linux-kernel - Re: [PATCH RFC] Add FAT_IOCTL_GET_VOLUME

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Date:	Mon, 01 Jul 2013 21:00:54 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	bintian.wang@...aro.org
Cc:	linux-kernel@...r.kernel.org, Mike Lockwood <lockwood@...roid.com>,
	dmitry pervushin <dpervushin@...il.com>,
	Colin Cross <ccross@...roid.com>,
	Android Kernel Team <kernel-team@...roid.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	John Stultz <john.stultz@...aro.org>
Subject: Re: [PATCH RFC] Add FAT_IOCTL_GET_VOLUME_ID

bintian.wang@...aro.org writes:

> From: Mike Lockwood <lockwood@...roid.com>
>
> Adds vfat ioctl command FAT_IOCTL_GET_VOLUME_ID, with this command 
> we can get the vfat volume ID using following code:
>
> 	ioctl(fd, FAT_IOCTL_GET_VOLUME_ID, &volume_ID)
>
> This patch is a modified version of the android kernel patch by Mike Lockwood, 
> the original patch makes the return value of ioctl() as the volume ID, 
> Dmitry Pervushin noticed some volume IDs abiguous with error returns:
> for example, if volume id is set to "0xFFFFFDAD", that matches -ENOIOCTLCMD, 
> we get a wrong volume ID "0xFFFFFFFF" from the user space.
>
> This patch fixes above bug by adding a parameter to ioctl to get the correct
> volume ID.

Personally, I have no objection to do this small one in kernel
though. Please add use case of android to changelog, it would help to
understand.

> +static unsigned int fat_ioctl_volume_id(struct inode *inode)
> +{
> +	struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
> +	return sbi->vol_id;
> +}
> +
>  long fat_generic_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
>  {
>  	struct inode *inode = file_inode(filp);
> @@ -124,6 +130,8 @@ long fat_generic_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
>  		return fat_ioctl_get_attributes(inode, user_attr);
>  	case FAT_IOCTL_SET_ATTRIBUTES:
>  		return fat_ioctl_set_attributes(filp, user_attr);
> +	case FAT_IOCTL_GET_VOLUME_ID:
> +		return put_user(fat_ioctl_volume_id(inode), user_attr);
>  	default:
>  		return -ENOTTY;	/* Inappropriate ioctl for device */
>  	}

Please push put_user() down into fat_ioctl_volume_id() like others. So,
generic_ioctl() itself can forget about the detail of each ioctl.

Thanks.
-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
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