linux-kernel - Re: Why is CONFIG

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Date:	Sat, 11 Jun 2011 00:38:26 +0200 (CEST)
From:	Jesper Juhl <jj@...osbits.net>
To:	Al Viro <viro@...IV.linux.org.uk>
cc:	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jonas Gorski <jonas.gorski@...il.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Subject: Re: Why is CONFIG_FHANDLE an option??

On Fri, 10 Jun 2011, Al Viro wrote:

> On Sat, Jun 11, 2011 at 12:14:02AM +0200, Jesper Juhl wrote:
> > Hello
> > 
> > I just configured a new kernel based on a recent git checkout and when I 
> > had copied in my old configuration and did a "make oldconfig"I was greeted 
> > with
> > 
> >     open by fhandle syscalls (FHANDLE) [N/y/?] (NEW)
> > 
> > Ok, so I read the help text description and learn that it's about two new 
> > syscalls - open_by_handle_at(2) and name_to_handle_at(2).
> > 
> > My first thought at this point was "why are new syscalls even an option"?
> > 
> > Syscalls are in my oppinion ABI - having optional syscalls is just about 
> > as bad as removing a syscall. It basically means that users cannot know if 
> > the syscall is there and will need to test (it's bad enough having to 
> > check the kernel version, having to check for specific syscalls as well 
> > is just, well, annoying at best). 
> > 
> > Why are we making these optional?
> 
> Why not?  Software needs to test *anyway*, since it might run on earlier
> kernels.  And "does that syscall return -ENOSYS" is self-documenting,
> while "is the version higher than $MAGIC_NUMBER" is *not*.  Especially since
> there's such thing as backports.
> 
> If you need to check that syscall is there, _check_ _it_.  Don't breed
> dependencies on version numbers.

Well, sometimes you may want to make it a requirement that whomever 
deploys your software runs Linux X.Y.Z or whatever.. You don't want to 
make it "run Linux X.Y.Z with syscalls A, B, C enabled" etc.

Sometimes it's nice to draw lines in sand and just say "from this day 
forward we support so and so".


-- 
Jesper Juhl <jj@...osbits.net>       http://www.chaosbits.net/
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