AUTOCONF(9) BSD Kernel Developer's Manual AUTOCONF(9)
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 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 autocon-
figuration, giving a unique address for each instance.
void * config_search(cfmatch_t func, struct device *parent, void *aux)
void * 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 func-
tion 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 physi-
cal 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 allo-
cated, 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 func-
tion is called to complain. The print function is called with the aux
argument and, if the matches failed, the full name (including unit num-
ber) 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 diag-
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.
void 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.
autoconf(4), files.conf(5), config(8), config_attach(9)
Autoconfiguration first appeared in 4.1BSD. The autoconfiguration frame-
work was completely revised in 4.4BSD.
BSD July 13, 2014 BSD