Re: [PATCH V3 1/2] block/nbd: extract the common cleanup code

[Eric Blake <eblake@redhat.com>]

On 11/29/19 1:25 AM, pannengyuan@huawei.com wrote:
> From: PanNengyuan <pannengyuan@huawei.com>
> 
> The BDRVNBDState cleanup code is common in two places, add
> nbd_free_bdrvstate_prop() function to do these cleanups (suggested by
> Stefano Garzarella).
> 
> Signed-off-by: PanNengyuan <pannengyuan@huawei.com>
> ---
>   block/nbd.c | 23 +++++++++++++----------
>   1 file changed, 13 insertions(+), 10 deletions(-)
> 
> diff --git a/block/nbd.c b/block/nbd.c
> index 1239761..5805979 100644
> --- a/block/nbd.c
> +++ b/block/nbd.c
> @@ -94,6 +94,8 @@ typedef struct BDRVNBDState {
>   
>   static int nbd_client_connect(BlockDriverState *bs, Error **errp);
>   
> +static void nbd_free_bdrvstate_prop(BDRVNBDState *s);
> +

Why do you need a static function prototype?  Just implement the 
function prior to its first use, then you won't need a forward declaration.

>   static void nbd_channel_error(BDRVNBDState *s, int ret)
>   {
>       if (ret == -EIO) {
> @@ -1486,6 +1488,15 @@ static int nbd_client_connect(BlockDriverState *bs, Error **errp)
>       }
>   }
>   
> +static void nbd_free_bdrvstate_prop(BDRVNBDState *s)
> +{
> +    object_unref(OBJECT(s->tlscreds));
> +    qapi_free_SocketAddress(s->saddr);
> +    g_free(s->export);
> +    g_free(s->tlscredsid);
> +    g_free(s->x_dirty_bitmap);
> +}

In fact, it appears that you did just that, as the first use...

Bike-shedding: the name 'nbd_free_bdrvstate_prop' doesn't seem right to 
me - when I see a function with 'free' in the name taking a single 
pointer, I assume that the given pointer (here, BDRVNBDState *s) is 
freed - but your function does NOT free then incoming pointer.  Rather, 
you are clearing out the contents within a pre-allocated object which 
remains allocated.  What's more, since the object remains allocated, I'm 
surprised that you are not setting fields to NULL to prevent 
use-after-free bugs.

Either this function should also free s (in which case naming it merely 
'nbd_free_bdrvstate' might be better), or you should consider naming it 
'nbd_clear_bdrvstate' and assigning cleared fields to NULL.

> +
>   /*
>    * Parse nbd_open options
>    */
> @@ -1855,10 +1866,7 @@ static int nbd_process_options(BlockDriverState *bs, QDict *options,
>   
>    error:
>       if (ret < 0) {
> -        object_unref(OBJECT(s->tlscreds));
> -        qapi_free_SocketAddress(s->saddr);
> -        g_free(s->export);
> -        g_free(s->tlscredsid);
> +        nbd_free_bdrvstate_prop(s);

...is here.

>       }
>       qemu_opts_del(opts);
>       return ret;
> @@ -1937,12 +1945,7 @@ static void nbd_close(BlockDriverState *bs)
>       BDRVNBDState *s = bs->opaque;
>   
>       nbd_client_close(bs);
> -
> -    object_unref(OBJECT(s->tlscreds));
> -    qapi_free_SocketAddress(s->saddr);
> -    g_free(s->export);
> -    g_free(s->tlscredsid);
> -    g_free(s->x_dirty_bitmap);
> +    nbd_free_bdrvstate_prop(s);
>   }
>   
>   static int64_t nbd_getlength(BlockDriverState *bs)
> 

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org