[Qemu-devel] [PATCH 6/6] vvfat: reorganize computation of disk geometry

[Paolo Bonzini <pbonzini@redhat.com>]

First determine FAT12/16/32, then compute geometry from that for both
FDD and HDD.  For floppies, change to 1 sector/cluster since the limit
for that is ~2 MB for FAT12 (which we use for 1.44 MB floppies only)
and well over 2.88 MB for FAT16.

This matches the actual format used by 1.44 MB floppies.  Real 2.88 MB
floppies used FAT12 with 2 sectors/cluster.  This patch does not make
things worse than they were before it, though.

FAT32 is totally broken.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 block/vvfat.c |   30 +++++++++++++++---------------
 1 files changed, 15 insertions(+), 15 deletions(-)

diff --git a/block/vvfat.c b/block/vvfat.c
index fb3d62e..1a0216c 100644
--- a/block/vvfat.c
+++ b/block/vvfat.c
@@ -996,7 +996,6 @@ static int is_consistent(BDRVVVFATState *s);
 static int vvfat_open(BlockDriverState *bs, const char* dirname, int flags)
 {
     BDRVVVFATState *s = bs->opaque;
-    int floppy = 0;
     int i;
 
 #ifdef DEBUG
@@ -1013,8 +1012,6 @@ DLOG(if (stderr == NULL) {
     s->fat_type=16;
     /* LATER TODO: if FAT32, adjust */
     s->sectors_per_cluster=0x10;
-    /* 504MB disk*/
-    bs->cyls=1024; bs->heads=16; bs->secs=63;
 
     s->current_cluster=0xffffffff;
 
@@ -1029,14 +1026,6 @@ DLOG(if (stderr == NULL) {
     if (!strstart(dirname, "fat:", NULL))
 	return -1;
 
-    if (strstr(dirname, ":floppy:")) {
-	floppy = 1;
-	s->fat_type = 12;
-	s->first_sectors_number = 1;
-	s->sectors_per_cluster=2;
-	bs->cyls = 80; bs->heads = 2; bs->secs = 36;
-    }
-
     if (strstr(dirname, ":32:")) {
 	fprintf(stderr, "Big fat greek warning: FAT32 has not been tested. You are welcome to do so!\n");
 	s->fat_type = 32;
@@ -1044,7 +1033,18 @@ DLOG(if (stderr == NULL) {
 	s->fat_type = 16;
     } else if (strstr(dirname, ":12:")) {
 	s->fat_type = 12;
-	bs->secs = 18;
+    }
+
+    if (strstr(dirname, ":floppy:")) {
+	/* Real ED floppies used FAT12, 2 sec/cluster.  Take a shortcut.  */
+	s->first_sectors_number = 1;
+	s->sectors_per_cluster=1;
+	bs->cyls=80; bs->heads=2;
+	bs->secs=(s->fat_type == 12 ? 18 : 36);
+    } else {
+	/* 32MB or 504MB disk*/
+	bs->cyls=(s->fat_type == 12 ? 64 : 1024);
+	bs->heads=16; bs->secs=63;
     }
 
     s->sector_count=bs->cyls*bs->heads*bs->secs-(s->first_sectors_number-1);
@@ -1072,10 +1072,10 @@ DLOG(if (stderr == NULL) {
 
     if(s->first_sectors_number==0x40)
 	init_mbr(s);
-
-    /* for some reason or other, MS-DOS does not like to know about CHS... */
-    if (floppy)
+    else {
+        /* MS-DOS does not like to know about CHS (?). */
 	bs->heads = bs->cyls = bs->secs = 0;
+    }
 
     //    assert(is_consistent(s));
     return 0;
-- 
1.7.6