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+D-Bus Method Return Error Codes
+===============================
+
+The motivation of having detailed error is to provide context-based failure
+reasons along with D-Bus method return so that D-Bus clients can build metrics
+and optimize their application based on these failure reasons. For instance, a
+client can build retry mechanism for a connection failure or improve the
+bottleneck of use scenario based on actionable metrics.
+
+These error codes are context-based but not necessarily tied to interface or
+method calls. For instance, if a pairing request failed due to connection
+failure, connection error would be attached to the method return of Pair().
+
+BR/EDR connection already connected
+===================================
+ errno: EALREADY, EISCONN
+
+ Either the profile is already connected or ACL connection is in place.
+
+BR/EDR connection page timeout
+==============================
+ errno: EHOSTDOWN
+
+ Failed due to page timeout.
+
+BR/EDR connection profile unavailable
+=====================================
+ errno: ENOPROTOOPT
+
+ Failed to find connectable services or the target service.
+
+BR/EDR connection SDP search
+============================
+ errno: none
+
+ Failed to complete the SDP search.
+
+BR/EDR connection create socket
+===============================
+ errno: EIO
+
+ Failed to create or connect to BT IO socket. This can also indicate
+ hardware failure in the controller.
+
+BR/EDR connection invalid arguments
+===================================
+ errno: EHOSTUNREACH
+
+ Failed due to invalid arguments.
+
+BR/EDR connection not powered
+=============================
+ errno: EHOSTUNREACH
+
+ Failed due to adapter not powered.
+
+BR/EDR connection not supported
+===============================
+ errno: EOPNOTSUPP, EPROTONOSUPPORT
+
+ Failed due to unsupported state transition of L2CAP channel or other
+ features either by the local host or the remote.
+
+BR/EDR connection bad socket
+============================
+ errno: EBADFD
+
+ Failed due to the socket is in bad state.
+
+BR/EDR connection memory allocation
+===================================
+ errno: ENOMEM
+
+ Failed to allocate memory in either host stack or controller.
+
+BR/EDR connection busy
+======================
+ errno: EBUSY
+
+ Failed due to other ongoing operations, such as pairing, busy L2CAP
+ channel or the operation disallowed by the controller.
+
+BR/EDR connection concurrent connection limit
+=============================================
+ errno: EMLINK
+
+ Failed due to reaching the concurrent connection limit to a device.
+
+BR/EDR connection timeout
+=========================
+ errno: ETIMEDOUT
+
+ Failed due to connection timeout
+
+BR/EDR connection refused
+=========================
+ errno: ECONNREFUSED
+
+ Refused by the remote device due to limited resource, security reason
+ or unacceptable address type.
+
+BR/EDR connection aborted by remote
+===================================
+ errno: ECONNRESET
+
+ Terminated by the remote device due to limited resource or power off.
+
+BR/EDR connection aborted by local
+==================================
+ errno: ECONNABORTED
+
+ Aborted by the local host.
+
+BR/EDR connection LMP protocol error
+====================================
+ errno: EPROTO
+
+ Failed due to LMP protocol error.
+
+BR/EDR connection canceled
+==========================
+ errno: none
+
+ Failed due to cancellation caused by adapter drop, unexpected device
+ drop, orincoming disconnection request before connection request is
+ completed.
+
+BR/EDR connection unknown error
+===============================
+ errno: ENOSYS
+
+ Failed due to unknown reason.
+
+LE connection invalid arguments
+===============================
+ errno: EINVAL
+
+ Failed due to invalid arguments.
+
+LE connection not powered
+=========================
+ errno: EHOSTUNREACH
+
+ Failed due to adapter not powered.
+
+LE connection not supported
+===========================
+ errno: EOPNOTSUPP, EPROTONOSUPPORT
+
+ Failed due to unsupported state transition of L2CAP channel or other
+ features (e.g. LE features) either by the local host or the remote.
+
+LE connection already connected
+===============================
+ errno: EALREADY, EISCONN
+
+ Either the BT IO is already connected or LE link connection in place.
+
+LE connection bad socket
+========================
+ errno: EBADFD
+
+ Failed due to the socket is in bad state.
+
+LE connection memory allocation
+===============================
+ errno: ENOMEM
+
+ Failed to allocate memory in either host stack or controller.
+
+LE connection busy
+==================
+ errno: EBUSY
+
+ Failed due to other ongoing operations, such as pairing, connecting,
+ busy L2CAP channel or the operation disallowed by the controller.
+
+LE connection refused
+=====================
+ errno: ECONNREFUSED
+
+ Failed due to that LE is not enabled or the attempt is refused by the
+ remote device due to limited resource, security reason or unacceptable
+ address type.
+
+LE connection create socket
+===========================
+ errno: EIO
+
+ Failed to create or connect to BT IO socket. This can also indicate
+ hardware failure in the controller.
+
+LE connection timeout
+=====================
+ errno: ETIMEDOUT
+
+ Failed due to connection timeout
+
+LE connection concurrent connection limit
+=========================================
+ errno: EMLINK
+
+ Failed due to reaching the synchronous connection limit to a device.
+
+LE connection abort by remote
+=============================
+ errno: ECONNRESET
+
+ Aborted by the remote device due to limited resource or power off.
+
+LE connection abort by local
+============================
+ errno: ECONNABORTED
+
+ Aborted by the local host.
+
+LE connection link layer protocol error
+=======================================
+ errno: EPROTO
+
+ Failed due to link layer protocol error.
+
+LE connection GATT browsing
+===========================
+ errno: none
+
+ Failed to complete the GATT browsing.
+
+LE connection unknown error
+===========================
+ errno: ENOSYS
+
+ Failed due to unknown reason.