Updated: 2021/Apr/14


AUTOCONF(9)                Kernel Developer's Manual               AUTOCONF(9)

NAME
     autoconf, config_search, config_found, config_match, config_attach,
     config_attach_pseudo, config_detach, config_detach_children,
     config_deactivate, config_defer, config_interrupts, config_mountroot,
     config_pending_incr, config_pending_decr, config_finalize_register -
     autoconfiguration framework

SYNOPSIS
     #include <sys/param.h>
     #include <sys/device.h>
     #include <sys/errno.h>

     cfdata_t
     config_search(device_t parent, void *aux, const struct cfargs *);

     device_t
     config_found(device_t parent, void *aux, cfprint_t print,
         const struct cfargs *);

     int
     config_match(device_t parent, cfdata_t cf, void *aux);

     int
     config_probe(device_t parent, cfdata_t cf, void *aux);

     device_t
     config_attach(device_t parent, cfdata_t cf, void *aux, cfprint_t print,
         const struct cfargs *);

     device_t
     config_attach_pseudo(cfdata_t cf);

     int
     config_detach(device_t dev, int flags);

     int
     config_detach_children(device_t dev, int flags);

     int
     config_deactivate(device_t dev);

     int
     config_defer(device_t dev, void (*func)(device_t));

     void
     config_interrupts(device_t dev, void (*func)(device_t));

     void
     config_mountroot(device_t dev, void (*func)(device_t));

     void
     config_pending_incr();

     void
     config_pending_decr();

     int
     config_finalize_register(device_t dev, int (*func)(device_t));

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 busses.

     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(1).  For a
     description of the config(1) "device definition" language, see config(9).

     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.

     Several of the autoconfiguration functions take a strongly-typed variadic
     list of arguments to pass information from driver autoconfiguration
     functions to the kernel's autoconfiguration system.  This list is
     constructed using the CFARGS() macro, like this example:

           config_search(self, NULL,
               CFARGS(.search = mainbus_search,
                      .iattr = "mainbus"));

     Each tag is followed by a tag-specific value.

           submatch       A pointer to a `submatch' function used in direct
                          configuration.

           search         A pointer to a `search' function used in indirect
                          configuration.

           iattr          A pointer to a constant C string (const char *)
                          specifying an interface attribute.  If a parent
                          device carries only a single interface attribute,
                          then this argument may be omitted.  If an interface
                          attribute is specified that the parent device does
                          not carry, or no interface attribute is specified
                          and the parent device carries more than one,
                          behavior is undefined.  On kernels built with the
                          DIAGNOSTIC option, this may result in an assertion
                          panic.

           locators       A pointer to a constant array of integers (const int
                          *) containing interface attribute-specific locators.

           devhandle      A devhandle_t (passed by value) corresponding to the
                          device being attached.

     If no arguments are to be passed, the special value CFARGS_NONE may be
     used in place of the CFARGS() macro.

FUNCTIONS
     config_search(parent, aux, cfargs)
                 Cfargs consumed: search, iattr, locators.

                 Performs indirect configuration of physical devices.
                 config_search() iterates over all potential children, calling
                 the given search function If no search function is specified,
                 applies the potential child's match function instead.  The
                 argument parent is the pointer to the parent's device
                 structure.  If an interface attribute is specified, only
                 potential children eligible to attach to that interface
                 attribute will be consulted.  If specified, the locators
                 argument lists the locator values for the device and are
                 passed to the search function.  The given aux argument
                 describes the device that has been found and is simply passed
                 on through the search function to the child.  config_search()
                 returns a pointer to the configuration data that indicates
                 the best-matched child or NULL otherwise.

                 The role of the search function is to call config_probe() for
                 each potential child and call config_attach() for any
                 positive matches.  If no search function is specified, 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.

     config_found(parent, aux, print, cfargs)
                 Cfargs consumed: submatch, iattr, locators, devhandle.

