From: Ian Abbott <abbotti@mev.co.uk>
To: David Laight <David.Laight@ACULAB.COM>,
Greg KH <gregkh@linuxfoundation.org>,
Atul Gopinathan <atulgopinathan@gmail.com>
Cc: "devel@driverdev.osuosl.org" <devel@driverdev.osuosl.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] staging: comedi: cast to (unsigned int *)
Date: Fri, 19 Feb 2021 09:31:16 +0000 [thread overview]
Message-ID: <94917044-ba8f-7044-42f6-7e8d5ef1e10b@mev.co.uk> (raw)
In-Reply-To: <21a953261eb44e7ba302cfe74d8efa2d@AcuMS.aculab.com>
On 19/02/2021 09:03, David Laight wrote:
>> It's kind of moot anyway because the patch is outdated. But the reason
>> for the ___force is that the same `struct comedi_cmd` is used in both
>> user and kernel contexts. In user contexts, the `chanlist` member
>> points to user memory and in kernel contexts it points to kernel memory
>> (copied from userspace).
>
> Can't you use a union of the user and kernel pointers?
> (Possibly even anonymous?)
> Although, ideally, keeping them in separate fields is better.
> 8 bytes for a pointer isn't going make a fat lot of difference.
This is for a UAPI header (eventually), so cannot add a new field. For
an anonymous union, one tagged with __user and one not, the __user tag
would be removed during conversion from UAPI headers to
/usr/include/linux headers, leaving a union of two identically typed
members, which would look a bit odd. The union also kind of hides the
problem.
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prev parent reply other threads:[~2021-02-19 9:31 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-17 16:59 [PATCH] staging: comedi: cast to (unsigned int *) Atul Gopinathan
2021-02-17 17:35 ` Greg KH
2021-02-17 18:10 ` Atul Gopinathan
2021-02-17 18:26 ` Greg KH
2021-02-18 11:04 ` Ian Abbott
2021-02-19 9:03 ` David Laight
2021-02-19 9:26 ` Dan Carpenter
2021-02-19 9:36 ` David Laight
2021-02-19 9:31 ` Ian Abbott [this message]
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