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Add caveats about adding devices in the IDENTIFY context.

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This commit is contained in:
Warner Losh 2004-05-13 20:29:40 +00:00
parent aebc6093f9
commit cf39dca90c
1 changed files with 17 additions and 3 deletions
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20
share/man/man9/device_add_child.9
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@ -28,7 +28,7 @@
.\"
.\" $FreeBSD$
.\"
.Dd June 16, 1998
.Dd May 13, 2004
.Dt DEVICE_ADD_CHILD 9
.Os
.Sh NAME
@ -59,8 +59,9 @@ 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.
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.
.Pp
This allows busses which can uniquely identify device instances (such
as PCI) to allow each driver to check each device instance for a
@ -92,6 +93,19 @@ order.
If
.Fn device_add_child
is used, then the new child will be added as if its order was zero.
.Pp
When adding a device in the context of
.Xr DEVICE_IDENTIFY 9
routine, some care must be taken to ensure that the device hasn't
already been added to the tree.
Because the device name and
.Ft 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.
.Sh RETURN VALUES
The new device if successful, NULL otherwise.
.Sh SEE ALSO