Re: [PATCH v4 1/7] nbd: Utilize QAPI_CLONE for type conversion

[Eric Blake <eblake@redhat.com>]

On 10/9/20 4:55 PM, Eric Blake wrote:
> Rather than open-coding the translation from the deprecated
> NbdServerAddOptions type to the preferred BlockExportOptionsNbd, it's
> better to utilize QAPI_CLONE_MEMBERS.  This solves a couple of issues:
> first, if we do any more refactoring of the base type (which an
> upcoming patch plans to do), we don't have to revisit the open-coding.
> Second, our assignment to arg->name is fishy: the generated QAPI code
> currently does not visit it if arg->has_name is false, but if it DID
> visit it, we would have introduced a double-free situation when arg is
> finally freed.
> 
> Signed-off-by: Eric Blake <eblake@redhat.com>
> ---
>  blockdev-nbd.c | 15 ++++++---------
>  1 file changed, 6 insertions(+), 9 deletions(-)

v5 will fix this nasty bug:


> @@ -195,7 +197,8 @@ void qmp_nbd_server_add(NbdServerAddOptions *arg, Error **errp)
>       * the device name as a default here for compatibility.
>       */
>      if (!arg->has_name) {
> -        arg->name = arg->device;
> +        arg->has_name = true;
> +        arg->name = g_steal_pointer(&arg->device);
>      }

This causes assertion failures visible in at least iotest 149 and 192,
because arg->device was left NULL.  Using g_strdup() instead fixes that.

> 
>      export_opts = g_new(BlockExportOptions, 1);
> @@ -205,15 +208,9 @@ void qmp_nbd_server_add(NbdServerAddOptions *arg, Error **errp)
>          .node_name              = g_strdup(bdrv_get_node_name(bs)),
>          .has_writable           = arg->has_writable,
>          .writable               = arg->writable,
> -        .u.nbd = {
> -            .has_name           = true,
> -            .name               = g_strdup(arg->name),
> -            .has_description    = arg->has_description,
> -            .description        = g_strdup(arg->description),
> -            .has_bitmap         = arg->has_bitmap,
> -            .bitmap             = g_strdup(arg->bitmap),
> -        },
>      };
> +    QAPI_CLONE_MEMBERS(BlockExportOptionsNbd, &export_opts->u.nbd,
> +                       qapi_NbdServerAddOptions_base(arg));
> 
>      /*
>       * nbd-server-add doesn't complain when a read-only device should be
> 

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