mctpd: add MCTP Interface D-Bus object

Create the MCTP interfaces D-Bus objects for the existing MCTP links at
`/xyz/openbmc_project/mctp1/interfaces/<name>`. When the MCTP links is
removed from/added to the system, the D-Bus object will also be
removed/added.

Then, create an au.com.CodeConstruct.MCTP.Interface1 D-Bus interface for MCTP
interface D-Bus objects. The D-Bus interface includes the `Role`
property which reports BMC roles in the MCTP link. The possible value of
`Role` are `BusOwner`, `Endpoint` and `Unknown`.

Because the BMC `Role` in the MCTP interface is fixed. The `Role`
property is changeable value but it can only be changed when the current
configured value is `Unknown`.

Ex:
```
$ busctl tree au.com.codeconstruct.MCTP1
`- /au
  `- /au/com
    `- /au/com/codeconstruct
      `- /au/com/codeconstruct/mctp1
        |- /au/com/codeconstruct/mctp1/interfaces
        | |- /au/com/codeconstruct/mctp1/interfaces/lo
        | `- /au/com/codeconstruct/mctp1/interfaces/mctpi2c3
        `- /au/com/codeconstruct/mctp1/networks
          `- /au/com/codeconstruct/mctp1/networks/1
            `- /au/com/codeconstruct/mctp1/networks/1/endpoints
              `- /au/com/codeconstruct/mctp1/networks/1/endpoints/8

$ busctl introspect au.com.codeconstruct.MCTP1 /au/com/codeconstruct/mctp1/interfaces/mctpi2c3
NAME                                 TYPE      SIGNATURE RESULT/VALUE FLAGS
au.com.CodeConstruct.MCTP.Interface1 interface -         -            -
.Role                                property  s         "Endpoint"   emits-change writable
org.freedesktop.DBus.Introspectable  interface -         -            -
.Introspect                          method    -         s            -
org.freedesktop.DBus.Peer            interface -         -            -
.GetMachineId                        method    -         s            -
.Ping                                method    -         -            -
org.freedesktop.DBus.Properties      interface -         -            -
.Get                                 method    ss        v            -
.GetAll                              method    s         a{sv}        -
.Set                                 method    ssv       -            -
.PropertiesChanged                   signal    sa{sv}as  -            -

$ busctl set-property au.com.codeconstruct.MCTP1 /au/com/codeconstruct/mctp1/interfaces/mctpi2c3 au.com.CodeConstruct.MCTP.Link1 Role s BusOwner

$ busctl get-property au.com.codeconstruct.MCTP1 /au/com/codeconstruct/mctp1/interfaces/mctpi2c3 au.com.CodeConstruct.MCTP.Link1 Role
s "BusOwner"
```

Includes minor changes from Jeremy Kerr <jk@codeconstruct.com.au>.

Signed-off-by: Thu Nguyen <thu@os.amperecomputing.com>
Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>

Author: ThuBaNguyen

CHANGELOG.md

@@ -14,6 +14,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 4. mctpd: Add AssignEndpointStatic for static EID allocations
 5. mctpd: New test infrastructure for control procotol messaging to mctpd
 6. mctpd: Add a configuration file facility, defaulting to /etc/mctpd.conf.
+7. mctpd: Add mctp/interfaces/<name> D-Bus object
 
 ### Changed
 

conf/mctpd.conf

@@ -1,4 +1,4 @@
-# Mode: either bus-owner or endpoint
+# Mode: either bus-owner or endpoint or unknown
 mode = "bus-owner"
 
 # MCTP protocol configuration. Used for both endpoint and bus-owner modes.

docs/mctpd.md

@@ -104,3 +104,17 @@ busctl call au.com.codeconstruct.MCTP1 \
 
 Removes the MCTP endpoint from `mctpd`, and deletes routes and neighbour entries.
 
+## D-Bus /au/com/codeconstruct/mctp1/interfaces/<name>
+
+`mctpd` provides a D-Bus path of `/au/com/codeconstruct/mctp1/interfaces`.
+For each known MCTP interfaces, `mctpd` will populate an D-Bus object
+`/au/com/codeconstruct/mctp1/interfaces/<name>`. The D-Bus objects have
+interface `au.com.CodeConstruct.MCTP.Interface1`.
+The D-Bus interface includes the `Role` property which reports BMC roles
+in the link. The possible value of `Role` are `BusOwner`, `Endpoint` and
+`Unknown`. The `Role` property is a changeable value but it can only be
+changed when the current configured value is `Unknown` because the BMC
+`Role` in the MCTP link is specific depend on the system.
+The D-Bus `/au/com/codeconstruct/mctp1/interfaces/<name>` objects also
+includes an au.com.codeconstruct.MCTP.BusOwner1 which exposes bus-owner
+level functions.

src/mctp-netlink.c

@@ -952,6 +952,19 @@ void *mctp_nl_get_link_userdata(const mctp_nl *nl, int ifindex)
 	return entry ? entry->userdata : NULL;
 }
 
+void *mctp_nl_get_link_userdata_byname(const mctp_nl *nl, const char *ifname)
+{
+       size_t i;
+
+       for (i = 0; i < nl->linkmap_count; i++) {
+               struct linkmap_entry *entry = &nl->linkmap[i];
+               if (!strcmp(entry->ifname, ifname))
+                       return entry->userdata;
+       }
+
+       return NULL;
+}
+
 bool mctp_nl_up_byindex(const mctp_nl *nl, int index)
 {
 	struct linkmap_entry *entry = entry_byindex(nl, index);

src/mctp-netlink.h

@@ -84,6 +84,8 @@ int mctp_nl_set_link_userdata(mctp_nl *nl, int ifindex, void *userdata);
 
 /* Returns NULL if the link does not exist */
 void *mctp_nl_get_link_userdata(const mctp_nl *nl, int ifindex);
+/* Returns NULL if the link does not exist */
+void *mctp_nl_get_link_userdata_byname(const mctp_nl *nl, const char *ifname);
 
 /* MCTP route helper */
 int mctp_nl_route_add(struct mctp_nl *nl, uint8_t eid, const char* ifname,