man/fi_domain: Define resource mgmt unreachable EP

Resource management unreachable EP addresses the issue of issuing RDMA
operations to a connectionless EP which cannot be reach. Such examples
include no-route-to-host or target NIC down. Defining this behavior is
important for storage use-cases where NICs may unexpectedly disappear.

Signed-off-by: Ian Ziemba <ian.ziemba@hpe.com>

man/fi_domain.3.md

@@ -413,17 +413,18 @@ the endpoint is reliable or unreliable, as well as provider and protocol
 specific implementation details, as shown in the following table.  The
 table assumes that all peers enable or disable RM the same.
 
-| Resource | DGRAM EP-no RM | DGRAM EP-with RM | RDM/MSG EP-no RM | RDM/MSG EP-with RM |
-|:--------:|:-------------------:|:-------------------:|:------------------:|:-----------------:|
-| Tx Ctx         | undefined error  | EAGAIN           | undefined error   | EAGAIN             |
-| Rx Ctx         | undefined error  | EAGAIN           | undefined error   | EAGAIN             |
-| Tx CQ          | undefined error  | EAGAIN           | undefined error   | EAGAIN             |
-| Rx CQ          | undefined error  | EAGAIN           | undefined error   | EAGAIN             |
-| Target EP      | dropped          | dropped          | transmit error    | retried            |
-| No Rx Buffer   | dropped          | dropped          | transmit error    | retried            |
-| Rx Buf Overrun | truncate or drop | truncate or drop | truncate or error | truncate or error  |
-| Unmatched RMA  | not applicable   | not applicable   | transmit error    | transmit error     |
-| RMA Overrun    | not applicable   | not applicable   | transmit error    | transmit error     |
+| Resource | DGRAM EP-no RM | DGRAM EP-with RM | MSG EP-no RM | MSG EP-with RM | RDM EP-no RM | RDM EP-with RM |
+|:--------:|:-------------------:|:-------------------:|:------------------:|:-----------------:| :------------------:|:-----------------:|
+| Tx Ctx         | undefined error  | EAGAIN           | undefined error   | EAGAIN             | undefined error   | EAGAIN             |
+| Rx Ctx         | undefined error  | EAGAIN           | undefined error   | EAGAIN             | undefined error   | EAGAIN             |
+| Tx CQ          | undefined error  | EAGAIN           | undefined error   | EAGAIN             | undefined error   | EAGAIN             |
+| Rx CQ          | undefined error  | EAGAIN           | undefined error   | EAGAIN             | undefined error   | EAGAIN             |
+| Target EP      | dropped          | dropped          | transmit error    | retried            | transmit error    | retried            |
+| No Rx Buffer   | dropped          | dropped          | transmit error    | retried            | transmit error    | retried            |
+| Rx Buf Overrun | truncate or drop | truncate or drop | truncate or error | truncate or error  | truncate or error | truncate or error  |
+| Unmatched RMA  | not applicable   | not applicable   | transmit error    | transmit error     | transmit error    | transmit error     |
+| RMA Overrun    | not applicable   | not applicable   | transmit error    | transmit error     | transmit error    | transmit error     |
+| Unreachable EP | dropped          | dropped          | not applicable    | not applicable     | transmit error    | transmit error     |
 
 The resource column indicates the resource being accessed by a data
 transfer operation.
@@ -482,19 +483,28 @@ transfer operation.
   operations, or attempt to access outside of the target memory region
   will fail, resulting in a transmit error.
 
+*Unreachable EP*
+: Unreachable endpoint is a connectionless specific scenario where transmit
+  operations are issued to unreachable target endpoints. Such scenarios include
+  no-route-to-host or down target NIC. For FI_EP_DGRAM endpoints, transmit
+  operations targeting an unreachable endpoint will have operation dropped. For
+  FI_EP_RDM, target operations targeting an unreachable endpoint will result in
+  a transmit error. A provider may choose to set the completion error code to
+  FI_EHOSTUNREACH signaling to user the target endpoint is unreachable.
+
 When a resource management error occurs on an connected endpoint, the endpoint
 will transition into a disabled state and the connection torn down. While
 transitioning to disabled, any queued and inflight operations will be dropped.
 Connection must be re-established for endpoint to be usable.
 
 When a resource management error occurs on an connectionless endpoint, Target
-EP, No Rx Buffer, Rx Buf Overrun, Unmatched RMA, and RMA Overrun errors will not
-result in endpoint transitioning into a disabled state. Tx Ctx, Rx Ctx, Tx CQ,
-and Rx CQ errors will transition the endpoint into a disabled state. While
-transitioning to disabled, any queued and inflight, local transmit operations
-will be dropped. Endpoints targeting a disabled EP must adhere to the Target EP
-behavior. If the endpoint becomes disabled, the endpoint must be re-enabled
-before it will accept new data transfer operations.
+EP, No Rx Buffer, Rx Buf Overrun, Unmatched RMA, RMA Overrun, and Unreachable EP
+errors will not result in endpoint transitioning into a disabled state. Tx Ctx,
+Rx Ctx, Tx CQ, and Rx CQ errors will transition the endpoint into a disabled
+state. While transitioning to disabled, any queued and inflight, local transmit
+operations will be dropped. Endpoints targeting a disabled EP must adhere to the
+Target EP behavior. If the endpoint becomes disabled, the endpoint must be
+re-enabled before it will accept new data transfer operations.
 
 There is one notable restriction on the protections offered by resource
 management.  This occurs when resource management is enabled on an