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SubjectRe: Implement class_device_update_dev() function
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Hi Kay,

> > > > > But userspace should also find out about this change, and this patch
> > > > > prevents that from happening. What about just tearing down the class
> > > > > device and creating a new one? That way userspace knows about the new
> > > > > linkage properly, and any device naming and permission issues can be
> > > > > handled anew?
> > > >
> > > > This won't work for Bluetooth. We create the TTY and its class device
> > > > with tty_register_device() and then the device node is present. Then at
> > > > some point later we open that device and the Bluetooth connection gets
> > > > established. Only when the connection has been established we know the
> > > > device that represents it. So tearing down the class device and creating
> > > > a new one will screw up the application that is using this device node.
> > > >
> > > > Would reissuing the uevent of the class device help here?
> > >
> > > How about KOBJ_ONLINE/OFFLINE?
> >
> > I am not that familiar with the internals of kobject. Can you give me an
> > example on how to do that?
>
> Just send another event (but not add or remove), for the already created
> object. CPU hotplug uses ONLINE/OFFLINE, and we also use it to get
> notified when the device mapper table is set up (not upstream). Udev is
> able to update symlinks, or run actions on "online" events if asked
> for.

the attached patch sends ONLINE when a device has been attached to a
class device and OFFLINE when it has been removed.

Regards

Marcel

[PATCH] Allow dynamically changing the device of a class device

This patch implements the class_device_update_dev() function which
allows to change the device of a class device after its creation.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

---
commit 97372f657bbb68ee1c4119bb21642fc700317ce3
tree bd46b493dd75b09515897eb0d12b2fd30a234e3c
parent 120bda20c6f64b32e8bfbdd7b34feafaa5f5332e
author Marcel Holtmann <marcel@holtmann.org> Sat, 08 Jul 2006 15:24:15 +0200
committer Marcel Holtmann <marcel@holtmann.org> Sat, 08 Jul 2006 15:24:15 +0200

drivers/base/class.c | 98 ++++++++++++++++++++++++++++++++++--------------
include/linux/device.h | 1
2 files changed, 71 insertions(+), 28 deletions(-)

diff --git a/drivers/base/class.c b/drivers/base/class.c
index de89083..1789a6b 100644
--- a/drivers/base/class.c
+++ b/drivers/base/class.c
@@ -485,6 +485,48 @@ static void class_device_remove_groups(s
}
}

+static int class_device_add_dev(struct class_device *class_dev)
+{
+ char *class_name = NULL;
+ int error = 0;
+
+ if (class_dev->dev) {
+ class_name = make_class_name(class_dev->class->name,
+ &class_dev->kobj);
+ error = sysfs_create_link(&class_dev->kobj,
+ &class_dev->dev->kobj, "device");
+ if (error)
+ goto out;
+
+ error = sysfs_create_link(&class_dev->dev->kobj,
+ &class_dev->kobj, class_name);
+ if (error) {
+ sysfs_remove_link(&class_dev->kobj, "device");
+ goto out;
+ }
+
+ kobject_uevent(&class_dev->kobj, KOBJ_ONLINE);
+ }
+
+ out:
+ kfree(class_name);
+ return error;
+}
+
+static void class_device_remove_dev(struct class_device *class_dev)
+{
+ char *class_name;
+
+ if (class_dev->dev) {
+ class_name = make_class_name(class_dev->class->name,
+ &class_dev->kobj);
+ sysfs_remove_link(&class_dev->kobj, "device");
+ sysfs_remove_link(&class_dev->dev->kobj, class_name);
+ kobject_uevent(&class_dev->kobj, KOBJ_OFFLINE);
+ kfree(class_name);
+ }
+}
+
static ssize_t show_dev(struct class_device *class_dev, char *buf)
{
return print_dev_t(buf, class_dev->devt);
@@ -526,7 +568,6 @@ int class_device_add(struct class_device
struct class *parent_class = NULL;
struct class_device *parent_class_dev = NULL;
struct class_interface *class_intf;
- char *class_name = NULL;
int error = -EINVAL;

class_dev = class_device_get(class_dev);
@@ -593,22 +634,13 @@ int class_device_add(struct class_device
if (error)
goto out5;

