[PATCH for-7.2 v2 16/20] device_tree.c: support string props in fdt_format_node()

[Daniel Henrique Barboza <danielhb413@gmail.com>]

To support printing string properties in 'info fdt' we need to determine
whether a void data might contain a string.

We do that by casting the void data to a string array and:

- check if the array finishes with a null character
- check if all characters are printable

If both conditions are met, we'll consider it to be a string data type
and print it accordingly. After this change, 'info fdt' is now able to
print string properties. Here's an example with the ARM 'virt' machine:

(qemu) info fdt /chosen
chosen {
    stdout-path = '/pl011@9000000'
    rng-seed;
    kaslr-seed;
}

Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
---
 softmmu/device_tree.c | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/softmmu/device_tree.c b/softmmu/device_tree.c
index 3fb07b537f..8691c3ccc0 100644
--- a/softmmu/device_tree.c
+++ b/softmmu/device_tree.c
@@ -663,6 +663,24 @@ void qemu_fdt_qmp_dumpdtb(const char *filename, Error **errp)
     error_setg(errp, "Error when saving machine FDT to file %s", filename);
 }
 
+static bool fdt_prop_is_string(const void *data, int size)
+{
+    const char *str = data;
+    int i;
+
+    if (size <= 0 || str[size - 1] != '\0') {
+        return false;
+    }
+
+    for (i = 0; i < size - 1; i++) {
+        if (!g_ascii_isprint(str[i])) {
+            return false;
+        }
+    }
+
+    return true;
+}
+
 static void fdt_format_node(GString *buf, int node, int depth)
 {
     const struct fdt_property *prop = NULL;
@@ -681,7 +699,12 @@ static void fdt_format_node(GString *buf, int node, int depth)
         prop = fdt_get_property_by_offset(fdt, property, &prop_size);
         propname = fdt_string(fdt, fdt32_to_cpu(prop->nameoff));
 
-        g_string_append_printf(buf, "%*s%s;\n", padding, "", propname);
+        if (fdt_prop_is_string(prop->data, prop_size)) {
+            g_string_append_printf(buf, "%*s%s = '%s'\n",
+                                   padding, "", propname, prop->data);
+        } else {
+            g_string_append_printf(buf, "%*s%s;\n", padding, "", propname);
+        }
     }
 
     padding -= 4;
-- 
2.36.1