linux-kernel - Re: [RFC][4/11][MANUX] Kernel compatibility : ioctl(2)

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Message-ID: <20140415160035.3135dda7@alan.etchedpixels.co.uk>
Date:	Tue, 15 Apr 2014 16:00:35 +0100
From:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
To:	Emmanuel Colbus <ecolbus@...ux.info>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [RFC][4/11][MANUX] Kernel compatibility : ioctl(2)

On Tue, 15 Apr 2014 15:42:54 +0200
Emmanuel Colbus <ecolbus@...ux.info> wrote:

> Continuing with syscalls, I would like to indicate you a modification
> I've done with regards to ioctl's. The thing is, I have had the need for
> ioctl's that return *file descriptors*, instead of standard return codes.

You probably only think you have ;-)

The return from an ioctl on 32bit is going to be an unsigned 32bit value,
as is a Linux file handle. So if you do

	fd = ioctl(foo);

then not only have you got an interface that isn't compliant with
POSIX/SuS you also have no error reporting capability.

The expectation of ioctl is

	err = ioctl(fd, FDIOWIBBLE, &result);

now if result is a pointer to where to store one or more file handles you
are sorted.

If you are going to use SuS/POSIX naming I'd really suggest sticking to
the expected behaviour in the standards.

Alan
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