Add facility for link-specific role configuration

CHANGELOG.md

@@ -11,11 +11,22 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 1. `mctpd` now queries endpoints for their vendor-defined message support,
    and publishes as the newly-specced `VendorDefinedMessageTypes` dbus property.
 
+2. `mctpd` now supports configuration on individual links, without having
+   to perform dbus property updates. Links may be matched on physical transport
+   binding type, or by sysfs paths, allowing individual interface roles to be
+   specified by the configuration file.
+
 ### Fixes
 
 1. mctpd's interface objects now expose the BusOwner1 interface when set
    as a BusOwner via the Role property
 
+### Changed
+
+1. `mctpd`'s `mode` configuration (setting bus owner vs. endpoint roles) is
+   now called `role`. Configuration parsing will still allow the `mode` setting,
+   but this will be deprecated in a later release.
+
 ## [2.5] - 2026-02-17
 
 ### Added

conf/mctpd.conf

@@ -1,5 +1,5 @@
-# Mode: either bus-owner or endpoint or unknown
-mode = "bus-owner"
+# Role: either bus-owner or endpoint or unknown
+role = "bus-owner"
 
 # MCTP protocol configuration. Used for both endpoint and bus-owner modes.
 [mctp]

docs/mctpd.md

@@ -315,17 +315,24 @@ The configuration file has a global section, plus function-specific sections.
 
 These apply to all modes of `mctpd` operation. One top-level setting is defined:
 
-#### `mode`: mctpd mode of operation
+#### `role`: local MCTP device role
 
-* type: string enum: `bus-owner` or `endpoint`
+* type: string enum: `bus-owner`, `endpoint` or `unknown`
 * default: `bus-owner`
 
-This sets the overall mode of `mctpd`, either as a Bus Owner (`mode =
-"bus-owner"`) or Endpoint (`mode = "endpoint"`). In bus owner mode, mctpd will
+This sets the overall role of `mctpd`, either as a Bus Owner (`role =
+"bus-owner"`) or Endpoint (`role = "endpoint"`). In bus owner mode, mctpd will
 assume responsibility for allocating addresses to other endpoints. In endpoint
 mode, mctpd will not allocate addresses, but instead accept allocations from an
 external bus owner.
 
+A value of `unknown` allows per-interface settings; the dbus interface's
+`au.com.codeconstruct.MCTP.Interface1.Role` property may be written to set
+a specific role for each interface.
+
+Previous versions of `mctpd` used `mode` for this configuration, both `role`
+and `mode` are accepted.
+
 ### `[mctp]` section
 
 This section affects MCTP protocol behaviour, and any common values used for
@@ -398,3 +405,62 @@ space. Value should be between [```0.5 * TRECLAIM (5)```- ```10```] seconds.
 Such periodic polling is common for all the briged endpoints among allocated
 pool space [`.PoolStart` - `.PoolEnd`] of the bridge.
 Polling could be provisioned to be disabled via setting the value as ```0```.
+
+### `[[interface]]`: per-interface configuration
+
+The `[[interface]]` table allows configuration to be applied to specific
+interfaces. Each `[[interface]]` entry contains a "match" definition, which
+determines which MCTP interfaces the table applies to.
+
+Matches are processed in the order they appear in the configuration file;
+the first `[[interface]]` section that matches is applied.
+
+Other content of the interface table is configuration to be applied. The
+only setting currently supported is `role`, to set mctpd's role as
+either bus-owner or endpoint on this interface.
+
+```toml
+role = "bus-owner"
+[[interface]]
+match = ...
+role = "endpoint"
+```
+
+#### Match types
+
+Match on all interfaces:
+
+```toml
+# match all interfaces
+[[interface]]
+match = "all"
+```
+
+Match on a physical transport binding type:
+
+```toml
+# match only MCTP-over-i2c interfaces
+[[interface]]
+match = { phys-type = "i2c" }
+```
+
+Available binding types are: `SMBus` / `I2C`, `PCIe`, `USB`, `KCS`, `serial`,
+`I3C`, `MMBI`, or `UCIE`. Matches are case-insensitive.
+
+Match on a sysfs device path:
+
+```toml
+# match on sysfs path
+[[interface]]
+match = { path = "/devices/pci0000:00/0000:00:08.3/usb10/10-0:1.0" }
+```
+
+Paths may use glob expressions:
+
+```toml
+# match on globbed sysfs path
+[[interface]]
+match = { path = "/devices/pci0000:00/0000:00:08.3/*" }
+```
+
+Paths have the `/sys` prefix stripped.

src/mctp-ops.c

@@ -7,6 +7,9 @@
 
 #define _GNU_SOURCE
 
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
 #include <unistd.h>
 #include <linux/netlink.h>
 #include <err.h>
@@ -52,6 +55,36 @@ static int mctp_op_close(int sd)
 	return close(sd);
 }
 
+static int mctp_op_link_sysfs_path(const char *ifname, char **path)
+{
+	char *dev_class_path = NULL, *dev_path = NULL;
+	int rc = 1;
+
+	rc = asprintf(&dev_class_path, "/sys/class/net/%s/device", ifname);
+	if (rc < 0)
+		return -1;
+
+	dev_path = realpath(dev_class_path, NULL);
+	if (!dev_path) {
+		warnx("no path data for interface %s", ifname);
+		goto out;
+	}
+
+	if (!strncmp(dev_path, "/sys", strlen("/sys"))) {
+		warnx("malformed interface path for %s", ifname);
+		goto out;
+	}
+
+	*path = strdup(dev_path + 4);
+	rc = 0;
+
+out:
+	free(dev_path);
+	free(dev_class_path);
+	return rc;
+	return -1;
+}
+
 static void mctp_bug_warn(const char *fmt, va_list args)
 {
 	vwarnx(fmt, args);
@@ -81,6 +114,7 @@ const struct mctp_ops mctp_ops = {
 	},
 #endif
 	.bug_warn = mctp_bug_warn,
+	.link_sysfs_path = mctp_op_link_sysfs_path,
 };
 
 void mctp_ops_init(void)

src/mctp-ops.h

@@ -41,6 +41,7 @@ struct mctp_ops {
 	struct sd_event_ops sd_event;
 #endif
 	void (*bug_warn)(const char *fmt, va_list args);
+	int (*link_sysfs_path)(const char *ifname, char **devpath);
 };
 
 extern const struct mctp_ops mctp_ops;