Re: [PATCH] vhost-user-input: use free(elem) instead of g_free(elem)

["Daniel P. Berrangé" <berrange@redhat.com>]

On Tue, Nov 19, 2019 at 11:16:26AM +0000, Stefan Hajnoczi wrote:
> The virtqueue element returned by vu_queue_pop() is allocated using
> malloc(3) by virtqueue_alloc_element().  Use the matching free(3)
> function instead of glib's g_free().

Just as an FYI, since glib 2.46  g_malloc is hardcoded to use the
system allocator, so it is now guaranteed that g_malloc/malloc
and g_free/free are safely interchangable. I recently got this
clarified in the glib docs:

  https://gitlab.gnome.org/GNOME/glib/merge_requests/1099//diffs

QEMU mandates 2.48 so we are now safe in that regard

For readability/sanity sake I'd still suggest matching functions
but it is not a functional danger any more. Even when it was a
risk, that risk only arose if you called GLib's API for installing
a custom allocator callback which QEMU never did, so it was always
a non-issue.

Where this is most helpful is in exchanging allocated data with
3rd party libraries that don't use glib. We no longer have to
worry about dup'ing memory going in/out libraries not using
glib's allocators.

> 
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  contrib/vhost-user-input/main.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/contrib/vhost-user-input/main.c b/contrib/vhost-user-input/main.c
> index 449fd2171a..ef4b7769f2 100644
> --- a/contrib/vhost-user-input/main.c
> +++ b/contrib/vhost-user-input/main.c
> @@ -77,7 +77,7 @@ static void vi_input_send(VuInput *vi, struct virtio_input_event *event)
>          len = iov_from_buf(elem->in_sg, elem->in_num,
>                             0, &vi->queue[i].event, sizeof(virtio_input_event));
>          vu_queue_push(dev, vq, elem, len);
> -        g_free(elem);
> +        free(elem);
>      }
>  
>      vu_queue_notify(&vi->dev.parent, vq);
> @@ -153,7 +153,7 @@ static void vi_handle_sts(VuDev *dev, int qidx)
>                           0, &event, sizeof(event));
>          vi_handle_status(vi, &event);
>          vu_queue_push(dev, vq, elem, len);
> -        g_free(elem);
> +        free(elem);
>      }
>  
>      vu_queue_notify(&vi->dev.parent, vq);
> -- 
> 2.23.0
> 
> 

Regards,
Daniel
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