[libvirt] [PATCH 3/3] libvirt-domain: virConnectListDomains: Return 0 on zero-size buffer

[Daniel P. Berrangé]

On Mon, Nov 18, 2019 at 01:18:19PM +0100, Erik Skultety wrote:
> It doesn't make sense to pass a target buffer into an API, declaring its
> size as 0 and expect some meaningful result. Since this used to work
> pre-Glib era, we shouldn't end with an error, but we can return 0
> for the number of domains immediately, instead of calling into the
> daemon, which is exactly what the daemon would have returned anyway.

Passing in size as 0 is going to be normal practice, given the calling
convention of this API design. 

> 
> Signed-off-by: Erik Skultety <eskultet at redhat.com>
> ---
>  src/libvirt-domain.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/src/libvirt-domain.c b/src/libvirt-domain.c
> index 02622cb2ca..0def40fdf7 100644
> --- a/src/libvirt-domain.c
> +++ b/src/libvirt-domain.c
> @@ -62,6 +62,9 @@ virConnectListDomains(virConnectPtr conn, int *ids, int maxids)
>      virCheckNonNullArgGoto(ids, error);
>      virCheckNonNegativeArgGoto(maxids, error);
>  
> +    if (maxids == 0)
> +        return 0;

This is too late really, as we alrady checked 'ids'.

IMHO, we should only mandate a non-NULL 'ids' parameter when
maxids > 0 a few lines earlier

All the other legacy APIs share the same validation flaw so will
also need fixing.

Regards,
Daniel
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