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From: "Ahmed S. Darwish" <darwish.07@gmail.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: arnd@arndb.de, ebiederm@xmission.com, gnomes@lxorguk.ukuu.org.uk,
	teg@jklm.no, jkosina@suse.cz, luto@amacapital.net,
	linux-api@vger.kernel.org, linux-kernel@vger.kernel.org,
	daniel@zonque.or, dh.herrmann@gmail.com, tixxdz@opendz.org,
	"Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Daniel Mack <daniel@zonque.org>
Subject: Re: [PATCH 01/13] kdbus: add documentation
Date: Sun, 25 Jan 2015 05:30:50 +0200
Message-ID: <20150125033050.GC6621@Darwish.PC> (raw)
In-Reply-To: <20150123131946.GA26302@kroah.com>

On Fri, Jan 23, 2015 at 09:19:46PM +0800, Greg Kroah-Hartman wrote:
> On Fri, Jan 23, 2015 at 08:28:20AM +0200, Ahmed S. Darwish wrote:
> > On Fri, Jan 16, 2015 at 11:16:05AM -0800, Greg Kroah-Hartman wrote:
> > > From: Daniel Mack <daniel@zonque.org>
> > > 
> > > kdbus is a system for low-latency, low-overhead, easy to use
> > > interprocess communication (IPC).
> > > 
> > > The interface to all functions in this driver is implemented via ioctls
> > > on files exposed through a filesystem called 'kdbusfs'. The default
> > > mount point of kdbusfs is /sys/fs/kdbus.
> > 
> > Pardon my ignorance, but we've always been told that adding
> > new ioctl()s to the kernel is a very big no-no.  But given
> > the seniority of the folks stewarding this kdbus effort,
> > there must be a good rationale ;-)
> > 
> > So, can the rationale behind introducing new ioctl()s be
> > further explained? It would be even better if it's included
> > in the documentation patch itself.
> 
> The main reason to use an ioctl is that you want to atomically set
> and/or get something "complex" through the user/kernel boundary.  For
> simple device attributes, sysfs works great, for configuring devices,
> configfs works great, but for data streams / structures / etc. an ioctl
> is the correct thing to use.
> 
> Examples of new ioctls being added to the kernel are all over the
> place, look at all of the special-purpose ioctls the filesystems keep
> creating (they aren't adding new syscalls), look at the monstrosity that
> is the DRM layer, look at other complex things like openvswitch, or
> "simpler" device-specific interfaces like the MEI one, or even more
> complex ones like the MMC interface.  These are all valid uses of ioctls
> as they are device/filesystem specific ways to interact with the kernel.
> 
> The thing is, almost no one pays attention to these new ioctls as they
> are domain-specific interfaces, with open userspace programs talking to
> them, and they work well.  ioctl is a powerful and useful interface, and
> if we were to suddenly require no new ioctls, and require everything to
> be a syscall, we would do nothing except make apis more complex (hint,
> you now have to do extra validation on your file descriptor passed to
> you to determine if it really is what you can properly operate your
> ioctl on), and cause no real benefit at all.
> 
> Yes, people abuse ioctls at times, but really, they are needed.
> 
> And remember, I was one of the people who long ago thought we should not
> be adding more ioctls, but I have seen the folly of my ways, and chalk
> it up to youthful ignorance :)
> 

Exactly, and that's why I wondered about the sudden change
of heart ;-)

Thanks for taking the time to write this.