                 Performs direct configuration on a physical device.
                 config_found() is called by the parent and in turn calls the
                 specified submatch function as determined by the
                 configuration table.  The submatch function compares user-
                 specified locators from the machine description file against
                 those specifying a found device, calling config_match() if
                 they match (including wildcard matching).  If a submatch
                 function is not specified, then driver match functions are
                 called directly.  The argument parent is the pointer to the
                 parent's device structure.  If an interface attribute is
                 specified, only potential children eligible to attach to that
                 interface attribute will be consulted.  If specified, the
                 locators argument lists the locator values for the found
                 device and may be used by the submatch function and will be
                 recorded in the device structure of the child device.  The
                 given aux argument describes the device that has been found.
                 config_found() internally uses config_search().  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.  The print function must
                 return an integer value.

                 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.  If a device handle
                 is specified, that handle will be associated with the
                 resulting child device structure if a driver matches.

                 config_found() returns a pointer to the attached device's
                 device structure if the device is attached, NULL otherwise.
                 Most callers can ignore this value, since the system will
                 already have printed a diagnostic.

     config_match(parent, cf, aux)
                 Match a device (direct configuration).  Invokes the driver's
                 match function according to the configuration table.  The
                 config_match() function returns a nonzero integer indicating
                 the confidence of supporting this device and a value of 0 if
                 the driver doesn't support the device.

     config_probe(parent, cf, aux)
                 Probe for a device (indirect configuration).  Invokes the
                 driver's match function according to the configuration table.
                 The config_probe() function returns a nonzero integer to
                 indicate a successful probe and a value of 0 otherwise.
                 Unlike config_match(), the return value of config_probe() is
                 not intended to reflect a confidence value.

     config_attach(parent, cf, aux, print, cfargs)
                 Cfargs consumed: locators, devhandle.

                 Attach a found device.  Allocates the memory for the softc
                 structure and calls the drivers attach function according to
                 the configuration table.  If successful, config_attach()
                 returns a pointer to the device structure.  If unsuccessful,
                 it returns NULL.

     config_attach_pseudo(cf)
                 Create an instance of a pseudo-device driver.  config(5)
                 syntax allows the creation of pseudo-devices from which
                 regular device_t instances can be created.  Such objects are
                 similar to the devices that attach at the root of the device
                 tree.

                 The caller is expected to allocate and fill the cfdata_t
                 object and pass it to config_attach_pseudo().  The content of
                 that object is similar to what is returned by config_search()
                 for regular devices.

     config_detach(dev, flags)
                 Called by the parent to detach the child device.  The second
                 argument flags contains detachment flags.  Valid values are
                 DETACH_FORCE (force detachment, e.g., because of hardware
                 removal) and DETACH_QUIET (do not print a notice).
                 config_detach() returns zero if successful and an error code
                 otherwise.  config_detach() is always called from a thread
                 context, allowing condition variables to be used while the
                 device detaches itself.

     config_detach_children(dev, flags)
                 Iterate through all attached devices, calling config_detach()
                 for each child of dev, passing flags.  If detaching any child
                 results in an error, the iteration will halt and any
                 remaining devices will not be detached.
                 config_detach_children() returns zero if successful and an
                 error code otherwise.

     config_deactivate(dev)
                 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(dev, func)
                 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.

     config_interrupts(dev, func)
                 Called by the child to defer the remainder of its
                 configuration until interrupts are enabled.  At this point,
                 the function func is called with the argument dev.

     config_mountroot(dev, func)
                 Called by the child to defer the remainder of its
                 configuration until the root file system is mounted.  At this
                 point, the function func is called with the argument dev.
                 This is used for devices that need to load firmware image
                 from a mounted file system.

     config_pending_incr()
                 Increment the config_pending semaphore.  It is used to
                 account for deferred configurations before mounting the root
                 file system.

     config_pending_decr()
                 Decrement the config_pending semaphore.  It is used to
                 account for deferred configurations before mounting the root
                 file system.

     config_finalize_register(dev, func)
                 Register a function to be called after all real devices have
                 been found.

                 Registered functions are all executed until all of them
                 return 0.  The callbacks should return 0 to indicate they do
                 not require to be called another time, but they should be
                 aware that they still might be in case one of them returns 1.

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
     config(1), config(5), condvar(9), config(9), driver(9)

HISTORY
     Autoconfiguration first appeared in 4.1BSD.  The autoconfiguration
     framework was completely revised in 4.4BSD.  The detach and deactivate
     interfaces appeared in NetBSD 1.5.

NetBSD 9.99                     August 7, 2021                     NetBSD 9.99