linux-kernel - Re: [RFC PATCH] mmc: block: Add new ioctl to send combo commands

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Date:	Thu, 3 Sep 2015 16:10:18 +0100
From:	Jon Hunter <jonathanh@...dia.com>
To:	Grant Grundler <grundler@...gle.com>,
	Olof Johansson <olof@...om.net>
CC:	Ulf Hansson <ulf.hansson@...aro.org>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Olof Johansson <olofj@...omium.org>,
	Seshagiri Holi <sholi@...dia.com>
Subject: Re: [RFC PATCH] mmc: block: Add new ioctl to send combo commands


On 02/09/15 23:08, Grant Grundler wrote:
> [resending text-only]
> 
> On Wed, Sep 2, 2015 at 3:07 PM, Grant Grundler <grundler@...gle.com> wrote:
>>
>>
>> On Wed, Sep 2, 2015 at 11:28 AM, Olof Johansson <olof@...om.net> wrote:
>> ...
>>>> +/**
>>>> + * struct mmc_ioc_combo_cmd - combo command information
>>>> + * @num_of_cmds: number of commands to send
>>>> + * @mmc_ioc_cmd_list: pointer to list of commands
>>>> + */
>>>> +struct mmc_ioc_combo_cmd {
>>>> +       uint8_t num_of_cmds;
>>>> +       struct mmc_ioc_cmd *mmc_ioc_cmd_list;
>>>> +};
>>>
>>> The size of this struct will depend on the pointer size of userspace.
>>>
>>> It might be better to use a u64 for the pointer instead. Otherwise
>>> you'd need a compat ioctl wrapper to copy a 32-bit pointer over on a
>>> 64-bit kernel.
>>
>> If alignment matters, then maybe swap the fields?
>> Or declare num_of_cmds as u64 as well?

Thanks. I did swap them in the updated version as this seems to make
sense. However, I left num_of_cmds as an 8-bit value unless someone has
a need for more than 256 commands ;-)

Jon
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