linux-kernel - Re: [PATCH] tools/power turbostat: Fix MSRs with CONFIG

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Message-ID: <99f09d35e30fa335508823e9848a3365936ac9b3.camel@intel.com>
Date: Mon, 16 Jun 2025 01:30:25 +0000
From: "Zhang, Rui" <rui.zhang@...el.com>
To: "calvin@...nvd.org" <calvin@...nvd.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
CC: "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>, "lenb@...nel.org"
	<lenb@...nel.org>
Subject: Re: [PATCH] tools/power turbostat: Fix MSRs with CONFIG_MULTIUSER=n

On Fri, 2025-06-13 at 19:20 -0700, Calvin Owens wrote:
> Handle ENOSYS from cap_get_proc() in check_for_cap_sys_rawio(), so
> turbostat can display temperatures when running on kernels compiled
> without multiuser support.
> 
> Signed-off-by: Calvin Owens <calvin@...nvd.org>
> ---
>  tools/power/x86/turbostat/turbostat.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/power/x86/turbostat/turbostat.c
> b/tools/power/x86/turbostat/turbostat.c
> index 925556b90770..f7d665913a52 100644
> --- a/tools/power/x86/turbostat/turbostat.c
> +++ b/tools/power/x86/turbostat/turbostat.c
> @@ -6496,8 +6496,13 @@ int check_for_cap_sys_rawio(void)
>  	int ret = 0;
>  
>  	caps = cap_get_proc();
> -	if (caps == NULL)
> +	if (caps == NULL) {
> +		/* Support CONFIG_MULTIUSER=n */
> +		if (errno == ENOSYS)

Can you point me where this knowledge comes from?

I downloaded the libcap source and didn't see how ENOSYS is set.

thanks,
rui
> +			return 0;
> +
>  		return 1;
> +	}
>  
>  	if (cap_get_flag(caps, CAP_SYS_RAWIO, CAP_EFFECTIVE,
> &cap_flag_value)) {
>  		ret = 1;