642 lines
18 KiB
Groff
642 lines
18 KiB
Groff
.\" $NetBSD: sysctl.9,v 1.12 2008/08/15 21:10:14 wiz Exp $
|
|
.\"
|
|
.\" Copyright (c) 2004 The NetBSD Foundation, Inc.
|
|
.\" All rights reserved.
|
|
.\"
|
|
.\" This code is derived from software contributed to The NetBSD Foundation
|
|
.\" by Andrew Brown.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
|
|
.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
|
|
.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
|
|
.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
|
|
.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
|
|
.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
|
|
.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
|
|
.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
|
|
.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
|
|
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
|
|
.\" POSSIBILITY OF SUCH DAMAGE.
|
|
.\"
|
|
.Dd August 15, 2008
|
|
.Dt SYSCTL 9
|
|
.Os
|
|
.Sh NAME
|
|
.Nm sysctl
|
|
.Nd system variable control interfaces
|
|
.Sh SYNOPSIS
|
|
.In sys/param.h
|
|
.In sys/sysctl.h
|
|
.Pp
|
|
Primary external interfaces:
|
|
.Ft void
|
|
.Fn sysctl_init void
|
|
.Ft int
|
|
.Fn sysctl_lock "struct lwp *l" "void *oldp" "size_t savelen"
|
|
.Ft int
|
|
.Fn sysctl_dispatch "const int *name" "u_int namelen" "void *oldp" \
|
|
"size_t *oldlenp" "const void *newp" "size_t newlen" "const int *oname" \
|
|
"struct lwp *l" "const struct sysctlnode *rnode"
|
|
.Ft void
|
|
.Fn sysctl_unlock "struct lwp *l"
|
|
.Ft int
|
|
.Fn sysctl_createv "struct sysctllog **log" "int cflags" \
|
|
"const struct sysctlnode **rnode" "const struct sysctlnode **cnode" \
|
|
"int flags" "int type" "const char *namep" "const char *desc" \
|
|
"sysctlfn func" "u_quad_t qv" "void *newp" "size_t newlen" ...
|
|
.Ft int
|
|
.Fn sysctl_destroyv "struct sysctlnode *rnode" ...
|
|
.Ft void
|
|
.Fn sysctl_free "struct sysctlnode *rnode"
|
|
.Ft void
|
|
.Fn sysctl_teardown "struct sysctllog **"
|
|
.Ft int
|
|
.Fn old_sysctl "int *name" "u_int namelen" "void *oldp" \
|
|
"size_t *oldlenp" "void *newp" "size_t newlen" "struct lwp *l"
|
|
.Pp
|
|
Core internal functions:
|
|
.Ft int
|
|
.Fn sysctl_locate "struct lwp *l" "const int *name" "u_int namelen" \
|
|
"const struct sysctlnode **rnode" "int *nip"
|
|
.Ft int
|
|
.Fn sysctl_lookup "const int *name" "u_int namelen" "void *oldp" \
|
|
"size_t *oldlenp" "const void *newp" "size_t newlen" "const int *oname" \
|
|
"struct lwp *l" "const struct sysctlnode *rnode"
|
|
.Ft int
|
|
.Fn sysctl_create "const int *name" "u_int namelen" "void *oldp" \
|
|
"size_t *oldlenp" "const void *newp" "size_t newlen" "const int *oname" \
|
|
"struct lwp *l" "const struct sysctlnode *rnode"
|
|
.Ft int
|
|
.Fn sysctl_destroy "const int *name" "u_int namelen" "void *oldp" \
|
|
"size_t *oldlenp" "const void *newp" "size_t newlen" "const int *oname" \
|
|
"struct lwp *l" "const struct sysctlnode *rnode"
|
|
.Ft int
|
|
.Fn sysctl_query "const int *name" "u_int namelen" "void *oldp" \
|
|
"size_t *oldlenp" "const void *newp" "size_t newlen" "const int *oname" \
|
|
"struct lwp *l" "const struct sysctlnode *rnode"
|
|
.Pp
|
|
Simple
|
|
.Dq helper
|
|
functions:
|
|
.Ft int
|
|
.Fn sysctl_needfunc "const int *name" "u_int namelen" "void *oldp" \
|
|
"size_t *oldlenp" "const void *newp" "size_t newlen" "const int *oname" \
|
|
"struct lwp *l" "const struct sysctlnode *rnode"
|
|
.Ft int
|
|
.Fn sysctl_notavail "const int *name" "u_int namelen" "void *oldp" \
|
|
"size_t *oldlenp" "const void *newp" "size_t newlen" "const int *oname" \
|
|
"struct lwp *l" "const struct sysctlnode *rnode"
|
|
.Ft int
|
|
.Fn sysctl_null "const int *name" "u_int namelen" "void *oldp" \
|
|
"size_t *oldlenp" "const void *newp" "size_t newlen" "const int *oname" \
|
|
"struct lwp *l" "const struct sysctlnode *rnode"
|
|
.Sh DESCRIPTION
|
|
The SYSCTL subsystem instruments a number of kernel tunables and other
|
|
data structures via a simple MIB-like interface, primarily for
|
|
consumption by userland programs, but also for use internally by the
|
|
kernel.
