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Date: Fri, 10 Jun 2011 23:47:38 +0100
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Jesper Juhl <jj@chaosbits.net>
Cc: linux-kernel@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Jonas Gorski <jonas.gorski@gmail.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Subject: Re: Why is CONFIG_FHANDLE an option??
Message-ID: <20110610224738.GB11521@ZenIV.linux.org.uk>
References: <alpine.LNX.2.00.1106110001180.21722@swampdragon.chaosbits.net>
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On Fri, Jun 10, 2011 at 11:39:55PM +0100, Al Viro wrote:

> 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.

PS: we have BSD_PROCESS_ACCT doing pretty much the same kind of thing.
And SYSVIPC.  And POSIX_MQUEUE.  And there's nfsservctl(2), also
config-dependent.  And eventfd(2), and inotify syscalls, etc.

There is such thing as optional system calls.  Always had been.  Deal
with that...