raw-posix: Detect legacy floppy via ioctl on linux

Current legacy floppy detection is hardcoded based on source file
name. Make this smarter on linux by attempting a floppy specific
ioctl.

v2:
    Give ioctl check higher priority than filename check
    s/IDE/legacy/

v3:
    Actually initialize 'prio' variable
    Check for ioctl success rather than absence of specific failure

v4:
    Explicitly mention that change is linux specific.

Signed-off-by: Cole Robinson <crobinso@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

block/raw-posix.c

@@ -1055,9 +1055,26 @@ static int floppy_open(BlockDriverState *bs, const char *filename, int flags)
 
 static int floppy_probe_device(const char *filename)
 {
+    int fd, ret;
+    int prio = 0;
+    struct floppy_struct fdparam;
+
     if (strstart(filename, "/dev/fd", NULL))
-        return 100;
+        prio = 50;
-    return 0;
+
+    fd = open(filename, O_RDONLY | O_NONBLOCK);
+    if (fd < 0) {
+        goto out;
+    }
+
+    /* Attempt to detect via a floppy specific ioctl */
+    ret = ioctl(fd, FDGETPRM, &fdparam);
+    if (ret >= 0)
+        prio = 100;
+
+    close(fd);
+out:
+    return prio;
 }