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

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Date:	Thu, 10 Sep 2015 12:13:15 +0200
From:	Ulf Hansson <ulf.hansson@...aro.org>
To:	Jon Hunter <jonathanh@...dia.com>
Cc:	Olof Johansson <olof@...om.net>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Grant Grundler <grundler@...gle.com>,
	Olof Johansson <olofj@...omium.org>,
	Seshagiri Holi <sholi@...dia.com>
Subject: Re: [RFC PATCH] mmc: block: Add new ioctl to send combo commands

On 10 September 2015 at 10:43, Jon Hunter <jonathanh@...dia.com> wrote:
> Hi Ulf,
>
> On 09/09/15 13:42, Ulf Hansson wrote:
>
> [snip]
>
>>> +static int mmc_blk_ioctl_cmd(struct block_device *bdev,
>>> +                       struct mmc_ioc_cmd __user *ic_ptr)
>>> +{
>>> +       struct mmc_blk_ioc_data *idata;
>>> +       struct mmc_blk_data *md;
>>> +       struct mmc_card *card;
>>> +       int err;
>>> +
>>> +       /*
>>> +        * The caller must have CAP_SYS_RAWIO, and must be calling this on the
>>> +        * whole block device, not on a partition.  This prevents overspray
>>> +        * between sibling partitions.
>>> +        */
>>> +       if ((!capable(CAP_SYS_RAWIO)) || (bdev != bdev->bd_contains))
>>> +               return -EPERM;
>>> +
>>> +       idata = mmc_blk_ioctl_copy_from_user(ic_ptr);
>>> +       if (IS_ERR(idata))
>>> +               return PTR_ERR(idata);
>>> +
>>> +       md = mmc_blk_get(bdev->bd_disk);
>>> +       if (!md) {
>>> +               err = -EINVAL;
>>> +               goto cmd_err;
>>> +       }
>>> +
>>> +       card = md->queue.card;
>>> +       if (IS_ERR(card)) {
>>> +               err = PTR_ERR(card);
>>> +               goto cmd_done;
>>> +       }
>>> +
>>> +       mmc_claim_host(card->host);
>>
>> As __mmc_blk_ioctl_cmd() already does mmc_get_card(), you don't need
>> mmc_claim_host() here.
>
> Thinking about this some more, does it make sense to have a
> mmc_get_card() above and then remove the one from __mmc_blk_ioctl_cmd()?
> The mmc_blk_ioctl_multi_cmd() needs to call mmc_get_card() before
> calling __mmc_blk_ioctl_cmd() and so currently we are calling
> mmc_get_card() twice in the case of mmc_blk_ioctl_multi_cmd() which
> seems unnecessary.

I agree.

We can follow your suggestion, but then we also need to add
mmc_get|put_card() in the case for non-multi commands.

Kind regards
Uffe
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