| DEVICE_ADD_CHILD(9) | Kernel Developer's Manual | DEVICE_ADD_CHILD(9) |
device_add_child,
device_add_child_ordered —
add a new device as a child of an existing
device
#include
<sys/param.h>
#include <sys/bus.h>
device_t
device_add_child(device_t
dev, const char
*name, int
unit);
device_t
device_add_child_ordered(device_t
dev, int order,
const char *name,
int unit);
Create a new child device of dev. The
name and unit arguments specify
the name and unit number of the device. If the name is unknown then the
caller should pass NULL. If the unit is unknown then
the caller should pass -1 and the system will choose
the next available unit number.
The name of the device is used to determine which drivers might be appropriate for the device. If a name is specified then only drivers of that name are probed. If no name is given then all drivers for the owning bus are probed. In any event, only the name of the device is stored so that one may safely unload/load a driver bound to that name.
This allows buses which can uniquely identify device instances (such as PCI) to allow each driver to check each device instance for a match. For buses which rely on supplied probe hints where only one driver can have a chance of probing the device, the driver name should be specified as the device name.
Normally unit numbers will be chosen automatically by the system
and a unit number of -1 should be given. When a
specific unit number is desired (e.g., for wiring a particular piece of
hardware to a pre-configured unit number), that unit should be passed. If
the specified unit number is already allocated, a new unit will be allocated
and a diagnostic message printed.
If the devices attached to a bus
must be probed in a specific order (e.g., for the ISA bus some devices are
sensitive to failed probe attempts of unrelated drivers and therefore must
be probed first), the order argument of
device_add_child_ordered()
should be used to specify a partial ordering. The new device will be added
before any existing device with a greater order. If
device_add_child() is used, then the new child will
be added as if its order was zero.
When adding a device in the context of DEVICE_IDENTIFY(9) routine, the device_find_child(9) routine should be used to ensure that the device has not already been added to the tree. Because the device name and devclass_t are associated at probe time (not child addition time), previous instances of the driver (say in a module that was later unloaded) may have already added the instance. Authors of bus drivers must likewise be careful when adding children when they are loaded and unloaded to avoid duplication of children devices.
When adding a child to another device node,
such as in an identify routine, use BUS_ADD_CHILD(9)
instead of device_add_child(9).
BUS_ADD_CHILD(9) will call
device_add_child(9) and add the proper bus-specific data
to the new child.
device_add_child()
does not call BUS_ADD_CHILD(9).
The new device if successful, NULL otherwise.
BUS_ADD_CHILD(9), device(9), device_delete_child(9), device_find_child(9), DEVICE_IDENTIFY(9)
This manual page was written by Doug Rabson.
| February 11, 2018 | Debian |