- if (class_dev->dev) {
- class_name = make_class_name(class_dev->class->name,
- &class_dev->kobj);
- error = sysfs_create_link(&class_dev->kobj,
- &class_dev->dev->kobj, "device");
- if (error)
- goto out6;
- error = sysfs_create_link(&class_dev->dev->kobj, &class_dev->kobj,
- class_name);
- if (error)
- goto out7;
- }
+ error = class_device_add_dev(class_dev);
+ if (error)
+ goto out6;

error = class_device_add_groups(class_dev);
if (error)
- goto out8;
+ goto out7;

kobject_uevent(&class_dev->kobj, KOBJ_ADD);

@@ -623,12 +655,8 @@ int class_device_add(struct class_device

goto out1;

- out8:
- if (class_dev->dev)
- sysfs_remove_link(&class_dev->kobj, class_name);
out7:
- if (class_dev->dev)
- sysfs_remove_link(&class_dev->kobj, "device");
+ class_device_remove_dev(class_dev);
out6:
class_device_remove_attrs(class_dev);
out5:
@@ -644,7 +672,6 @@ int class_device_add(struct class_device
class_put(parent_class);
out1:
class_device_put(class_dev);
- kfree(class_name);
return error;
}

@@ -720,7 +747,6 @@ void class_device_del(struct class_devic
struct class *parent_class = class_dev->class;
struct class_device *parent_device = class_dev->parent;
struct class_interface *class_intf;
- char *class_name = NULL;

if (parent_class) {
down(&parent_class->sem);
@@ -731,12 +757,7 @@ void class_device_del(struct class_devic
up(&parent_class->sem);
}

- if (class_dev->dev) {
- class_name = make_class_name(class_dev->class->name,
- &class_dev->kobj);
- sysfs_remove_link(&class_dev->kobj, "device");
- sysfs_remove_link(&class_dev->dev->kobj, class_name);
- }
+ class_device_remove_dev(class_dev);
sysfs_remove_link(&class_dev->kobj, "subsystem");
class_device_remove_file(class_dev, &class_dev->uevent_attr);
if (class_dev->devt_attr)
@@ -749,7 +770,6 @@ void class_device_del(struct class_devic

class_device_put(parent_device);
class_put(parent_class);
- kfree(class_name);
}

void class_device_unregister(struct class_device *class_dev)
@@ -821,6 +841,27 @@ int class_device_rename(struct class_dev
return error;
}

+int class_device_update_dev(struct class_device *class_dev, struct device *dev)
+{
+ int error = 0;
+
+ class_dev = class_device_get(class_dev);
+ if (!class_dev)
+ return -EINVAL;
+
+ if (class_dev->dev != dev) {
+ class_device_remove_dev(class_dev);
+
+ class_dev->dev = dev;
+
+ error = class_device_add_dev(class_dev);
+ }
+
+ class_device_put(class_dev);
+
+ return error;
+}
+
struct class_device * class_device_get(struct class_device *class_dev)
{
if (class_dev)
@@ -911,6 +952,7 @@ EXPORT_SYMBOL_GPL(class_device_get);
EXPORT_SYMBOL_GPL(class_device_put);
EXPORT_SYMBOL_GPL(class_device_create);
EXPORT_SYMBOL_GPL(class_device_destroy);
+EXPORT_SYMBOL_GPL(class_device_update_dev);
EXPORT_SYMBOL_GPL(class_device_create_file);
EXPORT_SYMBOL_GPL(class_device_remove_file);
EXPORT_SYMBOL_GPL(class_device_create_bin_file);
diff --git a/include/linux/device.h b/include/linux/device.h
index 1e5f30d..d76072b 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -249,6 +249,7 @@ extern int class_device_add(struct class
extern void class_device_del(struct class_device *);

extern int class_device_rename(struct class_device *, char *);
+extern int class_device_update_dev(struct class_device *, struct device *);

extern struct class_device * class_device_get(struct class_device *);
extern void class_device_put(struct class_device *);
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