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

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Date:	Sat, 5 Mar 2016 03:09:50 -0500 (EST)
From:	Jan Stancek <jstancek@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
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





----- Original Message -----
> 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>
> Sent: Friday, 4 March, 2016 10:38:07 PM
> Subject: Re: [PATCH] mm/hugetlb: use EOPNOTSUPP in hugetlb sysctl handlers
> 
> On Thu,  3 Mar 2016 11:02:51 +0100 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

Regards,
Jan