Kevin Wolf <kw...@redhat.com> writes:
> Am 29.06.2012 22:33, schrieb Blue Swirl:
>> On Fri, Jun 29, 2012 at 3:34 PM, Markus Armbruster <arm...@redhat.com> 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 <arm...@redhat.com>
>>> ---
>>> 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 '='.
The original lined up the two '='. I preserved that. Not that I care
for it. Want me to drop the extra space?
>>> + 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?
Hmm. vvfat_open() assigns:
s->sector_count = cyls * heads * secs - (s->first_sectors_number - 1);
bs->total_sectors = cyls * heads * secs;
But it then changes it minds and does:
s->sector_count = s->faked_sectors +
s->sectors_per_cluster*s->cluster_count;
> This whole geometry calculation code in vvfat is way too convoluted to
> understand when you haven't looked at it for some months...
Yes, it is. I was briefly tempted to replace it, but then decided to
limit my footprint in this buck-crazy block driver to minimal bug fixes.
