SYSCTL(9) | Kernel Developer's Manual | SYSCTL(9) |
sysctl
—
#include <sys/param.h>
#include <sys/sysctl.h>
Primary external interfaces:
void
sysctl_init
(void);
int
sysctl_lock
(struct
lwp *l, void *oldp,
size_t savelen);
int
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);
void
sysctl_unlock
(struct
lwp *l);
int
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,
...);
int
sysctl_destroyv
(struct
sysctlnode *rnode,
...);
void
sysctl_free
(struct
sysctlnode *rnode);
void
sysctl_teardown
(struct
sysctllog **);
int
old_sysctl
(int
*name, u_int
namelen, void
*oldp, size_t
*oldlenp, void
*newp, size_t
newlen, struct lwp
*l);
Core internal functions:
int
sysctl_locate
(struct
lwp *l, const int
*name, u_int
namelen, const struct
sysctlnode **rnode, int
*nip);
int
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);
int
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);
int
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);
int
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);
Simple “helper” functions:
int
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);
int
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);
int
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);
sysctl_lock
(),
sysctl_createv
(),
sysctl_destroyv
(), and
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
sysctl_lock
() with a pointer to the process's lwp
l (NULL
may be passed to all
functions as the lwp pointer if no lwp is appropriate, though any changes made
via sysctl_create
(),
sysctl_destroy
(),
sysctl_lookup
(), or by any helper function will be
done with effective superuser privileges).
The oldp and 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
NULL
and 0, respectively.
The memory region will be locked via
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 sysctl_unlock
(), only the lwp
pointer l is required.
sysctl_dispatch
() to handle the request.
sysctl_dispatch
() will examine the contents of
name, an array of integers at least
namelen long, which is to be located in kernel space, in
order to determine which function to call to handle the specific request.
The following algorithm is used by
sysctl_dispatch
() to determine the function to
call:
sysctl_locate
().sysctl_lookup
().sysctl_query
(),
sysctl_create
(), or
sysctl_destroy
(), call the appropriate
function.EOPNOTSUPP
.The oldp and oldlenp
arguments to sysctl_dispatch
(), as with all the
other core functions, describe an area into which the current or requested
value may be copied. oldp may or may not be a pointer
into userspace (as dictated by whether l is
NULL
or not). oldlenp is a
non-NULL
pointer to a
size_t. newp and newlen describe
an area where the new value for the request may be found;
newp may also be a pointer into userspace. The
oname argument is a
non-NULL
pointer to the base
of the request currently being processed. By simple arithmetic on
name, namelen, and
oname, one can easily determine the entire original
request and namelen values, if needed. The
rnode value, as passed to
sysctl_dispatch
() represents the root of the tree
into which the current request is to be dispatched. If
NULL
, the main tree will be used.
The sysctl_locate
() function scans a tree
for the node most specific to a request. If the pointer referenced by
rnode is not NULL
, the tree
indicated is searched, otherwise the main tree will be used. The address of
the most relevant node will be returned via rnode and
the number of MIB entries consumed will be returned via
nip, if it is not NULL
.
The sysctl_lookup
() function takes the
same arguments as sysctl_dispatch
() with the caveat
that the value for namelen must be zero in order to
indicate that the node referenced by the rnode
argument is the one to which the lookup is being applied.
sysctl_create
() and
sysctl_destroy
() functions. These functions take the
same arguments as sysctl_dispatch
() with the
additional requirement that the namelen argument must be
1 and the name argument must point to an integer valued
either CTL_CREATE
or
CTL_CREATESYM
when creating a new node, or
CTL_DESTROY
when destroying a node.
The newp and 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 oldp and oldlenp. If the create operation fails because of a conflict with an existing node, a copy of that node will be returned instead.
In order to facilitate the creation and destruction of nodes from
a given tree by kernel subsystems, the functions
sysctl_createv
() and
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.
The arguments to sysctl_createv
() are used
to construct the new node. If the log argument is not
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
sysctl_teardown
()) without the need for any record
keeping on the caller's part.
The cflags argument is currently unused and
must be zero. The rnode argument must either be
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
NULL
, the main tree will be used. It is illegal for
rnode to refer to a NULL
pointer. If the cnode argument is not
NULL
, on return it will be adjusted to point to the
address of the new node.
