firewire: fix use of multiple AV/C devices, allow multiple FCP listeners

Control of more than one AV/C device at once --- e.g. camcorders, tape
decks, audio devices, TV tuners --- failed or worked only unreliably,
depending on driver implementation.  This affected kernelspace and
userspace drivers alike and was caused by firewire-core's inability to
accept multiple registrations of FCP listeners.

The fix allows multiple address handlers to be registered for the FCP
command and response registers.  When a request for these registers is
received, all handlers are invoked, and the Firewire response is
generated by the core and not by any handler.

The cdev API does not change, i.e., userspace is still expected to send
a response for FCP requests; this response is silently ignored.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de> (changelog, rebased, whitespace)

1 files changed, 15 insertions, 11 deletions

diff --git a/drivers/firewire/core-cdev.c b/drivers/firewire/core-cdev.c
index 231e6ee5ba43..2cb22d160f6e 100644
--- a/drivers/firewire/core-cdev.c
+++ b/drivers/firewire/core-cdev.c
@@ -601,8 +601,9 @@ static void release_request(struct client *client,
         struct inbound_transaction_resource *r = container_of(resource,
                         struct inbound_transaction_resource, resource);
 
-        fw_send_response(client->device->card, r->request,
-                         RCODE_CONFLICT_ERROR);
+        if (r->request)
+                fw_send_response(client->device->card, r->request,
+                                 RCODE_CONFLICT_ERROR);
         kfree(r);
 }
 
@@ -645,7 +646,8 @@ static void handle_request(struct fw_card *card, struct fw_request *request,
  failed:
         kfree(r);
         kfree(e);
-        fw_send_response(card, request, RCODE_CONFLICT_ERROR);
+        if (request)
+                fw_send_response(card, request, RCODE_CONFLICT_ERROR);
 }
 
 static void release_address_handler(struct client *client,
@@ -715,15 +717,17 @@ static int ioctl_send_response(struct client *client, void *buffer)
 
         r = container_of(resource, struct inbound_transaction_resource,
                          resource);
-        if (request->length < r->length)
-                r->length = request->length;
-
-        if (copy_from_user(r->data, u64_to_uptr(request->data), r->length)) {
-                ret = -EFAULT;
-                goto out;
+        if (r->request) {
+                if (request->length < r->length)
+                        r->length = request->length;
+                if (copy_from_user(r->data, u64_to_uptr(request->data),
+                                   r->length)) {
+                        ret = -EFAULT;
+                        goto out;
+                }
+                fw_send_response(client->device->card, r->request,
+                                 request->rcode);
         }
-
-        fw_send_response(client->device->card, r->request, request->rcode);
  out:
         kfree(r);