Several sub-modules like HIDP, rfcomm, ... need to track l2cap
connections. The l2cap_conn->hcon->dev object is used as parent for sysfs
devices so the sub-modules need to be notified when the hci_conn object is
removed from sysfs.
As submodules normally use the l2cap layer, the l2cap_user objects are
registered there instead of on the underlying hci_conn object. This avoids
any direct dependency on the HCI layer and lets the l2cap core handle any
specifics.
This patch introduces l2cap_user objects which contain a "probe" and
"remove" callback. You can register them on any l2cap_conn object and if
it is active, the "probe" callback will get called. Otherwise, an error is
returned.
The l2cap_conn object will call your "remove" callback directly before it
is removed from user-space. This allows you to remove your submodules
_before_ the parent l2cap_conn and hci_conn object is removed.
At any time you can asynchronously unregister your l2cap_user object if
your submodule vanishes before the l2cap_conn object does.
There is no way around l2cap_user. If we want wire-protocols in the
kernel, we always want the hci_conn object as parent in the sysfs tree. We
cannot use a channel here since we might need multiple channels for a
single protocol.
But the problem is, we _must_ get notified when an l2cap_conn object is
removed. We cannot use reference-counting for object-removal! This is not
how it works. If a hardware is removed, we should immediately remove the
object from sysfs. Any other behavior would be inconsistent with the rest
of the system. Also note that device_del() might sleep, but it doesn't
wait for user-space or block very long. It only _unlinks_ the object from
sysfs and the whole device-tree. Everything else is handled by ref-counts!
This is exactly what the other sub-modules must do: unlink their devices
when the "remove" l2cap_user callback is called. They should not do any
cleanup or synchronous shutdowns.
Signed-off-by: David Herrmann <dh.herrmann@xxxxxxxxx>
Acked-by: Marcel Holtmann <marcel@xxxxxxxxxxxx>
---
include/net/bluetooth/l2cap.h | 10 +++++
net/bluetooth/l2cap_core.c | 86 +++++++++++++++++++++++++++++++++++++++++++
2 files changed, 96 insertions(+)
diff --git a/include/net/bluetooth/l2cap.h b/include/net/bluetooth/l2cap.h
index 7b4cc5b..fb94cf1 100644
--- a/include/net/bluetooth/l2cap.h
+++ b/include/net/bluetooth/l2cap.h
@@ -584,6 +584,13 @@ struct l2cap_conn {
struct list_head chan_l;
struct mutex chan_lock;
struct kref ref;
+ struct list_head users;
+};
+
+struct l2cap_user {
+ struct list_head list;
+ int (*probe) (struct l2cap_conn *conn, struct l2cap_user *user);
+ void (*remove) (struct l2cap_conn *conn, struct l2cap_user *user);
};
#define L2CAP_INFO_CL_MTU_REQ_SENT 0x01
@@ -817,4 +824,7 @@ void __l2cap_physical_cfm(struct l2cap_chan *chan, int result);
void l2cap_conn_get(struct l2cap_conn *conn);
void l2cap_conn_put(struct l2cap_conn *conn);
+int l2cap_register_user(struct l2cap_conn *conn, struct l2cap_user *user);
+void l2cap_unregister_user(struct l2cap_conn *conn, struct l2cap_user *user);
+
#endif /* __L2CAP_H */
diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index 5f273a3..e7c06d1 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -1446,6 +1446,89 @@ static void l2cap_info_timeout(struct work_struct *work)
l2cap_conn_start(conn);
}
+/*
+ * l2cap_user
+ * External modules can register l2cap_user objects on l2cap_conn. The ->probe
+ * callback is called during registration. The ->remove callback is called
+ * during unregistration.
+ * An l2cap_user object can either be explicitly unregistered or when the
+ * underlying l2cap_conn object is deleted. This guarantees that l2cap->hcon,
+ * l2cap->hchan, .. are valid as long as the remove callback hasn't been called.
+ * External modules must own a reference to the l2cap_conn object if they intend
+ * to call l2cap_unregister_user(). The l2cap_conn object might get destroyed at
+ * any time if they don't.
+ */
+
+int l2cap_register_user(struct l2cap_conn *conn, struct l2cap_user *user)
+{
+ struct hci_dev *hdev = conn->hcon->hdev;
+ int ret;
+
+ /* We need to check whether l2cap_conn is registered. If it is not, we
+ * must not register the l2cap_user. l2cap_conn_del() is unregisters
+ * l2cap_conn objects, but doesn't provide its own locking. Instead, it
+ * relies on the parent hci_conn object to be locked. This itself relies
+ * on the hci_dev object to be locked. So we must lock the hci device
+ * here, too. */
+
+ hci_dev_lock(hdev);
+
+ if (user->list.next || user->list.prev) {
+ ret = -EINVAL;
+ goto out_unlock;
+ }
+
+ /* conn->hchan is NULL after l2cap_conn_del() was called */
+ if (!conn->hchan) {
+ ret = -ENODEV;
+ goto out_unlock;
+ }
+
+ ret = user->probe(conn, user);
+ if (ret)
+ goto out_unlock;
+
+ list_add(&user->list, &conn->users);
+ ret = 0;
+
+out_unlock:
+ hci_dev_unlock(hdev);
+ return ret;
+}
+EXPORT_SYMBOL(l2cap_register_user);
+
+void l2cap_unregister_user(struct l2cap_conn *conn, struct l2cap_user *user)
+{
+ struct hci_dev *hdev = conn->hcon->hdev;
+
+ hci_dev_lock(hdev);
+
+ if (!user->list.next || !user->list.prev)
+ goto out_unlock;
+
+ list_del(&user->list);
+ user->list.next = NULL;
+ user->list.prev = NULL;
+ user->remove(conn, user);
+
+out_unlock:
+ hci_dev_unlock(hdev);
+}
+EXPORT_SYMBOL(l2cap_unregister_user);
+
+static void l2cap_unregister_all_users(struct l2cap_conn *conn)
+{
+ struct l2cap_user *user;
+
+ while (!list_empty(&conn->users)) {
+ user = list_first_entry(&conn->users, struct l2cap_user, list);
+ list_del(&user->list);
+ user->list.next = NULL;
+ user->list.prev = NULL;
+ user->remove(conn, user);
+ }
+}
+
static void l2cap_conn_del(struct hci_conn *hcon, int err)
{
struct l2cap_conn *conn = hcon->l2cap_data;
@@ -1458,6 +1541,8 @@ static void l2cap_conn_del(struct hci_conn *hcon, int err)
kfree_skb(conn->rx_skb);
+ l2cap_unregister_all_users(conn);
+
mutex_lock(&conn->chan_lock);
/* Kill channels */
@@ -1550,6 +1635,7 @@ static struct l2cap_conn *l2cap_conn_add(struct hci_conn *hcon, u8 status)
mutex_init(&conn->chan_lock);
INIT_LIST_HEAD(&conn->chan_l);
+ INIT_LIST_HEAD(&conn->users);
if (hcon->type == LE_LINK)
INIT_DELAYED_WORK(&conn->security_timer, security_timeout);
--
1.8.2
--
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