Re: [PATCH v3 2/5] vvfat: move fat_type check prior to size setup

[BALATON Zoltan]

On Thu, 27 Nov 2025, Clément Chigot wrote:
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.
The selection of floppy size was a bit unusual:
- fat-type undefined: a FAT 12 2880 Kib disk (default)
- fat-type=16: a FAT 16 2880 Kib disk
- fat-type=12: a FAT 12 1440 Kib disk

Now, that fat-type undefined means fat-type=12, it's no longer possible
to make that size distinction. Therefore, it's being changed for the
following:
- fat-type=12: a FAT 12 1440 Kib disk (default)
- fat-type=16: a FAT 16 2880 Kib dis

This has been choosen for two reasons: keep fat-type=12 the default and
create a more usual size for it: 1440 Kib.

The possibility to create a FAT 12 2880 KiB floppy will be added back
later, through the fs-size parameter.

Signed-off-by: Clément Chigot <chi...@adacore.com>
---
block/vvfat.c | 43 ++++++++++++++++++++++---------------------
1 file changed, 22 insertions(+), 21 deletions(-)

diff --git a/block/vvfat.c b/block/vvfat.c
index dd0b3689c1..baf04e678b 100644
--- a/block/vvfat.c
+++ b/block/vvfat.c
@@ -1188,28 +1188,8 @@ 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) {
-            s->fat_type = 12;
-            secs = 36;
-            s->sectors_per_cluster = 2;
-        } else {
-            secs = s->fat_type == 12 ? 18 : 36;
-            s->sectors_per_cluster = 1;
-        }
-        cyls = 80;
-        heads = 2;
-    } else {
-        /* 32MB or 504MB disk*/
-        if (!s->fat_type) {
-            s->fat_type = 16;
-        }
-        cyls = s->fat_type == 12 ? 64 : 1024;
-        heads = 16;
-        secs = 63;
-    }

+    /* Verify FAT type  */
    switch (s->fat_type) {
    case 32:
        warn_report("FAT32 has not been tested. You are welcome to do so!");
@@ -1217,12 +1197,33 @@ static int vvfat_open(BlockDriverState *bs, QDict 
*options, int flags,
    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) {
+        /* Choose floppy size. 1440 KiB for FAT 12, 2880 KiB for FAT-16 */
+        secs = s->fat_type == 12 ? 18 : 36;
+        cyls = 80;
+        heads = 2;
+    } else {
+        /* 32MB or 504MB disk*/
+        cyls = s->fat_type == 12 ? 64 : 1024;
+        heads = 16;
+        secs = 63;
+    }
+
    /* Reserver space for MBR */

Previous patch but only noticed here. This may be correct in French but in 
English to many r-s in Reserve.

Regards,
BALATON Zoltan

    if (partitioned) {
        s->offset_to_bootsector = 0x3f;