|
|
.Sh LOCKING
|
|
All operations on the SYSCTL tree must be protected by acquiring the
|
|
main SYSCTL lock.
|
|
The only functions that can be called when the lock is not held are
|
|
.Fn sysctl_lock ,
|
|
.Fn sysctl_createv ,
|
|
.Fn sysctl_destroyv ,
|
|
and
|
|
.Fn old_sysctl .
|
|
All other functions require the tree to be locked.
|
|
This is to prevent other users of the tree from moving nodes around
|
|
during an add operation, or from destroying nodes or subtrees that are
|
|
actively being used.
|
|
The lock is acquired by calling
|
|
.Fn sysctl_lock
|
|
with a pointer to the process's lwp
|
|
.Fa l
|
|
.Dv ( NULL
|
|
may be passed to all functions as the lwp pointer if no lwp is
|
|
appropriate, though any changes made via
|
|
.Fn sysctl_create ,
|
|
.Fn sysctl_destroy ,
|
|
.Fn sysctl_lookup ,
|
|
or by any helper function will be done with effective superuser
|
|
privileges).
|
|
The
|
|
.Fa oldp
|
|
and
|
|
.Fa savelen
|
|
arguments are a pointer to and the size of the memory region the
|
|
caller will be using to collect data from SYSCTL.
|
|
These may also be
|
|
.Dv NULL
|
|
and 0, respectively.
|
|
.Pp
|
|
The memory region will be locked via
|
|
.Fn uvm_vslock
|
|
if it is a region in userspace.
|
|
The address and size of the region are recorded so that when the
|
|
SYSCTL lock is to be released via
|
|
.Fn sysctl_unlock ,
|
|
only the lwp pointer
|
|
.Fa l
|
|
is required.
|
|
.Sh LOOKUPS
|
|
Once the lock has been acquired, it is typical to call
|
|
.Fn sysctl_dispatch
|
|
to handle the request.
|
|
.Fn sysctl_dispatch
|
|
will examine the contents of
|
|
.Fa name ,
|
|
an array of integers at least
|
|
.Fa namelen
|
|
long, which is to be located in kernel space, in order to determine
|
|
which function to call to handle the specific request.
|
|
.Pp
|
|
.Fn sysctl_dispatch
|
|
uses the following algorithm to determine the function to call:
|
|
.Pp
|
|
.Bl -bullet
|
|
.It
|
|
Scan the tree using
|
|
.Fn sysctl_locate
|
|
.It
|
|
If the node returned has a
|
|
.Dq helper
|
|
function, call it
|
|
.It
|
|
If the requested node was found but has no function, call
|
|
.Fn sysctl_lookup
|
|
.It
|
|
If the node was not found and
|
|
.Fa name
|
|
specifies one of
|
|
.Fn sysctl_query ,
|
|
.Fn sysctl_create ,
|
|
or
|
|
.Fn sysctl_destroy ,
|
|
call the appropriate function
|
|
.It
|
|
If none of these options applies and no other error was yet recorded,
|
|
return
|
|
.Er EOPNOTSUPP
|
|
.Pp
|
|
.El
|
|
The
|
|
.Fa oldp
|
|
and
|
|
.Fa oldlenp
|
|
arguments to
|
|
.Fn sysctl_dispatch ,
|
|
as with all the other core functions, describe an area into which the
|
|
current or requested value may be copied.
