block: allow filenames with colons again for host devices

Before the raw/file split we used to allow filenames with colons for host
device only.  While this was more by accident than by design people rely
on it, so we need to bring it back.

So move the host device probing to be before the protocol detection
again.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block.c

@@ -288,23 +288,30 @@ BlockDriver *bdrv_find_protocol(const char *filename)
     char protocol[128];
     int len;
     const char *p;
-    int is_drive;
 
     /* TODO Drivers without bdrv_file_open must be specified explicitly */
 
+    /*
+     * XXX(hch): we really should not let host device detection
+     * override an explicit protocol specification, but moving this
+     * later breaks access to device names with colons in them.
+     * Thanks to the brain-dead persistent naming schemes on udev-
+     * based Linux systems those actually are quite common.
+     */
+    drv1 = find_hdev_driver(filename);
+    if (drv1) {
+        return drv1;
+    }
+
 #ifdef _WIN32
-    is_drive = is_windows_drive(filename) ||
-        is_windows_drive_prefix(filename);
-#else
-    is_drive = 0;
+     if (is_windows_drive(filename) ||
+         is_windows_drive_prefix(filename))
+         return bdrv_find_format("file");
 #endif
+
     p = strchr(filename, ':');
-    if (!p || is_drive) {
-        drv1 = find_hdev_driver(filename);
-        if (!drv1) {
-            drv1 = bdrv_find_format("file");
-        }
-        return drv1;
+    if (!p) {
+        return bdrv_find_format("file");
     }
     len = p - filename;
     if (len > sizeof(protocol) - 1)