Re: [Qemu-devel] [PATCH for-2.3 3/6] vmdk: Clean up descriptor file reading

[Don Koch]

On Tue, 2 Dec 2014 15:39:14 +0800
Fam Zheng <address@hidden> wrote:

> Zeroing a buffer that will be filled right after is not necessary, and
> allocating a power of two + 1 is naughty.
> 
> Suggested-by: Markus Armbruster <address@hidden>
> Signed-off-by: Fam Zheng <address@hidden>
> ---
>  block/vmdk.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/block/vmdk.c b/block/vmdk.c
> index 28d22db..0c5769c 100644
> --- a/block/vmdk.c
> +++ b/block/vmdk.c
> @@ -558,14 +558,15 @@ static char *vmdk_read_desc(BlockDriverState *file, 
> uint64_t desc_offset,
>      }
>  
>      size = MIN(size, 1 << 20);  /* avoid unbounded allocation */
> -    buf = g_malloc0(size + 1);
> +    buf = g_malloc(size);

For a file that is less than 1<<20 bytes, won't this throw away the last byte?
Maybe better is:
    size = MIN(size, (1 << 20) - 1);
    buf = g_malloc(size + 1);
Leave the bdrv_pread as it was and...

>  
> -    ret = bdrv_pread(file, desc_offset, buf, size);
> +    ret = bdrv_pread(file, desc_offset, buf, size - 1);
>      if (ret < 0) {
>          error_setg_errno(errp, -ret, "Could not read from file");
>          g_free(buf);
>          return NULL;
>      }
> +    buf[ret - 1] = 0;

...zero the last byte changes to:
    buf[ret] = 0;

>  
>      return buf;
>  }
> -- 
> 1.9.3

-d