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

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Date:	Mon, 01 Jul 2013 15:12:22 +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:

> This patch, originally from Android kernel, adds vfat directory ioctl command
> FAT_IOCTL_GET_VOLUME_ID, with this command we can get the vfat volume ID using
> following code:
>
> 	ioctl(dirfd(dir), FAT_IOCTL_GET_VOLUME_ID, &volume_ID)
>
> This patch is a modified version of the patch by Mike Lockwood, with changes
> from Dmitry Pervushin, who noticed the original patch makes some volume IDs
> abiguous with error returns: for example, if volume id is 0xFFFFFDAD, that
> matches -ENOIOCTLCMD, we get "FFFFFFFF" from the user space.
>
> So add a parameter to ioctl to get the correct volume ID.

Adding more specific usage example to changelog would help for
understanding this.

> +	case FAT_IOCTL_GET_VOLUME_ID:
> +		id = fat_ioctl_volume_id(inode);
> +		return copy_to_user((unsigned int *)arg, &id, sizeof(id));

> +	case FAT_IOCTL_GET_VOLUME_ID:
> +		id = fat_ioctl_volume_id(inode);
> +		return copy_to_user((unsigned int *)arg, &id, sizeof(id));

This pattern seems to from put_user().

Unnecessary cast of 1st arg. And copy_to_user() returns remaining bytes
when fail (not error code).

> +struct fat_boot_bsx {
> +	__u8     drive;     /* drive number */
> +	__u8     reserved1;
> +	__u8     signature; /* extended boot signature */
> +	__u8     vol_id[4]; /* volume ID */
> +	__u8     vol_label[11]; /* volume label */
> +	__u8     type[8];   /* file system type */
> +};
> +#define FAT16_BSX_OFFSET 36 /* offset of fat_boot_bsx in FAT12 and FAT16 */
> +#define FAT32_BSX_OFFSET 64 /* offset of fat_boot_bsx in FAT32 */

There is any issue to merge those to "struct fat_boot_sector"? I guess,
merging it is cleaner way.

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