[libvirt] [libvirt-go PATCH 2/2] Introduce DomainMigrateMaxSpeedFlags constant

[Daniel P. Berrangé]

On Mon, Feb 11, 2019 at 04:11:55PM +0100, Erik Skultety wrote:
> Also enforce the enum type for MigrateSetMaxSpeed and MigrateGetMaxSpeed
> functions which previously accepted generic uint32 type since the flags
> haven't been in use.

FWIW, Erik asked me about this change off-list.

Technically changing the flags parameter from uint32 to the named
enum type is considered an API incompatible change. In practice
though, the flags parameter was unused in the past, so applications
should normally have been passing an untyped '0' inline.eg

   dom.MigrateSetMaxSpeed(1024*1024, 0)

Go will happily do type inference there, so with this change it will
simply interpret '0' as being a value in the enum type. There should
not be any compile breakage in this case.

Where it could be a problem is if the app used an intermediate typed
variable

  var flags uint32
  flags = 0
  dom.MigrateSetMaxSpeed(1024*1024, flags)

This could conceivably affect some app, but I think it is fairly
unlikely since there's no compelling reason for the app to have used
a variable for flags given that it was unused. On balance with previous
cases like this I took the view that it is preferrable to change the
enum type so we get better type checking over the long term, despite
this small risk/

> 
> Signed-off-by: Erik Skultety <eskultet at redhat.com>
> ---
>  domain.go       | 10 ++++++++--
>  domain_compat.h |  4 ++++
>  2 files changed, 12 insertions(+), 2 deletions(-)

Reviewed-by: Daniel P. Berrangé <berrange at redhat.com>


Regards,
Daniel
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