The flags and type
arguments are combined into the sysctl_flags field,
and the current value for SYSCTL_VERSION
is added
in. The following types are defined:
CTLTYPE_NODE
CTLTYPE_INT
CTLTYPE_STRING
CTLTYPE_QUAD
CTLTYPE_STRUCT
CTLTYPE_BOOL
The namep argument is copied into the
sysctl_name field and must be less than
SYSCTL_NAMELEN
characters in length. The string
indicated by desc will be copied if the
CTLFLAG_OWNDESC
flag is set, and will be used as the
node's description.
Two additional remarks:
CTLFLAG_PERMANENT
flag can only be set from
SYSCTL setup routines (see SETUP
FUNCTIONS) as called by sysctl_init
().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
sysctl_destroyv
() will set the
CTLFLAG_OWNDESC
flag.The func argument is the name of a
“helper” function (see
HELPER FUNCTIONS AND
MACROS). If the CTLFLAG_IMMEDIATE
flag is set,
the qv argument will be interpreted as the initial
value for the new “bool”, “int” or
“quad” node. This flag does not apply to any other type of
node. The newp and newlen
arguments describe the data external to SYSCTL that is to be instrumented.
One of func, qv and the
CTLFLAG_IMMEDIATE
flag, or
newp and newlen must be given
for nodes that instrument data, otherwise an error is returned.
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 CTL_EOL
value. The penultimate value in the list
may be CTL_CREATE
if a dynamic MIB entry is to be
made for this node. sysctl_createv
() specifically
does not support CTL_CREATESYM
, since setup routines
are expected to be able to use the in-kernel
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.
When using sysctl_destroyv
() to destroy a
given node, the rnode argument, if not
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
CTLFLAG_PERMANENT
flag cannot be destroyed.
sysctl_dispatch
() except that the
rnode argument will never be
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
“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:
static int sysctl_helper(SYSCTLFN_PROTO); static int sysctl_helper(SYSCTLFN_ARGS) { struct sysctlnode node; int t, error; t = *(int *)rnode->sysctl_data; node = *rnode; node.sysctl_data = &t; error = sysctl_lookup(SYSCTLFN_CALL(&node)); if (error || newp == NULL) return (error); if (t < 0 || t > 20) return (EINVAL); *(int *)rnode->sysctl_data = t; return (0); }
The use of the SYSCTLFN_PROTO
,
SYSCTLFN_ARGS, and
SYSCTLFN_CALL
macros ensure that all arguments are passed properly. The single argument to
the SYSCTLFN_CALL
macro is the pointer to the node
being examined.
Three basic helper functions are available for use.
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. sysctl_notavail
() will forward
“queries” to sysctl_query
() so that
subtrees can be discovered, but will return
EOPNOTSUPP
for any other condition.
sysctl_null
() specifically ignores any arguments
given, sets the value indicated by oldlenp to zero,
and returns success.
SYSCTL_SETUP
macro, which takes the name of the
function and a short string description of the function as arguments. (See the
SYSCTL_DEBUG_SETUP
kernel configuration in
options(4).) The address of the
function is added to a list of functions that
sysctl_init
() traverses during initialization.
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 e_sysctlovly member of their struct emul definition point to the overlaid tree.
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).
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.
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,
sysctl_destroy
() or
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.
sysctl_teardown
() unwinds a
sysctllog and deletes the nodes in the opposite order in
which they were created.
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 l argument is
non-NULL
. If called with a
NULL
argument, the values for
newp and oldp are interpreted as
kernel addresses, and access is performed as for the superuser.
Nodes marked with 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 CTLFLAG_PERMANENT
flag. Once
the main tree is marked in this manner, no nodes can be added to any tree
that is marked with CTLFLAG_READONLY
at its root,
and no nodes can be added at all if the main tree's root is so marked.
Nodes added by device drivers, modules, and at device insertion time can be added to (and removed from) “read-only” parent nodes.
Nodes created by processes can only be added to “writable” parent nodes. See sysctl(3) for a description of the flags that are allowed to be used by when creating nodes.
December 4, 2011 | NetBSD 9.2 |