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Re: [Qemu-devel] [PATCH 03/32] vvfat: Fix partition table
From: |
Kevin Wolf |
Subject: |
Re: [Qemu-devel] [PATCH 03/32] vvfat: Fix partition table |
Date: |
Wed, 04 Jul 2012 17:17:27 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:13.0) Gecko/20120605 Thunderbird/13.0 |
Am 29.06.2012 22:33, schrieb 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.
For compensation there's an extra space before the '='.
>> + partition->length_sector_long = cpu_to_le32(s->bs->total_sectors
>> + - s->first_sectors_number +
>> 1);
Just wondering... This should be the same as s->sector_count, right?
This whole geometry calculation code in vvfat is way too convoluted to
understand when you haven't looked at it for some months...
Kevin
- Re: [Qemu-devel] [PATCH 03/32] vvfat: Fix partition table,
Kevin Wolf <=