|
|
.Fa oldp
|
|
may or may not be a pointer into userspace (as dictated by whether
|
|
.Fa l
|
|
is
|
|
.Dv NULL
|
|
or not).
|
|
.Fa oldlenp
|
|
is a
|
|
.No non- Ns Dv NULL
|
|
pointer to a size_t.
|
|
.Fa newp
|
|
and
|
|
.Fa newlen
|
|
describe an area where the new value for the request may be found;
|
|
.Fa newp
|
|
may also be a pointer into userspace.
|
|
The
|
|
.Fa oname
|
|
argument is a
|
|
.No non- Ns Dv NULL
|
|
pointer to the base of the request currently
|
|
being processed.
|
|
By simple arithmetic on
|
|
.Fa name ,
|
|
.Fa namelen ,
|
|
and
|
|
.Fa oname ,
|
|
one can easily determine the entire original request and
|
|
.Fa namelen
|
|
values, if needed.
|
|
The
|
|
.Fa rnode
|
|
value, as passed to
|
|
.Fn sysctl_dispatch
|
|
represents the root of the tree into which the current request is to
|
|
be dispatched.
|
|
If
|
|
.Dv NULL ,
|
|
the main tree will be used.
|
|
.Pp
|
|
.Fn sysctl_locate
|
|
scans a tree for the node most specific to a request.
|
|
If the pointer referenced by
|
|
.Fa rnode
|
|
is not
|
|
.Dv NULL ,
|
|
the tree indicated is searched, otherwise the main tree
|
|
will be used.
|
|
The address of the most relevant node will be returned via
|
|
.Fa rnode
|
|
and the number of MIB entries consumed will be returned via
|
|
.Fa nip ,
|
|
if it is not
|
|
.Dv NULL .
|
|
.Pp
|
|
The
|
|
.Fn sysctl_lookup
|
|
function takes the same arguments as
|
|
.Fn sysctl_dispatch
|
|
with the caveat that the value for
|
|
.Fa namelen
|
|
must be zero in order to indicate that the node referenced by the
|
|
.Fa rnode
|
|
argument is the one to which the lookup is being applied.
|
|
.Sh CREATION AND DESTRUCTION OF NODES
|
|
New nodes are created and destroyed by the
|
|
.Fn sysctl_create
|
|
and
|
|
.Fn sysctl_destroy
|
|
functions.
|
|
These functions take the same arguments as
|
|
.Fn sysctl_dispatch
|
|
with the additional requirement that the
|
|
.Fa namelen
|
|
argument must be 1 and the
|
|
.Fa name
|
|
argument must point to an integer valued either
|
|
.Dv CTL_CREATE
|
|
or
|
|
.Dv CTL_CREATESYM
|
|
when creating a new node, or
|
|
.Dv CTL_DESTROY
|
|
when destroying
|
|
a node.
|
|
The
|
|
.Fa newp
|
|
and
|
|
.Fa newlen
|
|
arguments should point to a copy of the node to be created or
|
|
destroyed.
|
|
If the create or destroy operation was successful, a copy of the node
|
|
created or destroyed will be placed in the space indicated by
|
|
.Fa oldp
|
|
and
|
|
.Fa oldlenp .
|
|
If the create operation fails because of a conflict with an existing
|
|
node, a copy of that node will be returned instead.
|
|
.Pp
|
|
In order to facilitate the creation and destruction of nodes from a
|
|
given tree by kernel subsystems, the functions
|
|
.Fn sysctl_createv
|
|
and
|
|
.Fn sysctl_destroyv
|
|
are provided.
|
|
These functions take care of the overhead of filling in the contents
|
|
of the create or destroy request, dealing with locking, locating the
|
|
appropriate parent node, etc.
|
|
.Pp
|
|
The arguments to
|
|
.Fn sysctl_createv
|
|
are used to construct the new node.
|
|
If the
|
|
.Fa log
|
|
argument is not
|
|
.Dv NULL ,
|
|
a sysctllog structure will be allocated and the pointer referenced
|
|
will be changed to address it.
