Re: [Qemu-devel] [Qemu-stable] [PATCH] block/vpc: fix get_sector_offset for vpc_read

[Peter Lieven <pl@kamp.de>]

Am 23.02.2015 um 18:10 schrieb Max Reitz:
> On 2015-02-23 at 10:01, Peter Lieven wrote:
>> VHD images contain a bitmap at the beginning of each data block
>> to indicate the allocation status of each sector in the data block.
>>
>> vpc_read currently checks the allocation status of the first sector
>> in a data block it is going to read and then assumes the same allocation
>> status for the whole remainder of the data block. This might end up
>> in incorrect zero sectors if the first sector is unallocated.
>>
>> To fix this indiciate a sector is allocated as soon as its
>> data block has a valid page table index.
>
> Hm, as far as I can see, this patch just removes unused code. How does this correspond to the commit message?

Oh, you are right. I was somehow believing that the #if 0 was just disabling the cache.

Please ignore this one.

Peter

>
> Max
>
>> CC: qemu-stable@nongnu.org
>> Signed-off-by: Peter Lieven <pl@kamp.de>
>> ---
>>   block/vpc.c |   32 --------------------------------
>>   1 file changed, 32 deletions(-)
>>
>> diff --git a/block/vpc.c b/block/vpc.c
>> index 46803b1..9a75334 100644
>> --- a/block/vpc.c
>> +++ b/block/vpc.c
>> @@ -376,38 +376,6 @@ static inline int64_t get_sector_offset(BlockDriverState *bs,
>>           bdrv_pwrite_sync(bs->file, bitmap_offset, bitmap, s->bitmap_size);
>>       }
>>   -//    printf("sector: %" PRIx64 ", index: %x, offset: %x, bioff: %" PRIx64 ", bloff: %" PRIx64 "\n",
>> -//    sector_num, pagetable_index, pageentry_index,
>> -//    bitmap_offset, block_offset);
>> -
>> -// disabled by reason
>> -#if 0
>> -#ifdef CACHE
>> -    if (bitmap_offset != s->last_bitmap)
>> -    {
>> -    lseek(s->fd, bitmap_offset, SEEK_SET);
>> -
>> -    s->last_bitmap = bitmap_offset;
>> -
>> -    // Scary! Bitmap is stored as big endian 32bit entries,
>> -    // while we used to look it up byte by byte
>> -    read(s->fd, s->pageentry_u8, 512);
>> -    for (i = 0; i < 128; i++)
>> -        be32_to_cpus(&s->pageentry_u32[i]);
>> -    }
>> -
>> -    if ((s->pageentry_u8[pageentry_index / 8] >> (pageentry_index % 8)) & 1)
>> -    return -1;
>> -#else
>> -    lseek(s->fd, bitmap_offset + (pageentry_index / 8), SEEK_SET);
>> -
>> -    read(s->fd, &bitmap_entry, 1);
>> -
>> -    if ((bitmap_entry >> (pageentry_index % 8)) & 1)
>> -    return -1; // not allocated
>> -#endif
>> -#endif
>> -
>>       return block_offset;
>>   }
>
>


-- 

Mit freundlichen Grüßen

Peter Lieven

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