On Wed, Oct 29, 2014 at 04:38:09PM +0300, Denis V. Lunev wrote:
> Unfortunately, old guest OSes do not align partitions to page size by
> default. This is true for Windows 2003 and Windows XP.
>
> For the time being Parallels was created an optimization for such OSes
> in its desktop product. Desktop users are not qualified enough to create
> properly aligned installations. Thus Parallels makes a blind guess
> on a customer behalf and creates so-called "padded" images if guest
> OS type is specified as WinXP, Win2k and Win2k3.
>
> "Padding" is a value which should be added to guest LBA to obtain
> sector number inside the image. This results in a shifted images.
> 0123 offset inside image (in 512 byte sectors)
> +-------
> +.012 guest data (512 byte sectors)
> +-------
> The information about this is available in DiskDescriptor.xml ONLY. There
> is no such data in the image header.
>
> There share of such images could be evaluated as 6-8% according to the
> statistics in my hands.
>
> This patch obtains proper value from XML and applies it on reading.
>
> Signed-off-by: Denis V. Lunev <d...@openvz.org>
> Acked-by: Roman Kagan <rka...@parallels.com>
> CC: Jeff Cody <jc...@redhat.com>
> CC: Kevin Wolf <kw...@redhat.com>
> CC: Stefan Hajnoczi <stefa...@redhat.com>
> ---
> block/parallels.c | 19 +++++++++++++++++++
> 1 file changed, 19 insertions(+)
>
> diff --git a/block/parallels.c b/block/parallels.c
> index 201c0f1..d07e4f7 100644
> --- a/block/parallels.c
> +++ b/block/parallels.c
> @@ -66,6 +66,7 @@ typedef struct BDRVParallelsState {
> unsigned int tracks;
>
> unsigned int off_multiplier;
> + unsigned int padding;
> } BDRVParallelsState;
>
> static int parallels_open_image(BlockDriverState *bs, Error **errp);
> @@ -144,6 +145,7 @@ static int parallels_open_xml(BlockDriverState *bs, int
> flags, Error **errp)
> const char *data;
> char image_path[PATH_MAX];
> Error *local_err = NULL;
> + BDRVParallelsState *s = bs->opaque;
>
> ret = size = bdrv_getlength(bs->file);
> if (ret < 0) {
> @@ -173,6 +175,19 @@ static int parallels_open_xml(BlockDriverState *bs, int
> flags, Error **errp)
> if (root == NULL) {
> goto fail;
> }
> +
> + data = xml_get_text(root, "/Disk_Parameters/Padding");
> + if (data != NULL) {
> + char *endptr;
> + unsigned long pad;
> +
> + pad = strtoul(data, &endptr, 0);
> + if ((endptr != NULL && *endptr != '\0') || pad > UINT_MAX) {
> + goto fail;
> + }
> + s->padding = (uint32_t)pad;
> + }
> +
> image = xml_seek(root, "/StorageData/Storage/Image");
> data = ""; /* make gcc happy */
> for (size = 0; image != NULL; image = image->next) {
> @@ -385,6 +400,10 @@ static int64_t seek_to_sector(BlockDriverState *bs,
> int64_t sector_num)
> static int parallels_read(BlockDriverState *bs, int64_t sector_num,
> uint8_t *buf, int nb_sectors)
> {
> + BDRVParallelsState *s = bs->opaque;
> +
> + sector_num += s->padding;
> +
> while (nb_sectors > 0) {
> int64_t position = seek_to_sector(bs, sector_num);
> if (position >= 0) {
> --
> 1.9.1
>
Reviewed-by: Jeff Cody <jc...@redhat.com>
