autoconf - 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 busses.
The autoconfiguration framework supports direct
configuration where the
bus driver can determine the devices present.
The autoconfiguration framework also supports indirect
where the drivers must probe the bus looking for the presence of a device.
Direct configuration is preferred since it can find
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
a description of the config(8) ``device definition'' language, see
Each device must have a name consisting of an alphanumeric
ends with a unit number. The unit number identifies an instance of the
driver. Device data structures are allocated dynamically
giving a unique address for each instance.
The config_init() function initializes the autoconfiguration
INDIRECT CONFIGURATION [Toc] [Back]
config_search(cfmatch_t func, struct device *parent, void
config_rootsearch(cfmatch_t func, char *rootname, void
The config_search() function performs indirect configuration
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()
child's match function instead. The argument parent is the
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 bestmatched 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,
If func is NULL, then the parent should record the return
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
choose to ignore the return value.
struct device *
config_found_sm(struct device *parent, void *aux, cfprint_t
struct device *
config_found(struct device *parent, void *aux, cfprint_t
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
called directly. The argument parent is the pointer to the
structure. The given aux argument describes the device
been found. The softc structure for the matched device will
and the appropriate driver attach function will be
If the device is matched, the system prints the name of the
parent devices, and then calls the print function to produce
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 config_found_sm() function returns a pointer to the attached device's
softc structure if the device is attached, NULL otherwise.
can ignore this value, since the system will already have
printed a diagnostic.
The config_found() macro expands to config_found_sm(parent,
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 [Toc] [Back]
struct device *
config_attach(struct device *parent, void *cf, void *aux,
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,
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
#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
sleep(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
child device dev. It is called to activate resources and
kernel subsystems (such as the network subsystem).
is called from interrupt context after the device has been
The config_deactivate() function is called by the parent to
the child device dev. config_deactivate() is called from
to immediately relinquish resources and notify dependent kernel subsystems
that the device is about to be detached. At some
config_detach() will be called to finalise the removal of
DEFERRED CONFIGURATION [Toc] [Back]
config_defer(struct device *dev, void (*func)(struct device
The config_defer() function is called by the child to defer
of its configuration until all its parent's devices have
At this point, the function func is called with the argument
The autoconfiguration framework itself is implemented within
sys/kern/subr_autoconf.c. Data structures and function prototypes for
the framework are located in sys/sys/device.h.
autoconf(4), files.conf(5), config(8)
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 3.6 August 25, 2002
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