Re: [PATCH v3 1/2] migration: Fix incorrect integer->float conversion caught by clang

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 11/22/19 9:00 AM, Markus Armbruster wrote:
> From: Fangrui Song <i@maskray.me>
> 
> Clang does not like qmp_migrate_set_downtime()'s code to clamp double
> @value to 0..INT64_MAX:
> 
>      qemu/migration/migration.c:2038:24: error: implicit conversion from 'long' to 'double' changes value from 9223372036854775807 to 9223372036854775808 [-Werror,-Wimplicit-int-float-conversion]
> 
> The warning will be enabled by default in clang 10. It is not
> available for clang <= 9.
> 
> The clamp is actually useless; @value is checked to be within
> 0..MAX_MIGRATE_DOWNTIME_SECONDS immediately before.  Delete it.
> 
> While there, make the conversion from double to int64_t explicit.
> 
> Signed-off-by: Fangrui Song <i@maskray.me>
> Reviewed-by: Markus Armbruster <armbru@redhat.com>
> [Patch split, commit message improved]
> Signed-off-by: Markus Armbruster <armbru@redhat.com>
> ---
>   migration/migration.c | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/migration/migration.c b/migration/migration.c
> index 354ad072fa..09b150663f 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -2035,11 +2035,10 @@ void qmp_migrate_set_downtime(double value, Error **errp)
>       }
>   
>       value *= 1000; /* Convert to milliseconds */
> -    value = MAX(0, MIN(INT64_MAX, value));
>   
>       MigrateSetParameters p = {
>           .has_downtime_limit = true,
> -        .downtime_limit = value,
> +        .downtime_limit = (int64_t)value,

I agree with Eric a one line comment about the explicit cast is 
welcomed. We can still use 'git blame', find the last commit sha, then 
look at the commit description. But having it along the code is 
straightforward.

Preferably with a comment (the maintainer queing this can amend it):
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>

>       };
>   
>       qmp_migrate_set_parameters(&p, errp);
>