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From: Jason Gunthorpe <jgg@ziepe.ca>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Darren Hart <dvhart@infradead.org>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Linux FS-devel Mailing List <linux-fsdevel@vger.kernel.org>,
	gregkh <gregkh@linuxfoundation.org>,
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Subject: Re: [PATCH v2 05/17] compat_ioctl: move more drivers to generic_compat_ioctl_ptrarg
Date: Mon, 24 Sep 2018 14:35:05 -0600	[thread overview]
Message-ID: <20180924203505.GC6008@ziepe.ca> (raw)
In-Reply-To: <CAK8P3a17GY89in7PeLk1F2T-0Xq=sCrwwntM+Y4BCpXheUC+qQ@mail.gmail.com>

On Mon, Sep 24, 2018 at 10:18:52PM +0200, Arnd Bergmann wrote:
> On Tue, Sep 18, 2018 at 7:59 PM Jason Gunthorpe <jgg@ziepe.ca> wrote:
> >
> > On Tue, Sep 18, 2018 at 10:51:08AM -0700, Darren Hart wrote:
> > > On Fri, Sep 14, 2018 at 09:57:48PM +0100, Al Viro wrote:
> > > > On Fri, Sep 14, 2018 at 01:35:06PM -0700, Darren Hart wrote:
> > > >
> > > > > Acked-by: Darren Hart (VMware) <dvhart@infradead.org>
> > > > >
> > > > > As for a longer term solution, would it be possible to init fops in such
> > > > > a way that the compat_ioctl call defaults to generic_compat_ioctl_ptrarg
> > > > > so we don't have to duplicate this boilerplate for every ioctl fops
> > > > > structure?
> > > >
> > > >     Bad idea, that...  Because several years down the road somebody will add
> > > > an ioctl that takes an unsigned int for argument.  Without so much as looking
> > > > at your magical mystery macro being used to initialize file_operations.
> > >
> > > Fair, being explicit in the declaration as it is currently may be
> > > preferable then.
> >
> > It would be much cleaner and safer if you could arrange things to add
> > something like this to struct file_operations:
> >
> >   long (*ptr_ioctl) (struct file *, unsigned int, void __user *);
> >
> > Where the core code automatically converts the unsigned long to the
> > void __user * as appropriate.
> >
> > Then it just works right always and the compiler will help address
> > Al's concern down the road.
> 
> I think if we wanted to do this with a new file operation, the best
> way would be to do the copy_from_user()/copy_to_user() in the caller
> as well.
>
> We already do this inside of some subsystems, notably drivers/media/,
> and it simplifies the implementation of the ioctl handler function
> significantly. We obviously cannot do this in general, both because of
> traditional drivers that have 16-bit command codes (drivers/tty and others)
> and also because of drivers that by accident defined the commands
> incorrectly and use the wrong type or the wrong direction in the
> definition.

That could work well, but the first idea could be done globally and
mechanically, while this would require very careful per-driver
investigation. 

Particularly if the core code has worse performance.. ie due to
kmalloc calls or something.

I think it would make more sense to start by having the core do the
case to __user and then add another entry point to have the core do
the copy_from_user, and so on.

Jason

  reply	other threads:[~2018-09-24 20:35 UTC|newest]

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-09-12 15:01 [PATCH v2 01/17] compat_ioctl: add generic_compat_ioctl_ptrarg() Arnd Bergmann
2018-09-12 15:01 ` [PATCH v2 02/17] compat_ioctl: move drivers to generic_compat_ioctl_ptrarg Arnd Bergmann
2018-09-12 15:33   ` Jason Gunthorpe
2018-09-12 16:20     ` Arnd Bergmann
2018-09-12 18:13   ` Greg Kroah-Hartman
2018-09-16 19:07   ` Jarkko Sakkinen
2018-09-12 15:01 ` [PATCH v2 03/17] compat_ioctl: use correct compat_ptr() translation in drivers Arnd Bergmann
2018-09-12 18:13   ` Greg Kroah-Hartman
2018-09-13  0:48   ` Andrew Donnellan
2018-09-13 11:03   ` Felipe Balbi
2018-09-12 15:01 ` [PATCH v2 04/17] ceph: fix compat_ioctl for ceph_dir_operations Arnd Bergmann
2018-09-12 16:12   ` David Laight
2018-09-12 16:25     ` Arnd Bergmann
2018-09-13  0:48   ` Yan, Zheng
2018-09-12 15:08 ` [PATCH v2 05/17] compat_ioctl: move more drivers to generic_compat_ioctl_ptrarg Arnd Bergmann
2018-09-12 15:08   ` [PATCH v2 06/17] compat_ioctl: move rtc handling into rtc-dev.c Arnd Bergmann
2018-09-12 20:00     ` Alexandre Belloni
2018-09-12 15:08   ` [PATCH v2 07/17] compat_ioctl: move tape handling into drivers Arnd Bergmann
2018-09-12 15:08   ` [PATCH v2 08/17] compat_ioctl: remove keyboard ioctl translation Arnd Bergmann
2018-09-12 15:08   ` [PATCH v2 09/17] compat_ioctl: remove HIDIO translation Arnd Bergmann
2018-09-12 15:56   ` [PATCH v2 05/17] compat_ioctl: move more drivers to generic_compat_ioctl_ptrarg Jason Gunthorpe
2018-09-12 15:58   ` Daniel Vetter
2018-09-12 16:01   ` Mauro Carvalho Chehab
2018-09-12 18:13   ` Greg Kroah-Hartman
2018-09-14 14:23   ` David Sterba
2018-09-14 20:35   ` Darren Hart
2018-09-14 20:57     ` Al Viro
2018-09-18 17:51       ` Darren Hart
2018-09-18 17:59         ` Jason Gunthorpe
2018-09-24 20:18           ` Arnd Bergmann
2018-09-24 20:35             ` Jason Gunthorpe [this message]
2018-09-24 21:17               ` Arnd Bergmann
2018-09-17  9:33   ` Jonathan Cameron
2018-10-06  7:05   ` Bjorn Andersson
2018-09-12 15:13 ` [PATCH v2 10/17] compat_ioctl: remove translation for sound ioctls Arnd Bergmann
2018-09-12 15:13   ` [PATCH v2 11/17] compat_ioctl: remove isdn ioctl translation Arnd Bergmann
2018-09-12 15:13   ` [PATCH v2 12/17] compat_ioctl: remove IGNORE_IOCTL() Arnd Bergmann
2018-09-12 15:13   ` [PATCH v2 13/17] compat_ioctl: remove /dev/random commands Arnd Bergmann
2018-09-12 18:13     ` Greg Kroah-Hartman
2018-09-12 15:13   ` [PATCH v2 14/17] compat_ioctl: remove joystick ioctl translation Arnd Bergmann
2018-09-12 15:13   ` [PATCH v2 15/17] compat_ioctl: remove PCI " Arnd Bergmann
2018-09-12 15:13   ` [PATCH v2 16/17] compat_ioctl: remove /dev/raw " Arnd Bergmann
2018-09-12 15:13   ` [PATCH v2 17/17] compat_ioctl: remove last RAID handling code Arnd Bergmann
2018-09-13 13:37   ` [PATCH v2 10/17] compat_ioctl: remove translation for sound ioctls Takashi Iwai
2018-09-13  2:07 ` [PATCH v2 01/17] compat_ioctl: add generic_compat_ioctl_ptrarg() Al Viro
2018-09-13 10:29   ` Arnd Bergmann
2018-10-28 17:07     ` Al Viro
2018-10-29  9:50       ` Arnd Bergmann

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