Re: [Xen-devel] [PATCH] blktap2: Invalid logic detecting unaligned buffers in vhd_write_block

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Thu, Mar 17, 2016 at 06:10:59PM -0400, Ross Philipson wrote:
> It seems the logic is meant to detect sector unaligned buffers for block
> writes. The NOTing of the logic instead masks off any unaligned bits and
> also would cause the function to always fail. It seems the function is not
> used in any of the tools so that is probably why the problem is not seen.
> In the vhd_read_block function it is correct.
> 
> Signed-off-by: Ross Philipson <ross.philipson@xxxxxxxxxxxx>

This seems to fall under tools umbrella. I've look at blktap2 code,
the reasoning is convincing to me so:

  Acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>

But I've never used blktap2 and we don't normally test it so I would
also wait a bit longer to see if anybody objects to this change.

OOI if no code was using this, how did you discover this problem?

Wei.

> ---
> diff --git a/tools/blktap2/vhd/lib/libvhd.c b/tools/blktap2/vhd/lib/libvhd.c
> index 1fd5b4e..4ebe012 100644
> --- a/tools/blktap2/vhd/lib/libvhd.c
> +++ b/tools/blktap2/vhd/lib/libvhd.c
> @@ -2188,7 +2188,7 @@ vhd_write_block(vhd_context_t *ctx, uint32_t block, 
> char *data)
>         if (block >= ctx->bat.entries)
>                 return -ERANGE;
> 
> -       if ((unsigned long)data & ~(VHD_SECTOR_SIZE -1))
> +       if ((unsigned long)data & (VHD_SECTOR_SIZE -1))
>                 return -EINVAL;
> 
>         blk  = ctx->bat.bat[block];
> 
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