Regards,
Darwish

  parent reply index

Thread overview: 86+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-01-16 19:16 [PATCH v3 00/13] Add kdbus implementation Greg Kroah-Hartman
2015-01-16 19:16 ` [PATCH 01/13] kdbus: add documentation Greg Kroah-Hartman
2015-01-20 13:53   ` Michael Kerrisk (man-pages)
2015-01-20 14:31     ` David Herrmann
2015-01-20 14:42       ` Josh Boyer
2015-01-20 14:53         ` Djalal Harouni
2015-01-20 16:08           ` Johannes Stezenbach
2015-01-20 17:00             ` David Herrmann
2015-01-20 22:00               ` Johannes Stezenbach
2015-01-21 10:28       ` Michael Kerrisk (man-pages)
2015-01-20 18:23     ` Daniel Mack
2015-01-21 10:32       ` Michael Kerrisk (man-pages)
2015-01-21 15:19         ` Theodore Ts'o
2015-01-21 16:58         ` Daniel Mack
2015-01-22 10:18           ` Michael Kerrisk (man-pages)
2015-01-22 13:46             ` David Herrmann
2015-01-22 14:49               ` Austin S Hemmelgarn
2015-01-23 16:08                 ` Greg Kroah-Hartman
2015-01-26 14:46                   ` Michael Kerrisk (man-pages)
2015-01-27 15:05                     ` David Herrmann
2015-01-27 16:03                       ` Andy Lutomirski
2015-01-29  8:53                         ` Daniel Mack
2015-01-29 11:25                           ` Andy Lutomirski
2015-01-29 11:42                             ` Daniel Mack
2015-01-29 12:09                               ` Andy Lutomirski
2015-02-02  9:34                                 ` Daniel Mack
2015-02-02 20:12                                   ` Andy Lutomirski
2015-02-03 10:09                                     ` Daniel Mack
2015-02-04  0:41                                       ` Andy Lutomirski
2015-02-04  2:47                                         ` Eric W. Biederman
2015-02-04  3:14                                           ` Greg Kroah-Hartman
2015-02-04  6:30                                             ` Eric W. Biederman
2015-02-04 23:03                                       ` Andy Lutomirski
2015-02-05  0:16                                         ` David Herrmann
2015-02-08 16:54                                           ` Andy Lutomirski
2015-01-27 18:03                       ` Michael Kerrisk (man-pages)
2015-01-23 11:47               ` Michael Kerrisk (man-pages)
2015-01-23 15:54             ` Greg Kroah-Hartman
2015-01-26 14:42               ` Michael Kerrisk (man-pages)
2015-01-26 15:26                 ` Tom Gundersen
2015-01-26 16:44                   ` christoph Hellwig
2015-01-26 16:45                   ` Michael Kerrisk (man-pages)
2015-01-27 15:23                     ` David Herrmann
2015-01-27 17:53                       ` Michael Kerrisk (man-pages)
2015-01-27 18:14                         ` Daniel Mack
2015-01-28 10:46                           ` Michael Kerrisk (man-pages)
2015-01-20 13:58   ` Michael Kerrisk (man-pages)
2015-01-20 17:50     ` Daniel Mack
2015-01-21  8:57       ` Michael Kerrisk (man-pages)
2015-01-21  9:07         ` Daniel Mack
2015-01-21  9:07     ` Michael Kerrisk (man-pages)
2015-01-21  9:12       ` Daniel Mack
2015-01-23  6:28   ` Ahmed S. Darwish
2015-01-23 13:19     ` Greg Kroah-Hartman
2015-01-23 13:29       ` Greg Kroah-Hartman
2015-01-25  3:30       ` Ahmed S. Darwish [this message]
2015-01-16 19:16 ` [PATCH 02/13] kdbus: add header file Greg Kroah-Hartman
2015-01-16 19:16 ` [PATCH 03/13] kdbus: add driver skeleton, ioctl entry points and utility functions Greg Kroah-Hartman
2015-01-16 19:16 ` [PATCH 04/13] kdbus: add connection pool implementation Greg Kroah-Hartman
2015-01-16 19:16 ` [PATCH 05/13] kdbus: add connection, queue handling and message validation code Greg Kroah-Hartman
2015-01-16 19:16 ` [PATCH 06/13] kdbus: add node and filesystem implementation Greg Kroah-Hartman
2015-01-16 19:16 ` [PATCH 07/13] kdbus: add code to gather metadata Greg Kroah-Hartman
2015-01-16 19:16 ` [PATCH 08/13] kdbus: add code for notifications and matches Greg Kroah-Hartman
2015-01-16 19:16 ` [PATCH 09/13] kdbus: add code for buses, domains and endpoints Greg Kroah-Hartman
2015-01-16 19:16 ` [PATCH 10/13] kdbus: add name registry implementation Greg Kroah-Hartman
2015-01-16 19:16 ` [PATCH 11/13] kdbus: add policy database implementation Greg Kroah-Hartman
2015-01-16 19:16 ` [PATCH 12/13] kdbus: add Makefile, Kconfig and MAINTAINERS entry Greg Kroah-Hartman
2015-01-16 19:16 ` [PATCH 13/13] kdbus: add selftests Greg Kroah-Hartman
2015-01-16 22:07 ` [PATCH v3 00/13] Add kdbus implementation Josh Boyer
2015-01-16 22:18   ` Greg Kroah-Hartman
2015-01-17  0:26     ` Daniel Mack
2015-01-17  0:41       ` Josh Boyer
2015-01-19 18:06 ` Johannes Stezenbach
2015-01-19 18:38   ` Greg Kroah-Hartman
2015-01-19 20:19     ` Johannes Stezenbach
2015-01-19 20:31       ` Greg Kroah-Hartman
2015-01-19 23:38         ` Johannes Stezenbach
2015-01-20  1:13           ` Greg Kroah-Hartman
2015-01-20 10:57             ` Johannes Stezenbach
2015-01-20 11:26               ` Greg Kroah-Hartman
2015-01-20 13:24                 ` Johannes Stezenbach
2015-01-20 14:12                   ` Michael Kerrisk (man-pages)
2015-01-26 21:32             ` One Thousand Gnomes
2015-01-19 18:33 ` Johannes Stezenbach
2015-01-20 14:05 ` Michael Kerrisk (man-pages)
2015-01-20 14:15 ` Michael Kerrisk (man-pages)

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