Add new device method to free the automatically

allocated softc structure which is returned by
device_get_softc(). This method can be used to
easily implement softc refcounting. This can be
desirable when the softc has memory references
which are controlled by userspace handles for
example.

This solves the problem of blocking the caller
of device_detach() for a non-deterministic time.

Discussed with:	kib, ed
MFC after:	2 weeks

2 files changed, 25 insertions, 4 deletions

diff --git a/sys/kern/device_if.m b/sys/kern/device_if.m
index eb720eb..edec42b 100644
--- a/sys/kern/device_if.m
+++ b/sys/kern/device_if.m
@@ -316,3 +316,14 @@ METHOD int resume {
 METHOD int quiesce {
 	device_t dev;
 } DEFAULT null_quiesce;
+
+/**
+ * @brief Free the device softc
+ *
+ * @param _dev		device pointer
+ * @param _softc	pointer to softc
+ */
+METHOD void free_softc {
+	device_t	_dev;
+	void		*_softc;
+} DEFAULT device_free_softc;
diff --git a/sys/kern/subr_bus.c b/sys/kern/subr_bus.c
index def1652..1356684 100644
--- a/sys/kern/subr_bus.c
+++ b/sys/kern/subr_bus.c
@@ -2406,8 +2406,8 @@ device_get_softc(device_t dev)
 void
 device_set_softc(device_t dev, void *softc)
 {
-	if (dev->softc && !(dev->flags & DF_EXTERNALSOFTC))
-		free(dev->softc, M_BUS_SC);
+	if (dev->softc != NULL && !(dev->flags & DF_EXTERNALSOFTC))
+		DEVICE_FREE_SOFTC(dev, dev->softc);
 	dev->softc = softc;
 	if (dev->softc)
 		dev->flags |= DF_EXTERNALSOFTC;
@@ -2604,8 +2604,8 @@ device_set_driver(device_t dev, driver_t *driver)
 	if (dev->driver == driver)
 		return (0);
 
-	if (dev->softc && !(dev->flags & DF_EXTERNALSOFTC)) {
-		free(dev->softc, M_BUS_SC);
+	if (dev->softc != NULL && !(dev->flags & DF_EXTERNALSOFTC)) {
+		DEVICE_FREE_SOFTC(dev, dev->softc);
 		dev->softc = NULL;
 	}
 	device_set_desc(dev, NULL);
@@ -4797,3 +4797,13 @@ bus_free_resource(device_t dev, int type, struct resource *r)
 		return (0);
 	return (bus_release_resource(dev, type, rman_get_rid(r), r));
 }
+
+/*
+ * The "dev" argument passed to "device_free_softc()" is allowed to be
+ * NULL, if the device freeing the soft is not available.
+ */
+void
+device_free_softc(device_t dev, void *softc)
+{
+	free(softc, M_BUS_SC);
+}