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

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Date:	Thu, 10 Sep 2015 09:43:42 +0100
From:	Jon Hunter <jonathanh@...dia.com>
To:	Ulf Hansson <ulf.hansson@...aro.org>
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

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.

Cheers
Jon
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