linux-kernel - Re: [PATCH] mm/hugetlb: use EOPNOTSUPP in hugetlb sysctl handlers

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Message-Id: <20160307160359.c8cde2e7cc4a52234f212c0d@linux-foundation.org>
Date:	Mon, 7 Mar 2016 16:03:59 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jan Stancek <jstancek@...hat.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	n-horiguchi@...jp.nec.com, mike kravetz <mike.kravetz@...cle.com>,
	hillf zj <hillf.zj@...baba-inc.com>,
	kirill shutemov <kirill.shutemov@...ux.intel.com>,
	dave hansen <dave.hansen@...ux.intel.com>,
	paul gortmaker <paul.gortmaker@...driver.com>
Subject: Re: [PATCH] mm/hugetlb: use EOPNOTSUPP in hugetlb sysctl handlers

On Sat, 5 Mar 2016 03:09:50 -0500 (EST) Jan Stancek <jstancek@...hat.com> wrote:

> > > Replace ENOTSUPP with EOPNOTSUPP. If hugepages are not supported,
> > > this value is propagated to userspace. EOPNOTSUPP is part of uapi
> > > and is widely supported by libc libraries.
> > 
> > hm, what is the actual user-visible effect of this change?  Does it fix
> > some misbehaviour?
> > 
> 
> It gives nicer message to user, rather than:
> # cat /proc/sys/vm/nr_hugepages
> cat: /proc/sys/vm/nr_hugepages: Unknown error 524
> 
> And also LTP's proc01 test was failing because this ret code (524)
> was unexpected:
> proc01      1  TFAIL  :  proc01.c:396: read failed: /proc/sys/vm/nr_hugepages: errno=???(524): Unknown error 524
> proc01      2  TFAIL  :  proc01.c:396: read failed: /proc/sys/vm/nr_hugepages_mempolicy: errno=???(524): Unknown error 524
> proc01      3  TFAIL  :  proc01.c:396: read failed: /proc/sys/vm/nr_overcommit_hugepages: errno=???(524): Unknown error 524
> 

Ah, OK, thanks.  "Unknown error 524" is rather rude.  I'll queue this
for 4.5.