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

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Message-ID: <fd78ac30-dd3b-a7d7-eae8-193b09a7d49a@intel.com>
Date:   Thu, 29 Apr 2021 15:38:39 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Song Bao Hua (Barry Song)" <song.bao.hua@...ilicon.com>,
        "tiantao (H)" <tiantao6@...ilicon.com>,
        "corbet@....net" <corbet@....net>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
Cc:     "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 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.

We don't need to change the file format, just the internal kernel API
that we produce the files with.