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Date:   Thu, 22 Sep 2022 16:05:04 +0200
From:   Petr =?utf-8?Q?=C5=A0tetiar?= <ynezz@true.cz>
To:     Phil Auld <pauld@redhat.com>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org, yury.norov@gmail.com,
        rafael@kernel.org
Subject: Re: aarch64 5.15.68 regression in topology/thread_siblings (huge
 file size and no content)
Message-ID: <20220922140504.GA58265@meh.true.cz>
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Phil Auld <pauld@redhat.com> [2022-09-22 09:18:47]:

Hi,

> I've seen the size cause problems for tools. Are we sure that it's the empty file and not
> the size causing issues?  Maybe something is treating that as signed again for a count of
> -1 bytes (which seems like it would be a bug anyway)?

  root@OpenWrt:/# strace cat /sys/devices/system/cpu/cpu1/topology/thread_siblings
  ...snip...
  openat(AT_FDCWD, "/sys/devices/system/cpu/cpu1/topology/thread_siblings", O_RDONLY|O_LARGEFILE) = 3
  sendfile(1, 3, NULL, 16777216)          = 0

  root@OpenWrt:/# strace md5sum /sys/devices/system/cpu/cpu1/topology/thread_sibli
  ...snip...
  openat(AT_FDCWD, "/sys/devices/system/cpu/cpu1/topology/thread_siblings", O_RDONLY|O_LARGEFILE) = 3
  read(3, "", 4096)                       = 0

  root@OpenWrt:/# strace head /sys/devices/system/cpu/cpu1/topology/thread_siblings
  ...snip...
  openat(AT_FDCWD, "/sys/devices/system/cpu/cpu1/topology/thread_siblings", O_RDONLY|O_LARGEFILE) = 3
  read(3, "", 1024)                       = 0

Cheers,

Petr