linux-kernel - Re: Missing MODALIAS in /sys/devices/system/cpu/uevent

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Message-ID: <1716071.jpYXuFBQgb@vostro.rjw.lan>
Date:	Thu, 27 Nov 2014 21:39:42 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Pali Rohár <pali.rohar@...il.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Len Brown <lenb@...nel.org>, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: Missing MODALIAS in /sys/devices/system/cpu/uevent

On Thursday, November 27, 2014 09:01:11 PM Pali Rohár wrote:
> 
> --nextPart2712852.Yg3XtZvm05
> Content-Type: Text/Plain;
>   charset="utf-8"
> Content-Transfer-Encoding: quoted-printable
> 
> Hello,
> 
> on 3.18-rc5 I have empty cpu uevent file, but modalias file is=20
> populated. See:
> 
> $ cat /sys/devices/system/cpu/uevent=20
> $ cat /sys/devices/system/cpu/modalias=20
> cpu:type:x86,ven0000fam0006mod003C:feature:,0000,0001,0002,0003,0004,0005,0=
> 006,0007,0008,0009,000B,000C,000D,000E,000F,0010,0011,0013,0015,0016,0017,0=
> 018,0019,001A,001B,001C,001D,001F,002B,0034,003A,003B,003D,0068,006B,006C,0=
> 06D,006F,0070,0072,0074,0075,0076,0078,007C,007D,0080,0081,0082,0083,0084,0=
> 085,0086,0087,0088,0089,008B,008C,008D,008E,008F,0091,0093,0094,0095,0096,0=
> 097,0098,0099,009A,009B,009C,009D,009E,00C0,00C5,00E0,00E1,00E3,00E5,00E6,0=
> 0E7,0100,0101,0102,0103,0104,0120,0121,0123,0124,0125,0127,0128,0129,012A,0=
> 12B,012D,0140
> 
> =46or all other devices in /sys/devices/ which have modalias=20
> content there is also MODALIAS=3D line in uevent file.

/sys/devices/system/cpu/ is not a device.  It is a "collection of all CPUs".

> Is cpu device special? Or why it is only one device which has=20
> modalias file but is missing MODALIAS=3D line in uevent file?

Look into the uevent files under /sys/devices/system/cpu/cpu0/ etc.

> What userspace application should use for reading modalias=20
> string? File modalias or file uevent?

The cpu modalias is used to trigger loading of some CPU-specific modules
upfront IIRC.  So yes, it is special.

My advice would be to follow udev here.


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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