Re: [PATCH v5 03/12] nbd: Utilize QAPI_CLONE for type conversion

[Markus Armbruster <armbru@redhat.com>]

Eric Blake <eblake@redhat.com> writes:

> 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(-)
>
> diff --git a/blockdev-nbd.c b/blockdev-nbd.c
> index 8174023e5c47..cee9134b12eb 100644
> --- a/blockdev-nbd.c
> +++ b/blockdev-nbd.c
> @@ -14,6 +14,8 @@
>  #include "sysemu/block-backend.h"
>  #include "hw/block/block.h"
>  #include "qapi/error.h"
> +#include "qapi/clone-visitor.h"
> +#include "qapi/qapi-visit-block-export.h"
>  #include "qapi/qapi-commands-block-export.h"
>  #include "block/nbd.h"
>  #include "io/channel-socket.h"
> @@ -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_strdup(arg->device);
>      }

This is the fix you mentioned in the commit message.

>
>      export_opts = g_new(BlockExportOptions, 1);
> @@ -205,15 +208,9 @@ void qmp_nbd_server_add(NbdServerAddOptions *arg, Error **errp)
       *export_opts = (BlockExportOptions) {
           .type                   = BLOCK_EXPORT_TYPE_NBD,
           .id                     = g_strdup(arg->name),
>          .node_name              = g_strdup(bdrv_get_node_name(bs)),
>          .has_writable           = arg->has_writable,
>          .writable               = arg->writable,

Explicit initialization of all the common members, except for
@writethrough.  @writethrough is optional, so not mentioning it makes it
absent.  I don't mind.

> -        .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),

Explicit initialization of all the variant members: copy of @arg.

> -        },
>      };
> +    QAPI_CLONE_MEMBERS(BlockExportOptionsNbd, &export_opts->u.nbd,
> +                       qapi_NbdServerAddOptions_base(arg));

Another (and better) way to copy.

>
>      /*
>       * nbd-server-add doesn't complain when a read-only device should be

Reviewed-by: Markus Armbruster <armbru@redhat.com>