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Re: [Qemu-devel] [PATCH 2/2] vmdk: Read footer for streamOptimized image
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH 2/2] vmdk: Read footer for streamOptimized images |
Date: |
Thu, 16 Aug 2012 10:17:06 +0100 |
On Thu, Aug 16, 2012 at 9:54 AM, Kevin Wolf <address@hidden> wrote:
> The footer takes precedence over the header when it exists. It contains
> the real grain directory offset that is missing in the header. Without
> this patch, streamOptimized images with a footer cannot be read.
>
> Signed-off-by: Kevin Wolf <address@hidden>
> ---
> block/vmdk.c | 16 ++++++++++++++++
> 1 files changed, 16 insertions(+), 0 deletions(-)
>
> diff --git a/block/vmdk.c b/block/vmdk.c
> index 9648398..c243a96 100644
> --- a/block/vmdk.c
> +++ b/block/vmdk.c
> @@ -35,6 +35,7 @@
> #define VMDK4_FLAG_RGD (1 << 1)
> #define VMDK4_FLAG_COMPRESS (1 << 16)
> #define VMDK4_FLAG_MARKER (1 << 17)
> +#define VMDK4_GD_AT_END 0xffffffffffffffffULL
>
> typedef struct {
> uint32_t version;
> @@ -451,6 +452,21 @@ static int vmdk_open_vmdk4(BlockDriverState *bs,
> if (header.capacity == 0 && header.desc_offset) {
> return vmdk_open_desc_file(bs, flags, header.desc_offset << 9);
> }
> +
> + if (header.gd_offset == VMDK4_GD_AT_END) {
> + /*
> + * The footer takes precedence over the header, so read it in. The
> + * footer starts at offset -1024 from the end: One sector for the
> + * footer, and another one for the end-of-stream marker.
> + */
> + ret = bdrv_pread(file,
> + bs->file->total_sectors * 512 - 1024 + sizeof(magic),
> + &header, sizeof(header));
> + if (ret < 0) {
> + return ret;
> + }
> + }
> +
> l1_entry_sectors = le32_to_cpu(header.num_gtes_per_gte)
> * le64_to_cpu(header.granularity);
> if (l1_entry_sectors == 0) {
I think we should check the magic number or marker before trusting the
contents of the footer.
Stefan