This allows to handle the default FAT size in a single place and make the
following part taking care only about size parameters. It will be later
moved away in a specific function.

Setting a floppy disk of 1MB is no longer possible as it was a side
effect of passing "fat-type=12". To be precise there were three cases:
 - fat-type undefined (aka default): a fat12 2MB disk
 - fat-type=16: a fat16 2Mb disk
 - fat-type=12: a fat12 1Mb disk

Now, that fat-type undefined means fat-type=2, it's no longer possible
to make that size distinction. It will be added back a bit later,
through the size parameter.

Signed-off-by: Clément Chigot <chigot@adacore.com>
---
 block/vvfat.c | 48 +++++++++++++++++++++++++++---------------------
 1 file changed, 27 insertions(+), 21 deletions(-)

diff --git a/block/vvfat.c b/block/vvfat.c
index 0220dd828b..91e4ad3158 100644
--- a/block/vvfat.c
+++ b/block/vvfat.c
@@ -1190,45 +1190,51 @@ static int vvfat_open(BlockDriverState *bs, QDict *options, int flags,
         memcpy(s->volume_label, "QEMU VVFAT", 10);
     }
 
-    if (floppy) {
-        /* 1.44MB or 2.88MB floppy.  2.88MB can be FAT12 (default) or FAT16. */
-        if (!s->fat_type) {
+    /* Verify FAT type  */
+    switch (s->fat_type) {
+    case 32:
+        warn_report("FAT32 has not been tested. You are welcome to do so!");
+        break;
+    case 16:
+    case 12:
+        break;
+    case 0:
+        /* Set a default type */
+        if (floppy) {
             s->fat_type = 12;
+        } else {
+            s->fat_type = 16;
+        }
+        break;
+    default:
+        error_setg(errp, "Valid FAT types are only 12, 16 and 32");
+        ret = -EINVAL;
+        goto fail;
+    }
+
+
+    if (floppy) {
+        /* 2.88MB floppy */
+        if (s->fat_type == 12) {
             secs = 36;
             s->sectors_per_cluster = 2;
         } else {
-            secs = s->fat_type == 12 ? 18 : 36;
+            secs = 36;
             s->sectors_per_cluster = 1;
         }
         cyls = 80;
         heads = 2;
     } else {
-        /* 32MB or 504MB disk*/
-        if (!s->fat_type) {
-            s->fat_type = 16;
-        }
         /* Reserver space for MBR */
         if (!qemu_opt_get_bool(opts, "no-mbr", false)) {
             s->offset_to_bootsector = 0x3f;
         }
+        /* 32MB or 504MB disk*/
         cyls = s->fat_type == 12 ? 64 : 1024;
         heads = 16;
         secs = 63;
     }
 
-    switch (s->fat_type) {
-    case 32:
-        warn_report("FAT32 has not been tested. You are welcome to do so!");
-        break;
-    case 16:
-    case 12:
-        break;
-    default:
-        error_setg(errp, "Valid FAT types are only 12, 16 and 32");
-        ret = -EINVAL;
-        goto fail;
-    }
-
 
     s->bs = bs;
 
-- 
2.34.1