block: Introduce path_has_protocol() function

The bdrv_find_protocol() function returns NULL if an unknown protocol
name is given.  It returns the "file" protocol when the filename
contains no protocol at all.  This makes it difficult to distinguish
between paths which contain a protocol and those which do not.

Factor out a helper function that tests whether or not a filename has a
protocol.  The next patch makes use of this function.
Signed-off-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block.c

@@ -70,6 +70,39 @@ static BlockDriverState *bs_snapshots;
 /* If non-zero, use only whitelisted block drivers */
 static int use_bdrv_whitelist;
 
+#ifdef _WIN32
+static int is_windows_drive_prefix(const char *filename)
+{
+    return (((filename[0] >= 'a' && filename[0] <= 'z') ||
+             (filename[0] >= 'A' && filename[0] <= 'Z')) &&
+            filename[1] == ':');
+}
+
+int is_windows_drive(const char *filename)
+{
+    if (is_windows_drive_prefix(filename) &&
+        filename[2] == '\0')
+        return 1;
+    if (strstart(filename, "\\\\.\\", NULL) ||
+        strstart(filename, "//./", NULL))
+        return 1;
+    return 0;
+}
+#endif
+
+/* check if the path starts with "<protocol>:" */
+static int path_has_protocol(const char *path)
+{
+#ifdef _WIN32
+    if (is_windows_drive(path) ||
+        is_windows_drive_prefix(path)) {
+        return 0;
+    }
+#endif
+
+    return strchr(path, ':') != NULL;
+}
+
 int path_is_absolute(const char *path)
 {
     const char *p;
@@ -244,26 +277,6 @@ void get_tmp_filename(char *filename, int size)
 }
 #endif
 
-#ifdef _WIN32
-static int is_windows_drive_prefix(const char *filename)
-{
-    return (((filename[0] >= 'a' && filename[0] <= 'z') ||
-             (filename[0] >= 'A' && filename[0] <= 'Z')) &&
-            filename[1] == ':');
-}
-
-int is_windows_drive(const char *filename)
-{
-    if (is_windows_drive_prefix(filename) &&
-        filename[2] == '\0')
-        return 1;
-    if (strstart(filename, "\\\\.\\", NULL) ||
-        strstart(filename, "//./", NULL))
-        return 1;
-    return 0;
-}
-#endif
-
 /*
  * Detect host devices. By convention, /dev/cdrom[N] is always
  * recognized as a host CDROM.
@@ -307,16 +320,11 @@ BlockDriver *bdrv_find_protocol(const char *filename)
         return drv1;
     }
 
-#ifdef _WIN32
-     if (is_windows_drive(filename) ||
-         is_windows_drive_prefix(filename))
-         return bdrv_find_format("file");
-#endif
-
-    p = strchr(filename, ':');
-    if (!p) {
+    if (!path_has_protocol(filename)) {
         return bdrv_find_format("file");
     }
+    p = strchr(filename, ':');
+    assert(p != NULL);
     len = p - filename;
     if (len > sizeof(protocol) - 1)
         len = sizeof(protocol) - 1;