linux-kernel - Re: Why is the 'loff_t *offset' parameter in the file

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Message-Id: <201104261437.53925.arnd@arndb.de>
Date:	Tue, 26 Apr 2011 14:37:53 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Amit Ben Shahar <amit.bens@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Why is the 'loff_t *offset' parameter in the file_operations' read function a pointer?

On Tuesday 26 April 2011, Amit Ben Shahar wrote:
> (if i'm off topic or should look elsewhere i apologize - couldn't find
> information anywhere)
> I am coding a kernel module and implementing a file's operations, the
> read operation received an loff_t *offset parameter, why is this a
> pointer? is it in userspace?

The read function must update the offset independent of the return value.
See simple_read_from_buffer() as an example.

	Arnd
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