firewire: cdev: add PHY packet reception

Add an FW_CDEV_IOC_RECEIVE_PHY_PACKETS ioctl() and
FW_CDEV_EVENT_PHY_PACKET_RECEIVED poll()/read() event for /dev/fw*.
This can be used to get information from remote PHYs by remote access
PHY packets.

This is also the 2nd half of the functionality (the receive part) to
support a userspace implementation of a VersaPHY transaction layer.

Safety considerations:

  - PHY packets are generally broadcasts, hence some kind of elevated
    privileges should be required of a process to be able to listen in
    on PHY packets.  This implementation assumes that a process that is
    allowed to open the /dev/fw* of a local node does have this
    privilege.

    There was an inconclusive discussion about introducing POSIX
    capabilities as a means to check for user privileges for these
    kinds of operations.

Other limitations:

  - PHY packet reception may be switched on by ioctl() but cannot be
    switched off again.  It would be trivial to provide an off switch,
    but this is not worth the code.  The client should simply close()
    the fd then, or just ignore further events.

  - For sake of simplicity of API and kernel-side implementation, no
    filter per packet content is provided.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>

1 files changed, 2 insertions, 1 deletions

diff --git a/include/linux/firewire.h b/include/linux/firewire.h
index 0c38b8e97722..d974aa4a24c9 100644
--- a/include/linux/firewire.h
+++ b/include/linux/firewire.h
@@ -111,9 +111,10 @@ struct fw_card {
         bool beta_repeaters_present;
 
         int index;
-
         struct list_head link;
 
+        struct list_head phy_receiver_list;
+
         struct delayed_work br_work; /* bus reset job */
         bool br_short;