Re: [Qemu-devel] [PATCH 1/1] block/vpc.c: Detect too-large vpc file

[Kevin Wolf <kwolf@redhat.com>]

Am 25.07.2011 20:34, schrieb Serge E. Hallyn:
> VHD files technically can be up to 2Tb, but virtual pc is limited
> to 127G.  Currently qemu-img refused to create vpc files > 127G,
> but it is failing to return error when converting from a non-vpc
> VHD file which is >127G.  It returns success, but creates a truncated
> converted image.  Also, qemu-img info claims the vpc file is 127G
> (and clean).
> 
> This patch detects a too-large vpc file and returns -EFBIG.  Without
> this patch,
> 
> =============================================================
> root@ip-10-38-123-242:~/qemu-fixed# qemu-img info /mnt/140g-dynamic.vhd 
> image: /mnt/140g-dynamic.vhd
> file format: vpc
> virtual size: 127G (136899993600 bytes)
> disk size: 284K
> root@ip-10-38-123-242:~/qemu-fixed# qemu-img convert -f vpc -O raw /mnt/140g-dynamic.vhd /mnt/y
> root@ip-10-38-123-242:~/qemu-fixed# echo $?
> 0
> root@ip-10-38-123-242:~/qemu-fixed# qemu-img info /mnt/y
> image: /mnt/y
> file format: raw
> virtual size: 127G (136899993600 bytes)
> disk size: 0
> =============================================================
> 
> (The 140G image was truncated with no warning or error.)
> 
> With the patch, I get:
> 
> =============================================================
> root@ip-10-38-123-242:~/qemu-fixed# ./qemu-img info /mnt/140g-dynamic.vhd 
> qemu-img: Could not open '/mnt/140g-dynamic.vhd': File too large
> root@ip-10-38-123-242:~/qemu-fixed# ./qemu-img convert -f vpc -O raw /mnt/140g-dynamic.vhd /mnt/y
> qemu-img: Could not open '/mnt/140g-dynamic.vhd': File too large
> qemu-img: Could not open '/mnt/140g-dynamic.vhd'
> =============================================================
> 
> See https://bugs.launchpad.net/qemu/+bug/814222 for details.
> 
> Signed-off-by: Serge Hallyn <serge.hallyn@canonical.com>
> ---
>  block/vpc.c |    8 +++++++-
>  1 files changed, 7 insertions(+), 1 deletions(-)
> 
> diff --git a/block/vpc.c b/block/vpc.c
> index 56865da..fdd5236 100644
> --- a/block/vpc.c
> +++ b/block/vpc.c
> @@ -156,6 +156,7 @@ static int vpc_open(BlockDriverState *bs, int flags)
>      struct vhd_dyndisk_header* dyndisk_header;
>      uint8_t buf[HEADER_SIZE];
>      uint32_t checksum;
> +    int err = -1;
>  
>      if (bdrv_pread(bs->file, 0, s->footer_buf, HEADER_SIZE) != HEADER_SIZE)
>          goto fail;
> @@ -176,6 +177,11 @@ static int vpc_open(BlockDriverState *bs, int flags)
>      bs->total_sectors = (int64_t)
>          be16_to_cpu(footer->cyls) * footer->heads * footer->secs_per_cyl;
>  
> +    if (bs->total_sectors >= 65535 * 16 * 255) {
> +        err = -EFBIG;
> +        goto fail;
> +    }

I wonder why this works. If bs->total_sectors was right, shouldn't it
have converted the full 140 GB? I can't see where else we would limit it
to 127 GB, so what I had expected is that the CHS geometry stored in the
image header is already too small.

What is the CHS geometry of this 140 GB image?

Kevin