Re: [Qemu-devel] [PATCH for-2.4 2/2] qom: Fix invalid error check in property_get_str()

[Eric Blake <eblake@redhat.com>]

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On 07/01/2015 09:47 AM, Markus Armbruster wrote:
> When a function returns a null pointer on error and only on error, you
> can do
> 
>     if (!foo(foos, errp)) {
>         ... handle error ...
>     }
> 
> instead of the more cumbersome
> 
>     Error *err = NULL;
> 
>     if (!foo(foos, &err)) {
>         error_propagate(errp, err);
>         ... handle error ...
>     }
> 
> A StringProperty's getter, however, may return null on success!  We
> then fail to call visit_type_str().
> 
> Screwed up in 6a146eb, v1.1.
> 
> Fails tests/qom-test in my current, heavily hacked QAPI branch.  No
> reproducer for master known (but I didn't look hard).
> 
> Cc: Andreas Färber <afaerber@suse.de>
> Cc: Anthony Liguori <aliguori@us.ibm.com>
> Signed-off-by: Markus Armbruster <armbru@redhat.com>
> ---
>  qom/object.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 

Reviewed-by: Eric Blake <eblake@redhat.com>

> diff --git a/qom/object.c b/qom/object.c
> index 6173da8..4c4df55 100644
> --- a/qom/object.c
> +++ b/qom/object.c
> @@ -1591,14 +1591,18 @@ typedef struct StringProperty
>  static void property_get_str(Object *obj, Visitor *v, void *opaque,
>                               const char *name, Error **errp)
>  {
> +    Error *err = NULL;
>      StringProperty *prop = opaque;
>      char *value;
>  
> -    value = prop->get(obj, errp);
> -    if (value) {
> -        visit_type_str(v, &value, name, errp);
> -        g_free(value);
> +    value = prop->get(obj, &err);
> +    if (err) {
> +        error_propagate(errp, err);
> +        return;
>      }
> +
> +    visit_type_str(v, &value, name, errp);
> +    g_free(value);
>  }
>  
>  static void property_set_str(Object *obj, Visitor *v, void *opaque,
> 

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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