AUTOCONF(9) OpenBSD Kernel Manual AUTOCONF(9)NAMEautoconf - autoconfiguration framework
Autoconfiguration is the process of matching hardware devices with an
appropriate device driver. In its most basic form, autoconfiguration
consists of the recursive process of finding and attaching all devices on
a bus, including other buses.
The autoconfiguration framework supports direct configuration where the
bus driver can determine the devices present.
The autoconfiguration framework also supports indirect configuration
where the drivers must probe the bus looking for the presence of a
device. Direct configuration is preferred since it can find hardware
regardless of the presence of proper drivers.
The autoconfiguration process occurs at system bootstrap and is driven by
a table generated from a ``machine description'' file by config(8). For
a description of the config(8) ``device definition'' language, see
Each device must have a name consisting of an alphanumeric string that
ends with a unit number. The unit number identifies an instance of the
driver. Device data structures are allocated dynamically during
autoconfiguration, giving a unique address for each instance.
The config_init() function initializes the autoconfiguration data
config_search(cfmatch_t func, struct device *parent, void *aux);
config_rootsearch(cfmatch_t func, char *rootname, void *aux);
The config_search() function performs indirect configuration of physical
devices by iterating over all potential children, calling the given
function func for each one.
The config_rootsearch() function finds the root device identified by the
string rootname, in a manner similar to config_search(), except that
there is no parent device. If func is NULL, config_search() applies each
child's match function instead. The argument parent is the pointer to
the parent's device structure. The given aux argument describes the
device that has been found and is simply passed on through func to the
child. config_search() returns a pointer to the best-matched child or
The role of func is to call the match function for each device and call
config_attach() for any positive matches.
typedef int (*cfmatch_t)(struct device *parent, void *child, void *aux);
If func is NULL, then the parent should record the return value from
config_search() and call config_attach() itself.
Note that this function is designed so that it can be used to apply an
arbitrary function to all potential children. In this case callers may
choose to ignore the return value.
struct device *
config_found_sm(struct device *parent, void *aux, cfprint_t
print, cfmatch_t submatch);
struct device *
config_found(struct device *parent, void *aux, cfprint_t print);
struct device *
config_rootfound(char *rootname, void *aux);
The config_found_sm() function performs direct configuration on a
physical device. config_found_sm() is called by the parent and in turn
calls the submatch function to call the match function as determined by
the configuration table. If submatch is NULL, the driver match functions
are called directly. The argument parent is the pointer to the parent's
device structure. The given aux argument describes the device that has
been found. The softc structure for the matched device will be
allocated, and the appropriate driver attach function will be called.
If the device is matched, the system prints the name of the child and
parent devices, and then calls the print function to produce additional
information if desired. If no driver takes a match, the same print
function is called to complain. The print function is called with the
aux argument and, if the matches failed, the full name (including unit
number) of the parent device, otherwise NULL.
typedef int (*cfprint_t)(void *aux, const char *parentname);
#define QUIET 0 /* print nothing */
#define UNCONF 1 /* print " not configured" */
#define UNSUPP 2 /* print " not supported" */
Two special strings, ``not configured'' and ``unsupported'' will be
appended automatically to non-driver reports if the return value is
UNCONF or UNSUPP respectively, otherwise the function should return the
The config_found_sm() function returns a pointer to the attached device's
softc structure if the device is attached, NULL otherwise. Most callers
can ignore this value, since the system will already have printed a
The config_found() macro expands to config_found_sm(parent, aux, print,
submatch) with submatch set to NULL and is provided for compatibility
with older drivers.
The config_rootfound() function performs the same operation on the root
device identified by the rootname string.
ATTACHING AND DETACHING DEVICES
struct device *
config_attach(struct device *parent, void *cf, void *aux, cfprint_t
config_detach(struct device *dev, int flags);
The config_attach() function attaches a found device. Memory is
allocated for the softc structure and the driver's attach function is
called according to the configuration table. If successful,
config_attach() returns the softc. If unsuccessful, it returns NULL.
The config_detach() function is called by the parent to detach the child
device. The second argument flags contains detachment flags:
#define DETACH_FORCE 0x01 /* Force detachment; hardware gone */
#define DETACH_QUIET 0x02 /* Don't print a notice */
The config_detach() function returns zero if successful and an error code
otherwise. config_detach() is always called from process context,
allowing tsleep(9) to be called while the device detaches itself (to deal
with processes which have a device open).
config_activate(struct device *dev);
config_deactivate(struct device *dev);
The config_activate() function is called by the parent to activate the
child device dev. It is called to activate resources and initialise
other kernel subsystems (such as the network subsystem).
config_activate() is called from interrupt context after the device has
The config_deactivate() function is called by the parent to deactivate
the child device dev. config_deactivate() is called from interrupt
context to immediately relinquish resources and notify dependent kernel
subsystems that the device is about to be detached. At some later point,
config_detach() will be called to finalise the removal of the device.
config_defer(struct device *dev, void (*func)(struct device *));
The config_defer() function is called by the child to defer the remainder
of its configuration until all its parent's devices have been attached.
At this point, the function func is called with the argument dev.
The autoconfiguration framework itself is implemented within the file
sys/kern/subr_autoconf.c. Data structures and function prototypes for
the framework are located in sys/sys/device.h.
SEE ALSOautoconf(4), files.conf(5), config(8)HISTORY
Autoconfiguration first appeared in 4.1BSD. The autoconfiguration
framework was completely revised in 4.4BSD. The detach and
activate/deactivate interfaces appeared in NetBSD 1.5.
OpenBSD 4.9 June 26, 2008 OpenBSD 4.9