CONFIG_SEARCH(9) | Kernel Developer's Manual | CONFIG_SEARCH(9)

# NAME

`config_search`, `config_rootsearch`, `config_found_sm`, `config_found`, `config_rootfound` — autoconfiguration framework

# SYNOPSIS

`#include <sys/param.h>`
`#include <sys/device.h>`

void *
`config_search`(cfmatch_t func, struct device *parent, void *aux);

void *
`config_rootsearch`(cfmatch_t func, char *rootname, void *aux);

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);

# DESCRIPTION

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 files.conf(5).

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.

## Indirect Configuration

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 `NULL` otherwise.

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.

## Direct Configuration

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 value `QUIET`.

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 diagnostic.

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.

# CODE REFERENCES

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 ALSO

autoconf(4), files.conf(5), config(8), config_attach(9)

# HISTORY

Autoconfiguration first appeared in 4.1BSD. The autoconfiguration framework was completely revised in 4.4BSD.

June 13, 2025 | Debian