device_tree: introduce load_device_tree_from_sysfs

This function returns the host device tree blob from sysfs
(/proc/device-tree). It uses a recursive function inspired
from dtc read_fstree.

Signed-off-by: Eric Auger <eric.auger@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

device_tree.c

@@ -13,6 +13,10 @@
 
 #include "qemu/osdep.h"
 
+#ifdef CONFIG_LINUX
+#include <dirent.h>
+#endif
+
 #include "qemu-common.h"
 #include "qemu/error-report.h"
 #include "sysemu/device_tree.h"
@@ -112,6 +116,102 @@ void *load_device_tree(const char *filename_path, int *sizep)
     return NULL;
 }
 
+#ifdef CONFIG_LINUX
+
+#define SYSFS_DT_BASEDIR "/proc/device-tree"
+
+/**
+ * read_fstree: this function is inspired from dtc read_fstree
+ * @fdt: preallocated fdt blob buffer, to be populated
+ * @dirname: directory to scan under SYSFS_DT_BASEDIR
+ * the search is recursive and the tree is searched down to the
+ * leaves (property files).
+ *
+ * the function asserts in case of error
+ */
+static void read_fstree(void *fdt, const char *dirname)
+{
+    DIR *d;
+    struct dirent *de;
+    struct stat st;
+    const char *root_dir = SYSFS_DT_BASEDIR;
+    const char *parent_node;
+
+    if (strstr(dirname, root_dir) != dirname) {
+        error_setg(&error_fatal, "%s: %s must be searched within %s",
+                   __func__, dirname, root_dir);
+    }
+    parent_node = &dirname[strlen(SYSFS_DT_BASEDIR)];
+
+    d = opendir(dirname);
+    if (!d) {
+        error_setg(&error_fatal, "%s cannot open %s", __func__, dirname);
+    }
+
+    while ((de = readdir(d)) != NULL) {
+        char *tmpnam;
+
+        if (!g_strcmp0(de->d_name, ".")
+            || !g_strcmp0(de->d_name, "..")) {
+            continue;
+        }
+
+        tmpnam = g_strdup_printf("%s/%s", dirname, de->d_name);
+
+        if (lstat(tmpnam, &st) < 0) {
+            error_setg(&error_fatal, "%s cannot lstat %s", __func__, tmpnam);
+        }
+
+        if (S_ISREG(st.st_mode)) {
+            gchar *val;
+            gsize len;
+
+            if (!g_file_get_contents(tmpnam, &val, &len, NULL)) {
+                error_setg(&error_fatal, "%s not able to extract info from %s",
+                           __func__, tmpnam);
+            }
+
+            if (strlen(parent_node) > 0) {
+                qemu_fdt_setprop(fdt, parent_node,
+                                 de->d_name, val, len);
+            } else {
+                qemu_fdt_setprop(fdt, "/", de->d_name, val, len);
+            }
+            g_free(val);
+        } else if (S_ISDIR(st.st_mode)) {
+            char *node_name;
+
+            node_name = g_strdup_printf("%s/%s",
+                                        parent_node, de->d_name);
+            qemu_fdt_add_subnode(fdt, node_name);
+            g_free(node_name);
+            read_fstree(fdt, tmpnam);
+        }
+
+        g_free(tmpnam);
+    }
+
+    closedir(d);
+}
+
+/* load_device_tree_from_sysfs: extract the dt blob from host sysfs */
+void *load_device_tree_from_sysfs(void)
+{
+    void *host_fdt;
+    int host_fdt_size;
+
+    host_fdt = create_device_tree(&host_fdt_size);
+    read_fstree(host_fdt, SYSFS_DT_BASEDIR);
+    if (fdt_check_header(host_fdt)) {
+        error_setg(&error_fatal,
+                   "%s host device tree extracted into memory is invalid",
+                   __func__);
+    }
+    return host_fdt;
+}
+
+#endif /* CONFIG_LINUX */
+
 static int findnode_nofail(void *fdt, const char *node_path)
 {
     int offset;

include/sysemu/device_tree.h

@@ -16,6 +16,14 @@
 
 void *create_device_tree(int *sizep);
 void *load_device_tree(const char *filename_path, int *sizep);
+#ifdef CONFIG_LINUX
+/**
+ * load_device_tree_from_sysfs: reads the device tree information in the
+ * /proc/device-tree directory and return the corresponding binary blob
+ * buffer pointer. Asserts in case of error.
+ */
+void *load_device_tree_from_sysfs(void);
+#endif
 
 int qemu_fdt_setprop(void *fdt, const char *node_path,
                      const char *property, const void *val, int size);