Re: [Qemu-devel] [RFC PATCH 11/14] allow writing to the backing file

[Max Reitz]

On 2015-02-11 at 22:07, Wen Congyang wrote:
> Signed-off-by: Wen Congyang <address@hidden>
> Signed-off-by: zhanghailiang <address@hidden>
> Signed-off-by: Gonglei <address@hidden>
> ---
>   block.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)

I don't think this is a good idea. With this patch, every time you open 
a COW file (with a backing file) R/W, the backing file will be writable. 
I'd rather like a way to explicitly overwrite the R/W mode of the 
backing file; but by default, in my opinion, it should stay read-only.

Max

> diff --git a/block.c b/block.c
> index 067c44b..96cf973 100644
> --- a/block.c
> +++ b/block.c
> @@ -856,8 +856,8 @@ static int bdrv_inherited_flags(int flags)
>    */
>   static int bdrv_backing_flags(int flags)
>   {
> -    /* backing files always opened read-only */
> -    flags &= ~(BDRV_O_RDWR | BDRV_O_COPY_ON_READ);
> +    /* backing files are opened read-write for block replication */
> +    flags &= ~BDRV_O_COPY_ON_READ;
>   
>       /* snapshot=on is handled on the top layer */
>       flags &= ~(BDRV_O_SNAPSHOT | BDRV_O_TEMPORARY);