linux-kernel - Re: [PATCH 1/1] drivers/base/cpu: Print kernel arch

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Date:   Thu, 28 Jul 2022 09:35:11 +0200
From:   Petr Vorel <pvorel@...e.cz>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        David Sterba <dsterba@...e.com>
Subject: Re: [PATCH 1/1] drivers/base/cpu: Print kernel arch

> On Thu, Jul 28, 2022 at 12:22:05AM +0200, Petr Vorel wrote:
> > Hi Greg,

> > thanks for your review!

> > > On Wed, Jul 27, 2022 at 06:11:35PM +0200, Petr Vorel wrote:
> > > > Print kernel architecture in /sys/devices/system/cpu/arch
> > > > using UTS_MACHINE, i.e. member of struct uts_namespace.machine.

> > > > This helps people who debug kernel with initramfs with minimal
> > > > environment (i.e. without coreutils or even busybox) or allow to open
> > > > sysfs file instead of run uname -m in high level languages.

> > > > Signed-off-by: Petr Vorel <pvorel@...e.cz>
> > > > ---
> > > >  drivers/base/cpu.c | 9 +++++++++
> > > >  1 file changed, 9 insertions(+)

> > > You can't add a new sysfs file without a Documentation/ABI/ update as
> > > well.  Please fix that up.
> > I'm sorry. Yes, I realized it later on (once I got offline).
> > Sure, I'll fix this in v2. But the main question is whether this feature is
> > acceptable and what is the best place for the file.


> > > > diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
> > > > index 4c98849577d4..7c8032e3ff10 100644
> > > > --- a/drivers/base/cpu.c
> > > > +++ b/drivers/base/cpu.c
> > > > @@ -3,6 +3,7 @@
> > > >   * CPU subsystem support
> > > >   */

> > > > +#include <generated/compile.h>
> > > >  #include <linux/kernel.h>
> > > >  #include <linux/module.h>
> > > >  #include <linux/init.h>
> > > > @@ -232,6 +233,13 @@ static ssize_t print_cpus_kernel_max(struct device *dev,
> > > >  }
> > > >  static DEVICE_ATTR(kernel_max, 0444, print_cpus_kernel_max, NULL);

> > > > +static ssize_t print_cpus_arch(struct device *dev,
> > > > +				     struct device_attribute *attr, char *buf)
> > > > +{
> > > > +	return sysfs_emit(buf, "%s\n", UTS_MACHINE);
> > > > +}
> > > > +static DEVICE_ATTR(arch, 0444, print_cpus_arch, NULL);

> > > why just UTS_MACHINE?  Doesn't 'uname' show this already?  And I thought
> > > this was in /proc/cpuinfo but odd, it isn't...
> > Sure, this info is in uname(). But for certain cases is really easier to read
> > file from /proc or /sys than run create custom C bindings or a binary which
> > calls uname(2) libc wrapper or run uname binary via execve(2).

> > Yes, I also expected /proc/cpuinfo would have it but it does not have it. I
> > don't think it's a good idea to add 'arch  : foo' line to it, but I can do if
> > there is consensus that it's the best place.

> > > Also what about the other things in compile.h?
> > UTS_VERSION is in /proc/version.
> > LINUX_COMPILE_BY (e.g. "user"), LINUX_COMPILE_HOST (e.g. "host") and
> > LINUX_COMPILER (e.g. "aarch64-alpine-linux-musl-gcc (Alpine 11.2.1_git20220219)
> > ...") are IMHO useless, but I can add it if you wish.

> > Well, there is hostname in /proc/sys/kernel/hostname, there are also ostype and
> > osrelease.. Thinking about it twice /proc/sys/kernel/ looks to me a better place
> > for arch file than current /sys/devices/system/cpu/. WDYT?

> Yeah, I think /proc/sys/kernel/ makes sense, good idea.
Thanks for info, I'll send v2 shortly.

Kind regards,
Petr

> greg k-h