linux-kernel - Re: [PATCH 1/2] CPU, NUMA topology ABIs: clarify the overflow issue of sysfs pagebuf

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Date:   Fri, 30 Apr 2021 08:05:45 +0200
From:   "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     "Song Bao Hua (Barry Song)" <song.bao.hua@...ilicon.com>,
        "tiantao (H)" <tiantao6@...ilicon.com>,
        "corbet@....net" <corbet@....net>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>
Subject: Re: [PATCH 1/2] CPU, NUMA topology ABIs: clarify the overflow issue
 of sysfs pagebuf

On Thu, Apr 29, 2021 at 03:38:39PM -0700, Dave Hansen wrote:
> On 4/29/21 3:32 PM, Song Bao Hua (Barry Song) wrote:
> > $ strace numactl --hardware  2>&1 | grep cpu
> > openat(AT_FDCWD, "/sys/devices/system/cpu",
> > O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3
> > openat(AT_FDCWD, "/sys/devices/system/node/node0/cpumap", O_RDONLY) = 3
> > openat(AT_FDCWD, "/sys/devices/system/node/node1/cpumap", O_RDONLY) = 3
> > openat(AT_FDCWD, "/sys/devices/system/node/node2/cpumap", O_RDONLY) = 3
> > openat(AT_FDCWD, "/sys/devices/system/node/node3/cpumap", O_RDONLY) = 3
> > 
> > If we move to binary, it means we have to change those applications.
> 
> I thought Greg was saying to using a sysfs binary attribute using
> something like like sysfs_create_bin_file().  Those don't have the
> PAGE_SIZE limitation.  But, there's also nothing to keep us from spewing
> nice human-readable text via the "binary" file.

That is correct.