Re: [Qemu-devel] [PATCH 03/32] vvfat: Fix partition table

[Blue Swirl]

On Fri, Jun 29, 2012 at 3:34 PM, Markus Armbruster <address@hidden> wrote:
> Unless parameter ":floppy:" is given, vvfat creates a virtual image
> with DOS MBR defining a single partition which holds the FAT file
> system.  The size of the virtual image depends on the width of the
> FAT: 32 MiB (CHS 64, 16, 63) for 12 bit FAT, 504 MiB (CHS 1024, 16,
> 63) for 16 and 32 bit FAT, leaving (64*16-1)*63 = 64449 and
> (1024*16-1)*64 = 1032129 sectors for the partition.
>
> However, it screws up the end of the partition in the MBR:
>
>    FAT width param.  start CHS  end CHS     start LBA  size
>        :32:          0,1,1      1023,14,63       63    1032065
>        :16:          0,1,1      1023,14,55       63    1032057
>        :12:          0,1,1        63,14,55       63      64377
>
> The actual FAT file system nevertheless assumes the partition has
> 1032129 or 64449 sectors.  Oops.
>
> Signed-off-by: Markus Armbruster <address@hidden>
> ---
>  block/vvfat.c |    7 ++++---
>  1 files changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/block/vvfat.c b/block/vvfat.c
> index 0fd3367..62745b5 100644
> --- a/block/vvfat.c
> +++ b/block/vvfat.c
> @@ -394,11 +394,12 @@ static void init_mbr(BDRVVVFATState* s)
>
>     /* LBA is used when partition is outside the CHS geometry */
>     lba = sector2CHS(s->bs, &partition->start_CHS, s->first_sectors_number-1);
> -    lba|= sector2CHS(s->bs, &partition->end_CHS,   s->sector_count);
> +    lba |= sector2CHS(s->bs, &partition->end_CHS, s->bs->total_sectors - 1);
>
>     /*LBA partitions are identified only by start/length_sector_long not by 
> CHS*/
> -    partition->start_sector_long =cpu_to_le32(s->first_sectors_number-1);
> -    partition->length_sector_long=cpu_to_le32(s->sector_count - 
> s->first_sectors_number+1);
> +    partition->start_sector_long  = cpu_to_le32(s->first_sectors_number-1);

Spaces around '-'. Thanks for fixing the other cases, BTW.

> +    partition->length_sector_long = cpu_to_le32(s->bs->total_sectors
> +                                                - s->first_sectors_number + 
> 1);
>
>     /* FAT12/FAT16/FAT32 */
>     /* DOS uses different types when partition is LBA,
> --
> 1.7.6.5
>
>