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

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Message-ID: <1892529.CzZLJuFW6x@vostro.rjw.lan>
Date:	Thu, 27 Nov 2014 21:56:56 +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 09:24:30 PM Pali Rohár wrote:
> On Thursday 27 November 2014 21:39:42 Rafael J. Wysocki wrote:
> > 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:,0000,0001,0002,0
> > > 003,0004,0005,0=
> > > 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".
> > 
> 
> Ok. But why that inconsistency (missing MODALIAS line)?
> 
> > > 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.
> > 
> 
> $ cat /sys/devices/system/cpu/cpu0/modalias
> cat: /sys/devices/system/cpu/cpu0/modalias: No such file or 
> directory
> $ cat /sys/devices/system/cpu/cpu0/uevent 
> DRIVER=processor
> MODALIAS=cpu:type:x86,ven0000fam0006mod003C:feature:,0000,0001,0002,0003,0004,0005,0006,0007,0008,0009,000B,000C,000D,000E,000F,0010,0011,0013,0015,0016,0017,0018,0019,001A,001B,001C,001D,001F,002B,0034,003A,003B,003D,0068,006B,006C,006D,006F,0070,0072,0074,0075,0076,0078,007C,007D,0080,0081,0082,0083,0084,0085,0086,0087,0088,0089,008B,008C,008D,008E,008F,0091,0093,0094,0095,0096,0097,0098,0099,009A,009B,009C,009D,009E,00C0,00C5,00E0,00E1,00E3,00E5,00E6,00E7,0100,0101,0102,0103,0104,0120,0121,0123,0124,0125,0127,0128,0129,012A,012B,012D,0140
> 
> So there is no modalias file, but uevent contains MODALIAS line.
> 
> > > 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.
> 
> Yes, I know. For some reasons coretemp.ko is not automatically 
> loaded. I do not know why and I started investigating it. And I 
> found above inconsistency in modalias and uevent...
> 
> $ modinfo coretemp
> ...
> alias:          cpu:type:x86,ven0000fam*mod*:feature:*00E7*

That may be a udev issue.  See

http://lists.freedesktop.org/archives/systemd-devel/2013-July/012165.html

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