MFC 305034: Implement 'devctl clear driver' to undo a previous 'set driver'.

Add a new 'clear driver' command for devctl along with the accompanying
ioctl and devctl_clear_driver() library routine to reset a device to
use a wildcard devclass instead of a fixed devclass.  This can be used
to undo a previous 'set driver' command.  After the device's name has
been reset to permit wildcard names, it is reprobed so that it can
attach to newly-available (to it) device drivers.

Sponsored by:	Chelsio Communications

3 files changed, 51 insertions, 3 deletions

diff --git a/lib/libdevctl/devctl.3 b/lib/libdevctl/devctl.3
index 866bb6a..a4fe062 100644
--- a/lib/libdevctl/devctl.3
+++ b/lib/libdevctl/devctl.3
@@ -25,12 +25,13 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd April 27, 2016
+.Dd August 29, 2016
 .Dt DEVCTL 3
 .Os
 .Sh NAME
 .Nm devctl ,
 .Nm devctl_attach ,
+.Nm devctl_clear_driver ,
 .Nm devctl_delete ,
 .Nm devctl_detach ,
 .Nm devctl_disable ,
@@ -47,6 +48,8 @@
 .Ft int
 .Fn devctl_attach "const char *device"
 .Ft int
+.Fn devctl_clear_driver "const char *device" "bool force"
+.Ft int
 .Fn devctl_delete "const char *device" "bool force"
 .Ft int
 .Fn devctl_detach "const char *device" "bool force"
@@ -166,12 +169,30 @@ the device will be detached from its current device driver before it is
 attached to the new device driver.
 .Pp
 The
+.Fn devctl_clear_driver
+function resets a device so that it can be attached to any valid device
+driver rather than only drivers with a previously specified name.
+This function is used to undo a previous call to
+.Fn devctl_set_driver .
+If the device is already attached and
+.Fa force
+is false,
+the request will fail.
+If the device is already attached and
+.Fa force
+is true,
+the device will be detached from its current device driver.
+After the device's name is reset,
+it is reprobed and attached to a suitable device driver if one is found.
+.Pp
+The
 .Fn devctl_rescan
 function rescans a bus device checking for devices that have been added or
 removed.
 .Sh RETURN VALUES
-.Rv -std devctl_attach devctl_delete devctl_detach devctl_disable \
-devctl_enable devctl_suspend devctl_rescan devctl_resume devctl_set_driver
+.Rv -std devctl_attach devctl_clear_driver devctl_delete devctl_detach \
+devctl_disable devctl_enable devctl_suspend devctl_rescan devctl_resume \
+devctl_set_driver
 .Sh ERRORS
 In addition to specific errors noted below,
 all of the
@@ -302,6 +323,24 @@ The new device driver failed to attach.
 .El
 .Pp
 The
+.Fn devctl_clear_driver
+function may fail if:
+.Bl -tag -width Er
+.It Bq Er EBUSY
+The device is currently attached to a device driver and
+.Fa force
+is false.
+.It Bq Er EBUSY
+The current device driver for
+.Fa device
+is busy and cannot detach at this time.
+.It Bq Er EINVAL
+The device is not configured for a specific device driver name.
+.It Bq Er ENXIO
+The device driver chosen after reprobing failed to attach.
+.El
+.Pp
+The
 .Fn devctl_rescan
 function may fail if:
 .Bl -tag -width Er
diff --git a/lib/libdevctl/devctl.c b/lib/libdevctl/devctl.c
index 9f275e7..5013fb0 100644
--- a/lib/libdevctl/devctl.c
+++ b/lib/libdevctl/devctl.c
@@ -124,6 +124,14 @@ devctl_set_driver(const char *device, const char *driver, bool force)
 }
 
 int
+devctl_clear_driver(const char *device, bool force)
+{
+
+	return (devctl_simple_request(DEV_CLEAR_DRIVER, device, force ?
+	    DEVF_CLEAR_DRIVER_DETACH : 0));
+}
+
+int
 devctl_rescan(const char *device)
 {
 
diff --git a/lib/libdevctl/devctl.h b/lib/libdevctl/devctl.h
index 670ca1a..d49199a 100644
--- a/lib/libdevctl/devctl.h
+++ b/lib/libdevctl/devctl.h
@@ -38,6 +38,7 @@ int	devctl_disable(const char *device, bool force_detach);
 int	devctl_suspend(const char *device);
 int	devctl_resume(const char *device);
 int	devctl_set_driver(const char *device, const char *driver, bool force);
+int	devctl_clear_driver(const char *device, bool force);
 int	devctl_rescan(const char *device);
 int	devctl_delete(const char *device, bool force);