does guarantee transactional properties
240 for removal operations.
242 All operations on contexts involve linked list traversal.
244 creation and removal of entries is relatively costly.