Re: [PATCH v5 2/2] xenpm: Add get-intel-temp subcommand

[Jan Beulich <jbeulich@xxxxxxxx>]

On 12.01.2026 17:47, Teddy Astie wrote:
> @@ -1354,6 +1358,115 @@ 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 -1:
> +        /* xc_resource_op returns -1 in out of memory scenarios */
> +        return -ENOMEM;

Assuming xc_resource_op() is well-behaved in this regard, why not return errno
here? Or yet better stick to -1, leaving it to the caller to consume errno? And
then ...

> +    case 0:
> +        /* This CPU isn't online or can't query this MSR */
> +        return -ENODATA;

... set errno here and return -1? With this normalized here, ...

> +    case 1:
> +    {
> +        /*
> +         * The CPU doesn't support MSR_TEMPERATURE_TARGET, we assume it's 100
> +         * which is correct aside a few selected Atom CPUs. Check Linux
> +         * kernel's coretemp.c for more information.
> +         */
> +        static bool has_reported_once = false;
> +
> +        if ( !has_reported_once )
> +        {
> +            fprintf(stderr, "MSR_TEMPERATURE_TARGET is not supported, assume 
> "
> +                            "tjmax = 100, readings may be incorrect.\n");
> +            has_reported_once = true;
> +        }
> +
> +        tjmax = 100;
> +        break;
> +    }
> +
> +    case 2:
> +        tjmax = (entries[1].val >> 16) & 0xff;
> +        break;
> +
> +    default:
> +        if ( ret > 0 )
> +        {
> +            fprintf(stderr, "Got unexpected xc_resource_op return value: %d",
> +                    ret);
> +            return -EINVAL;
> +        }
> +        return ret;
> +    }
> +
> +    *temp = tjmax - ((entries[0].val >> 16) & 0xff);
> +    return 0;
> +}
> +
> +static void get_intel_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
> +            printf("No data\n");

... you can then use perror() here (and perhaps elsewhere). Right now the
distinct non-zero return values of fetch_dts_temp() are of no interest to
any of the callers.

Jan