linux-kernel - Re: about ENOSYS

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Date:	Mon, 3 Aug 2015 09:21:58 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	"Drokin, Oleg" <oleg.drokin@...el.com>
Cc:	Shraddha Barke <shraddha.6596@...il.com>,
	"<devel@...verdev.osuosl.org> SUBSYSTEM" <devel@...verdev.osuosl.org>,
	"Dilger, Andreas" <andreas.dilger@...el.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"HPDD-discuss@...ts.01.org" <HPDD-discuss@...ts.01.org>,
	Julia Lawall <Julia.Lawall@...6.fr>,
	Al Viro <viro@...iv.linux.org.uk>,
	"Hammond, John" <john.hammond@...el.com>,
	Frank Zago <fzago@...y.com>
Subject: Re: about ENOSYS

On Mon, Aug 03, 2015 at 06:41:22AM +0000, Drokin, Oleg wrote:
> subject have been missing, so I filled in something.
> 
> On Aug 3, 2015, at 2:18 AM, Shraddha Barke wrote:
> 
> > From b67c6c20455b04b77447ab4561e44f1a75dd978d Mon Sep 17 00:00:00 2001
> > From: Shraddha Barke <shraddha.6596@...il.com>
> > Date: Mon, 3 Aug 2015 11:34:19 +0530
> > Subject: [PATCH] Staging : lustre : Use -EINVAL instead of -ENOSYS
> > 
> > ENOSYS means that a nonexistent system call was called. This should
> > not be used for invalid operations on otherwise valid syscalls.
> > 
> > Use -EINVAL instead of -ENOSYS. This fixes checkpatch warning message:
> > 
> > WARNING: ENOSYS means 'invalid syscall nr' and nothing else
> 
> Is this really true, though?
> I know you are working off what the tool reports.
> But in reality people have been using ENOSYS to indicate
> "this thing that you want is not really available" 
> Reading the define file we can see:
> /usr/include/asm-generic/errno.h:#define	ENOSYS		38	/* Function not implemented */
> 
> $ grep -r 'ENOSYS;' fs/ | wc -l
> 75
> 
> So it's extensively used in the fs tree by existing code.
> 
> Hmm…. Searching some more I arrived at commit e15f431f
> that changes the in-kernel comment and claims the "system call only stuff".
> 
> So Greg, do you want Lustre to get rid of use of ENOSYS (all 16 users we have),
> or is it ok to leave them in?

For now I'd just leave it as-is.
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