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<table class="head">
<tr>
<td class="head-ltitle">SYSCTL_ADD_OID(9)</td>
<td class="head-vol">Kernel Developer's Manual</td>
<td class="head-rtitle">SYSCTL_ADD_OID(9)</td>
</tr>
</table>
<div class="manual-text">
<section class="Sh">
<h1 class="Sh" id="NAME"><a class="permalink" href="#NAME">NAME</a></h1>
<p class="Pp"><code class="Nm">sysctl_add_oid</code>,
<code class="Nm">sysctl_move_oid</code>,
<code class="Nm">sysctl_remove_oid</code>,
<code class="Nm">sysctl_remove_name</code> — <span class="Nd">runtime
sysctl tree manipulation</span></p>
</section>
<section class="Sh">
<h1 class="Sh" id="SYNOPSIS"><a class="permalink" href="#SYNOPSIS">SYNOPSIS</a></h1>
<p class="Pp"><code class="In">#include
<<a class="In">sys/types.h</a>></code>
<br/>
<code class="In">#include <<a class="In">sys/sysctl.h</a>></code></p>
<p class="Pp"><var class="Ft">struct sysctl_oid *</var>
<br/>
<code class="Fn">sysctl_add_oid</code>(<var class="Fa">struct sysctl_ctx_list
*ctx</var>, <var class="Fa">struct sysctl_oid_list *parent</var>,
<var class="Fa">int number</var>, <var class="Fa">const char *name</var>,
<var class="Fa">int kind</var>, <var class="Fa">void *arg1</var>,
<var class="Fa">intmax_t arg2</var>, <var class="Fa">int (*handler)
(SYSCTL_HANDLER_ARGS)</var>, <var class="Fa">const char *format</var>,
<var class="Fa">const char *descr</var>, <var class="Fa">const char
*label</var>);</p>
<p class="Pp"><var class="Ft">int</var>
<br/>
<code class="Fn">sysctl_move_oid</code>(<var class="Fa">struct sysctl_oid
*oidp</var>, <var class="Fa">struct sysctl_oid_list *parent</var>);</p>
<p class="Pp"><var class="Ft">int</var>
<br/>
<code class="Fn">sysctl_remove_oid</code>(<var class="Fa">struct sysctl_oid
*oidp</var>, <var class="Fa">int del</var>, <var class="Fa">int
recurse</var>);</p>
<p class="Pp"><var class="Ft">int</var>
<br/>
<code class="Fn">sysctl_remove_name</code>(<var class="Fa">struct sysctl_oid
*oidp</var>, <var class="Fa">const char *name</var>, <var class="Fa">int
del</var>, <var class="Fa">int recurse</var>);</p>
</section>
<section class="Sh">
<h1 class="Sh" id="DESCRIPTION"><a class="permalink" href="#DESCRIPTION">DESCRIPTION</a></h1>
<p class="Pp">These functions provide the interface for creating and deleting
sysctl OIDs at runtime for example during the lifetime of a module. The
wrapper macros defined by <a class="Xr">sysctl(9)</a> are recommended when
creating new OIDs.
