linux-kernel - Re: [PATCH V3] mmc: block: Add new ioctl to send multi commands

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Date:	Mon, 21 Sep 2015 11:40:32 -0700
From:	Grant Grundler <grundler@...gle.com>
To:	Jon Hunter <jonathanh@...dia.com>
Cc:	Gwendal Grignou <gwendal@...omium.org>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Seshagiri Holi <sholi@...dia.com>,
	Arnd Bergmann <arnd@...db.de>,
	Olof Johansson <olofj@...omium.org>
Subject: Re: [PATCH V3] mmc: block: Add new ioctl to send multi commands

Jon, Ulf,
Can we first get the current implementation upstream and _then_ add
more patches to it?

On Mon, Sep 21, 2015 at 4:19 AM, Jon Hunter <jonathanh@...dia.com> wrote:
...
>>>> +       for (i = 0; i < num_of_cmds; i++) {
>>>> +               err = __mmc_blk_ioctl_cmd(card, md, idata[i]);
>>>> +               if (err) {
>>>> +                       mmc_put_card(card);
>>>> +                       goto cmd_done;
>>> Instead of exiting here, you should first copy to the user the data
>>> and response of successful commands, mark the failed command as failed
>>> and the remaining ones as "not executed".
>>> This way, it will be easier for the user space application to find out
>>> where the sequence failed. This especially true if some reverts are
>>> needed.
>>
>> Yes that sounds like a sensible thing to do. I will incorporate that change.

I also liked Gwendal's idea and incorporated that into our 3.18 kernel
tree here:
    https://chromium-review.googlesource.com/#/c/299956

(this is on top of Jon's most recently proposed patch - we'll align
with what lands shortly)

But as I've demonstrated, this can be a separate patch.

cheers,
grant

>
> At first, I thought that may be the response field of the command could
> be used to indicate the failed command. However, thinking about this
> some more, I am not sure that it seems correct to use this field as this
> is really used to carry the MMC response as defined by the MMC
> specification.
>
> Should the response field always be non-zero for a successful command?
> If this is guaranteed, then may be the best thing to do would be to have
> user-space clear the response field to field before submitting the
> commands. It would then be easy to detect which command failed and which
> were not attempted.
>
> Ulf, what are your thoughts?
>
> Cheers
> Jon
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