|
|
The same log may be used for any number of nodes, provided they are
|
|
all inserted into the same tree.
|
|
This allows for a series of nodes to be created and later removed from
|
|
the tree in a single transaction (via
|
|
.Fn sysctl_teardown )
|
|
without the need for any record
|
|
keeping on the caller's part.
|
|
The
|
|
.Fa cflags
|
|
argument is currently unused and must be zero.
|
|
The
|
|
.Fa rnode
|
|
argument must either be
|
|
.Dv NULL
|
|
or a valid pointer to a reference to the root of the tree into which
|
|
the new node must be placed.
|
|
If it is
|
|
.Dv NULL ,
|
|
the main tree will be used.
|
|
It is illegal for
|
|
.Fa rnode
|
|
to refer to a
|
|
.Dv NULL
|
|
pointer.
|
|
If the
|
|
.Fa cnode
|
|
argument is not
|
|
.Dv NULL ,
|
|
on return it will be adjusted to point to the address of the new node.
|
|
.Pp
|
|
The
|
|
.Fa flags
|
|
and
|
|
.Fa type
|
|
arguments are combined into the
|
|
.Fa sysctl_flags
|
|
field, and the current value for
|
|
.Dv SYSCTL_VERSION
|
|
is added in.
|
|
Note: the
|
|
.Dv CTLFLAG_PERMANENT
|
|
flag can only be set from SYSCTL setup routines (see
|
|
.Sx SETUP FUNCTIONS )
|
|
as called by
|
|
.Fn sysctl_init .
|
|
The
|
|
.Fa namep
|
|
argument is copied into the
|
|
.Fa sysctl_name
|
|
field and must be less than
|
|
.Dv SYSCTL_NAMELEN
|
|
characters in length.
|
|
The string indicated by
|
|
.Fa desc
|
|
will be copied if the
|
|
.Dv CTLFLAG_OWNDESC
|
|
flag is set, and will be used as the node's description.
|
|
Note: if
|
|
.Fn sysctl_destroyv
|
|
attempts to delete a node that does not own its own description (and
|
|
is not marked as permanent), but the deletion fails, the description
|
|
will be copied and
|
|
.Fn sysctl_destroyv
|
|
will set the
|
|
.Dv CTLFLAG_OWNDESC
|
|
flag.
|
|
.Pp
|
|
The
|
|
.Fa func
|
|
argument is the name of a
|
|
.Dq helper
|
|
function (see
|
|
.Sx HELPER FUNCTIONS AND MACROS ) .
|
|
If the
|
|
.Dv CTLFLAG_IMMEDIATE
|
|
flag is set, the
|
|
.Fa qv
|
|
argument will be interpreted as the initial value for the new
|
|
.Dq int
|
|
or
|
|
.Dq quad
|
|
node.
|
|
This flag does not apply to any other type of node.
|
|
The
|
|
.Fa newp
|
|
and
|
|
.Fa newlen
|
|
arguments describe the data external to SYSCTL that is to be
|
|
instrumented.
|
|
One of
|
|
.Fa func ,
|
|
.Fa qv
|
|
and the
|
|
.Dv CTLFLAG_IMMEDIATE
|
|
flag, or
|
|
.Fa newp
|
|
and
|
|
.Fa newlen
|
|
must be given for nodes that instrument data, otherwise an error is
|
|
returned.
|
|
.Pp
|
|
The remaining arguments are a list of integers specifying the path
|
|
through the MIB to the node being created.
|
|
The list must be terminated by the
|
|
.Dv CTL_EOL
|
|
value.
|
|
The penultimate value in the list may be
|
|
.Dv CTL_CREATE
|
|
if a dynamic MIB entry is to be made for this node.
|
|
.Fn sysctl_createv
|
|
specifically does not support
|
|
.Dv CTL_CREATESYM ,
|
|
since setup routines are
|
|
expected to be able to use the in-kernel
|
|
.Xr ksyms 4
|
|
interface to discover the location of the data to be instrumented.
|
|
If the node to be created matches a node that already exists, a return
|
|
code of 0 is given, indicating success.
