Re: [PATCH v8 2/2] xenpm: Add get-core-temp subcommand

[Jan Beulich <jbeulich@xxxxxxxx>]

On 27.02.2026 18:00, Teddy Astie wrote:
> @@ -1354,6 +1358,127 @@ void enable_turbo_mode(int argc, char *argv[])
>                  errno, strerror(errno));
>  }
>  
> +static int fetch_dts_temp(xc_interface *xch, uint32_t cpu, bool package, int 
> *temp)
> +{
> +    xc_resource_entry_t entries[] = {
> +        { .idx = package ? MSR_PACKAGE_THERM_STATUS : MSR_IA32_THERM_STATUS 
> },
> +        { .idx = MSR_TEMPERATURE_TARGET },
> +    };
> +    struct xc_resource_op ops = {
> +        .cpu = cpu,
> +        .entries = entries,
> +        .nr_entries = ARRAY_SIZE(entries),
> +    };
> +    int tjmax;
> +
> +    int ret = xc_resource_op(xch, 1, &ops);
> +
> +    switch ( ret )
> +    {
> +    case 0:
> +        /* This CPU isn't online or can't query this MSR */
> +        return -1;

Further down at the callers of this function you assume errno is set whenever
an error indication is returned. As xc_resource_op() didn't fail, you will
need to synthesize an errno value here.

> +static void get_core_temp(int argc, char *argv[])
> +{
> +    int temp = -1, cpu = -1;
> +    unsigned int socket;
> +    bool has_data = false;
> +
> +    if ( argc > 0 )
> +        parse_cpuid(argv[0], &cpu);
> +
> +    if ( cpu != -1 )
> +    {
> +        if ( !fetch_dts_temp(xc_handle, cpu, false, &temp) )
> +            printf("CPU%d: %d°C\n", cpu, temp);
> +        else
> +        {
> +            fprintf(stderr, "Unable to fetch temperature (%d - %s)\n",
> +                    errno, strerror(errno));
> +            printf("No data\n");
> +            exit(ENODATA);

In how far is using errno values as arguments to exit() a useful thing? (I
think you had it like this before, and I merely forgot to ask.) Yes, I can
see the tool using a number of exit(EINVAL), but I don't understand those
either. This way you can't even document easily what particular exit codes
mean, as the errno values may vary across OSes.

Jan