Re: [Qemu-devel] [PATCH v2 1/2] migration: allow clearing migration string parameters

[Eric Blake]

On 03/02/2017 06:37 AM, Daniel P. Berrange wrote:
> Some of the migration parameters are strings, which default to NULL,
> eg tls-hostname and tls-creds.
> 
> The mgmt app will set the tls-creds parameter on both source and target
> QEMU instances, in order to trigger use of TLS for migration.
> 
> After performing a TLS encrypted migration though, migration might be
> used for other reasons - for example, to save the QEMU state to a file.
> We need TLS turned off when doing this, but the migrate-set-parameters
> QAPI command does not provide any facility to clear/reset parameters
> to their default state.
> 
> If you simply omit the tls_creds parameter in migrate-set-parameters,
> then 'has_tls_creds' will be false and so no action will be taken. JSON
> allows a parameter to have a nil value, but the QEMU JSON visitor will
> reject that when deserializing into a QObject.
> 
> The migration code has no need to distinguish "" vs NULL for the TLS
> hostname or TLS credentials object name, since "" is invalid in both
> cases. This enables clearing of tls-hostname and tls-creds by
> treating "" as equivalent to NULL.

It's also worth documenting in the .json file that "" is special-cased.
But the C code change looks okay (with your explanation on v1 that the
has_* parameters are not used internally).

> 
> Signed-off-by: Daniel P. Berrange <address@hidden>
> ---
>  migration/migration.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/migration/migration.c b/migration/migration.c
> index c6ae69d..a8cb56e 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -872,11 +872,19 @@ void qmp_migrate_set_parameters(MigrationParameters 
> *params, Error **errp)
>      }
>      if (params->has_tls_creds) {
>          g_free(s->parameters.tls_creds);
> -        s->parameters.tls_creds = g_strdup(params->tls_creds);
> +        if (*params->tls_creds == '\0') {
> +            s->parameters.tls_creds = NULL;
> +        } else {
> +            s->parameters.tls_creds = g_strdup(params->tls_creds);
> +        }
>      }
>      if (params->has_tls_hostname) {
>          g_free(s->parameters.tls_hostname);
> -        s->parameters.tls_hostname = g_strdup(params->tls_hostname);
> +        if (*params->tls_hostname == '\0') {
> +            s->parameters.tls_hostname = NULL;
> +        } else {
> +            s->parameters.tls_hostname = g_strdup(params->tls_hostname);
> +        }
>      }
>      if (params->has_max_bandwidth) {
>          s->parameters.max_bandwidth = params->max_bandwidth;
> 

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

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