kernel-device: new helper to load lower device link names

Based exclusively on sysfs for now. We could do this via netlink if
needed as well.

3 files changed, 90 insertions, 0 deletions

diff --git a/src/Makefile.am b/src/Makefile.am
index 24ef8bb8..120503e1 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -149,6 +149,8 @@ libkerneldevice_la_CPPFLAGS = \
 libkerneldevice_la_SOURCES = \
 	kerneldevice/mm-kernel-device.h \
 	kerneldevice/mm-kernel-device.c \
+	kerneldevice/mm-kernel-device-helpers.h \
+	kerneldevice/mm-kernel-device-helpers.c \
 	kerneldevice/mm-kernel-device-generic.h \
 	kerneldevice/mm-kernel-device-generic.c \
 	kerneldevice/mm-kernel-device-generic-rules.h \
diff --git a/src/kerneldevice/mm-kernel-device-helpers.c b/src/kerneldevice/mm-kernel-device-helpers.c
new file mode 100644
index 00000000..d9bcfd97
--- /dev/null
+++ b/src/kerneldevice/mm-kernel-device-helpers.c
@@ -0,0 +1,62 @@
+/* -*- Mode: C; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details:
+ *
+ * Copyright (C) 2021 Aleksander Morgado <aleksander@aleksander.es>
+ */
+
+#include <stdlib.h>
+
+#include <glib.h>
+#include <glib-object.h>
+#include <gio/gio.h>
+
+#include "mm-kernel-device-helpers.h"
+
+gchar *
+mm_kernel_device_get_lower_device_name (const gchar *sysfs_path)
+{
+    g_autoptr(GFile)           dirfile = NULL;
+    g_autoptr(GFileEnumerator) direnum = NULL;
+
+    dirfile = g_file_new_for_path (sysfs_path);
+    direnum = g_file_enumerate_children (dirfile,
+                                         G_FILE_ATTRIBUTE_STANDARD_NAME,
+                                         G_FILE_QUERY_INFO_NONE,
+                                         NULL,
+                                         NULL);
+    if (!direnum)
+        return NULL;
+
+    while (TRUE) {
+        GFileInfo        *info;
+        g_autofree gchar *filename = NULL;
+        g_autofree gchar *link_path = NULL;
+        g_autofree gchar *real_path = NULL;
+        g_autofree gchar *basename = NULL;
+
+        if (!g_file_enumerator_iterate (direnum, &info, NULL, NULL, NULL) || !info)
+            break;
+
+        filename = g_file_info_get_attribute_as_string (info, G_FILE_ATTRIBUTE_STANDARD_NAME);
+        if (!filename || !g_str_has_prefix (filename, "lower_"))
+            continue;
+
+        link_path = g_strdup_printf ("%s/%s", sysfs_path, filename);
+        real_path = realpath (link_path, NULL);
+        if (!real_path)
+            continue;
+
+        return g_path_get_basename (real_path);
+    }
+
+    return NULL;
+}
diff --git a/src/kerneldevice/mm-kernel-device-helpers.h b/src/kerneldevice/mm-kernel-device-helpers.h
new file mode 100644
index 00000000..48a86233
--- /dev/null
+++ b/src/kerneldevice/mm-kernel-device-helpers.h
@@ -0,0 +1,26 @@
+/* -*- Mode: C; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details:
+ *
+ * Copyright (C) 2021 Aleksander Morgado <aleksander@aleksander.es>
+ */
+
+#ifndef MM_KERNEL_DEVICE_HELPERS_H
+#define MM_KERNEL_DEVICE_HELPERS_H
+
+#include <glib.h>
+
+/* For virtual devices that keep a "lower" link to the parent physical device
+ * they're based on, get the name of that parent physical device.
+ * (e.g. lower_device_name(qmimux0) == wwan0) */
+gchar *mm_kernel_device_get_lower_device_name (const gchar *sysfs_path);
+
+#endif /* MM_KERNEL_DEVICE_HERLPERS_H */