<a class="permalink" href="#sysctl_add_oid"><code class="Fn" id="sysctl_add_oid">sysctl_add_oid</code></a>()
should not be called directly from the code.</p>
<p class="Pp">Dynamic OIDs of type <code class="Dv">CTLTYPE_NODE</code> 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.</p>
<p class="Pp" id="sysctl_add_oid~2">The
<a class="permalink" href="#sysctl_add_oid~2"><code class="Fn">sysctl_add_oid</code></a>()
function creates a raw OID of any type and connects it to its parent node,
if any. If the OID is successfully created, the function returns a pointer
to it else it returns <code class="Dv">NULL</code>. Many of the arguments
for <code class="Fn">sysctl_add_oid</code>() are common to the wrapper
macros defined by <a class="Xr">sysctl(9)</a>.</p>
<p class="Pp" id="sysctl_move_oid">The
<a class="permalink" href="#sysctl_move_oid"><code class="Fn">sysctl_move_oid</code></a>()
function reparents an existing OID. The OID is assigned a new number as if
it had been created with <var class="Fa">number</var> set to
<code class="Dv">OID_AUTO</code>.</p>
<p class="Pp" id="sysctl_remove_oid">The
<a class="permalink" href="#sysctl_remove_oid"><code class="Fn">sysctl_remove_oid</code></a>()
function removes a dynamically created OID from the tree and optionally
freeing its resources. It takes the following arguments:</p>
<dl class="Bl-tag">
<dt><var class="Fa">oidp</var></dt>
<dd>A pointer to the dynamic OID to be removed. If the OID is not dynamic, or
the pointer is <code class="Dv">NULL</code>, the function returns
<code class="Er">EINVAL</code>.</dd>
<dt><var class="Fa">del</var></dt>
<dd>If non-zero, <code class="Fn">sysctl_remove_oid</code>() will try to free
the OID's resources when the reference count of the OID becomes zero.
However, if <var class="Fa">del</var> 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.</dd>
<dt id="WARNING"><var class="Fa">recurse</var></dt>
<dd>If non-zero, attempt to remove the node and all its children. If
<span class="Pa">recurse</span> is set to 0, any attempt to remove a node
that contains any children will result in a
<code class="Er">ENOTEMPTY</code> error.
<a class="permalink" href="#WARNING"><i class="Em">WARNING</i></a>:
<a class="permalink" href="#use"><i class="Em" id="use">use recursive
deletion with extreme caution</i></a>! 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 <a class="Xr">panic(9)</a> if other code sections continue to
use removed subtrees.</dd>
</dl>
<p class="Pp" id="sysctl_remove_name">The
<a class="permalink" href="#sysctl_remove_name"><code class="Fn">sysctl_remove_name</code></a>()
function looks up the child node matching the <var class="Fa">name</var>
argument and then invokes the <code class="Fn">sysctl_remove_oid</code>()
function on that node, passing along the <var class="Fa">del</var> and
<var class="Fa">recurse</var> arguments. If a node having the specified name
does not exist an error code of <code class="Er">ENOENT</code> is returned.
Else the error code from <code class="Fn">sysctl_remove_oid</code>() is
returned.</p>
<p class="Pp">In most cases the programmer should use contexts, as described in
<a class="Xr">sysctl_ctx_init(9)</a>, to keep track of created OIDs, and to
delete them later in orderly fashion.</p>
</section>
<section class="Sh">
<h1 class="Sh" id="SEE_ALSO"><a class="permalink" href="#SEE_ALSO">SEE
ALSO</a></h1>
<p class="Pp"><a class="Xr">sysctl(8)</a>, <a class="Xr">sysctl(9)</a>,
<a class="Xr">sysctl_ctx_free(9)</a>,
<a class="Xr">sysctl_ctx_init(9)</a></p>
</section>
<section class="Sh">
<h1 class="Sh" id="HISTORY"><a class="permalink" href="#HISTORY">HISTORY</a></h1>
<p class="Pp">These functions first appeared in <span class="Ux">FreeBSD
4.2</span>.</p>
</section>
<section class="Sh">
<h1 class="Sh" id="AUTHORS"><a class="permalink" href="#AUTHORS">AUTHORS</a></h1>
<p class="Pp"><span class="An">Andrzej Bialecki</span>
<<a class="Mt" href="mailto:abial@FreeBSD.org">abial@FreeBSD.org</a>></p>
</section>
<section class="Sh">
<h1 class="Sh" id="BUGS"><a class="permalink" href="#BUGS">BUGS</a></h1>
<p class="Pp">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.</p>
<p class="Pp">Many operations on the tree involve traversing linked lists. For
this reason, OID creation and removal is relatively costly.</p>
</section>
</div>
<table class="foot">
<tr>
<td class="foot-date">December 13, 2016</td>
<td class="foot-os">FreeBSD 15.0</td>
</tr>
</table>
|
