linux-kernel - Re: Questions about mmap

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Message-ID: <48E8C8AB.3010308@s5r6.in-berlin.de>
Date:	Sun, 05 Oct 2008 16:01:15 +0200
From:	Stefan Richter <stefanr@...6.in-berlin.de>
To:	Thiago Lacerda <thiagotbl@...il.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: Questions about mmap

Thiago Lacerda wrote:
> typedef struct hashtable {
>    flow_t *hashBuckets[X]; // X is a natural number
>    unsigned int size;
> } Hastable;
> 
> 
> So, my question is: Can I mmap the hashtable struct and access
> directly from userspace? I'm afraid that this could turn on mess
> because of the array of pointers.
> If it's possible, does anyone know a piece of code that can match my
> problem? I've been googling and I just find codes dealing with structs
> itself, not pointers.

If you require portability, you can only use integer types of fixed size
in kernel<->userspace ABIs.  Pointers can then be exchanged as __u64
under the assumption that pointers not wider than 64 bits.  See for
example the FW_CDEV_IOC_QUEUE_ISO ioctl in include/linux/firewire-cdev.h.
-- 
Stefan Richter
-=====-==--- =-=- --=-=
http://arcgraph.de/sr/
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