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

[Peter Lieven]

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: address@hidden
> > Signed-off-by: Peter Lieven <address@hidden>
> > ---
> >   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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