|
|
.Pp
|
|
When using
|
|
.Fn sysctl_destroyv
|
|
to destroy a given node, the
|
|
.Fa rnode
|
|
argument, if not
|
|
.Dv NULL ,
|
|
is taken to be the root of the tree from which
|
|
the node is to be destroyed, otherwise the main tree is used.
|
|
The rest of the arguments are a list of integers specifying the path
|
|
through the MIB to the node being destroyed.
|
|
If the node being destroyed does not exist, a successful return code
|
|
is given.
|
|
Nodes marked with the
|
|
.Dv CTLFLAG_PERMANENT
|
|
flag cannot be destroyed.
|
|
.Sh HELPER FUNCTIONS AND MACROS
|
|
Helper functions are invoked with the same common argument set as
|
|
.Fn sysctl_dispatch
|
|
except that the
|
|
.Fa rnode
|
|
argument will never be
|
|
.Dv NULL .
|
|
It will be set to point to the node that corresponds most closely to
|
|
the current request.
|
|
Helpers are forbidden from modifying the node they are passed; they
|
|
should instead copy the structure if changes are required in order to
|
|
effect access control or other checks.
|
|
The
|
|
.Dq helper
|
|
prototype and function that needs to ensure that a newly assigned
|
|
value is within a certain range (presuming external data) would look
|
|
like the following:
|
|
.Pp
|
|
.Bd -literal -offset indent -compact
|
|
static int sysctl_helper(SYSCTLFN_PROTO);
|
|
.sp
|
|
static int
|
|
sysctl_helper(SYSCTLFN_ARGS)
|
|
{
|
|
struct sysctlnode node;
|
|
int t, error;
|
|
.sp
|
|
node = *rnode;
|
|
node.sysctl_data = \*[Am]t;
|
|
error = sysctl_lookup(SYSCTLFN_CALL(\*[Am]node));
|
|
if (error || newp == NULL)
|
|
return (error);
|
|
.sp
|
|
if (t \*[Lt] 0 || t \*[Gt] 20)
|
|
return (EINVAL);
|
|
.sp
|
|
*(int*)rnode-\*[Gt]sysctl_data = t;
|
|
return (0);
|
|
}
|
|
.Ed
|
|
.Pp
|
|
The use of the
|
|
.Dv SYSCTLFN_PROTO ,
|
|
.Dv SYSCTLFN_ARGS, and
|
|
.Dv SYSCTLFN_CALL
|
|
macros ensure that all arguments are passed properly.
|
|
The single argument to the
|
|
.Dv SYSCTLFN_CALL
|
|
macro is the pointer to the node being examined.
|
|
.Pp
|
|
Three basic helper functions are available for use.
|
|
.Fn sysctl_needfunc
|
|
will emit a warning to the system console whenever it is invoked and
|
|
provides a simplistic read-only interface to the given node.
|
|
.Fn sysctl_notavail
|
|
will forward
|
|
.Dq queries
|
|
to
|
|
.Fn sysctl_query
|
|
so that subtrees can be discovered, but will return
|
|
.Er EOPNOTSUPP
|
|
for any other condition.
|
|
.Fn sysctl_null
|
|
specifically ignores any arguments given, sets the value indicated by
|
|
.Fa oldlenp
|
|
to zero, and returns success.
|
|
.Sh SETUP FUNCTIONS
|
|
Though nodes can be added to the SYSCTL tree at any time, in order to
|
|
add nodes during the kernel bootstrap phase, a proper
|
|
.Dq setup
|
|
function must be used.
|
|
Setup functions are declared using the
|
|
.Dv SYSCTL_SETUP
|
|
macro, which takes the name of the function and a short string
|
|
description of the function as arguments.
|
|
.Po
|
|
See the
|
|
.Dv SYSCTL_DEBUG_SETUP
|
|
kernel configuration in
|
|
.Xr options 4 .
|
|
.Pc
|
|
The address of the function is added to a list of functions that
|
|
.Fn sysctl_init
|
|
traverses during initialization.
|
|
.Pp
|
|
Setup functions do not have to add nodes to the main tree, but can set
|
|
up their own trees for emulation or other purposes.
