Re: [Qemu-devel] [PATCH 1/4] block/parallels: extend parallels format header with actual data values

[Jeff Cody]

On Tue, Jul 22, 2014 at 05:19:34PM +0400, Denis V. Lunev wrote:
> Parallels image format has several additional fields inside:
> - nb_sectors is actually 64 bit wide. Upper 32bits are not used for
>   images with signature "WithoutFreeSpace" and must be explicitely

s/explicitely/explicitly

>   zeroed according to Parallels. They will be used for images with
>   signature "WithouFreSpacExt"
> - inuse is magic which means that the image is currently opened for
>   read/write or was not closed correctly, the magic is 0x746f6e59
> - data_off is the location of the first data block. It can be zero
>   and in this case

I think you may have forgotten to finish this sentence :)

> 
> This patch adds these values to struct parallels_header and adds
> proper handling of nb_sectors for currently supported WithoutFreeSpace
> images.
> 
> WithouFreSpacExt will be covered in the next patch.
> 
> Signed-off-by: Denis V. Lunev <address@hidden>
> CC: Kevin Wolf <address@hidden>
> CC: Stefan Hajnoczi <address@hidden>
> ---
>  block/parallels.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/block/parallels.c b/block/parallels.c
> index 1a5bd35..c44df87 100644
> --- a/block/parallels.c
> +++ b/block/parallels.c
> @@ -41,8 +41,10 @@ struct parallels_header {
>      uint32_t cylinders;
>      uint32_t tracks;
>      uint32_t catalog_entries;
> -    uint32_t nb_sectors;
> -    char padding[24];
> +    uint64_t nb_sectors;
> +    uint32_t inuse;
> +    uint32_t data_off;
> +    char padding[12];
>  } QEMU_PACKED;
>  
>  typedef struct BDRVParallelsState {
> @@ -90,7 +92,7 @@ static int parallels_open(BlockDriverState *bs, QDict 
> *options, int flags,
>          goto fail;
>      }
>  
> -    bs->total_sectors = le32_to_cpu(ph.nb_sectors);
> +    bs->total_sectors = (uint32_t)le64_to_cpu(ph.nb_sectors);

I think an explicit bit mask on the upper 32 bits would fit better
here than a cast, especially since neither 'bs->total_sectors' nor
'ph.nb_sectors' is a uint32_t. E.g.:

    bs->total_sectors = 0xffffffff & le64_to_cpu(ph.nb_sectors);


>  
>      s->tracks = le32_to_cpu(ph.tracks);
>      if (s->tracks == 0) {
> -- 
> 1.9.1
> 
>