|
|
Emulations that require use of a main tree but with some nodes changed
|
|
to suit their own purposes can arrange to overlay a sparse private
|
|
tree onto their main tree by making the
|
|
.Fa e_sysctlovly
|
|
member of their struct emul definition point to the overlaid tree.
|
|
.Pp
|
|
Setup functions should take care to create all nodes from the root
|
|
down to the subtree they are creating, since the order in which setup
|
|
functions are called is arbitrary (the order in which setup functions
|
|
are called is only determined by the ordering of the object files as
|
|
passed to the linker when the kernel is built).
|
|
.Sh MISCELLANEOUS FUNCTIONS
|
|
.Fn sysctl_init
|
|
is called early in the kernel bootstrap process.
|
|
It initializes the SYSCTL lock, calls all the registered setup
|
|
functions, and marks the tree as permanent.
|
|
.Pp
|
|
.Fn sysctl_free
|
|
will unconditionally delete any and all nodes below the given node.
|
|
Its intended use is for the deletion of entire trees, not subtrees.
|
|
If a subtree is to be removed,
|
|
.Fn sysctl_destroy
|
|
or
|
|
.Fn sysctl_destroyv
|
|
should be used to ensure that nodes not owned by the sub-system being
|
|
deactivated are not mistakenly destroyed.
|
|
The SYSCTL lock must be held when calling this function.
|
|
.Pp
|
|
.Fn sysctl_teardown
|
|
unwinds a sysctllog and deletes the nodes in the opposite order in
|
|
which they were created.
|
|
.Pp
|
|
.Fn old_sysctl
|
|
provides an interface similar to the old SYSCTL implementation, with
|
|
the exception that access checks on a per-node basis are performed if
|
|
the
|
|
.Fa l
|
|
argument is
|
|
.No non- Ns Dv NULL .
|
|
If called with a
|
|
.Dv NULL
|
|
argument, the values for
|
|
.Fa newp
|
|
and
|
|
.Fa oldp
|
|
are interpreted as kernel addresses, and access is performed as for
|
|
the superuser.
|
|
.Sh NOTES
|
|
It is expected that nodes will be added to (or removed from) the tree
|
|
during the following stages of a machine's lifetime:
|
|
.Pp
|
|
.Bl -bullet -compact
|
|
.It
|
|
initialization -- when the kernel is booting
|
|
.It
|
|
autoconfiguration -- when devices are being probed at boot time
|
|
.It
|
|
.Dq plug and play
|
|
device attachment -- when a PC-Card, USB, or other device is plugged
|
|
in or attached
|
|
.It
|
|
LKM initialization -- when an LKM is being loaded
|
|
.It
|
|
.Dq run-time
|
|
-- when a process creates a node via the
|
|
.Xr sysctl 3
|
|
interface
|
|
.El
|
|
.Pp
|
|
Nodes marked with
|
|
.Dv CTLFLAG_PERMANENT
|
|
can only be added to a tree during the first or initialization phase,
|
|
and can never be removed.
|
|
The initialization phase terminates when the main tree's root is
|
|
marked with the
|
|
.Dv CTLFLAG_PERMANENT
|
|
flag.
|
|
Once the main tree is marked in this manner, no nodes can be added to
|
|
any tree that is marked with
|
|
.Dv CTLFLAG_READONLY
|
|
at its root, and no nodes can be added at all if the main tree's root
|
|
is so marked.
|
|
.Pp
|
|
Nodes added by device drivers, LKMs, and at device insertion time can
|
|
be added to (and removed from)
|
|
.Dq read-only
|
|
parent nodes.
|
|
.Pp
|
|
Nodes created by processes can only be added to
|
|
.Dq writable
|
|
parent nodes.
|
|
See
|
|
.Xr sysctl 3
|
|
for a description of the flags that are allowed to be used by
|
|
when creating nodes.
|
|
.Sh SEE ALSO
|
|
.Xr sysctl 3
|
|
.Sh HISTORY
|
|
The dynamic SYSCTL implementation first appeared in
|
|
.Nx 2.0 .
|
|
.Sh AUTHORS
|
|
.An Andrew Brown
|
|
.Aq atatat@NetBSD.org
|
|
designed and implemented the dynamic SYSCTL implementation.
|