Re: [PATCH RFC] Add FAT_IOCTL_GET_VOLUME_ID

[OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>]

bintian.wang@linaro.org writes:

> From: Mike Lockwood <lockwood@android.com>
>
> This patch, originally from Android kernel, 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 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.
>
> Android uses vfat volume ID to identify different sd card, when a new sd card
> is inserted to device, android can scan the media on it and pop up new contents.

Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>

Thanks.

> Cc: dmitry pervushin <dpervushin@gmail.com>
> Cc: Mike Lockwood <lockwood@android.com>
> Cc: Colin Cross <ccross@android.com>
> Cc: Android Kernel Team <kernel-team@android.com>
> Cc: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: John Stultz <john.stultz@linaro.org>
> Cc: Sean McNeil <sean@mcneil.com>
>
> Signed-off-by: Bintian Wang <bintian.wang@linaro.org>
> ---
>  fs/fat/fat.h                  |    1 +
>  fs/fat/file.c                 |    8 ++++++++
>  fs/fat/inode.c                |   12 ++++++++++++
>  include/uapi/linux/msdos_fs.h |   10 ++++++++++
>  4 files changed, 31 insertions(+)
>
> diff --git a/fs/fat/fat.h b/fs/fat/fat.h
> index 21664fc..4241e6f 100644
> --- a/fs/fat/fat.h
> +++ b/fs/fat/fat.h
> @@ -86,6 +86,7 @@ struct msdos_sb_info {
>  	const void *dir_ops;	      /* Opaque; default directory operations */
>  	int dir_per_block;	      /* dir entries per block */
>  	int dir_per_block_bits;	      /* log2(dir_per_block) */
> +	unsigned int vol_id;		/*volume ID*/
>  
>  	int fatent_shift;
>  	struct fatent_operations *fatent_ops;
> diff --git a/fs/fat/file.c b/fs/fat/file.c
> index b0b632e..9b104f5 100644
> --- a/fs/fat/file.c
> +++ b/fs/fat/file.c
> @@ -114,6 +114,12 @@ out:
>  	return err;
>  }
>  
> +static int fat_ioctl_get_volume_id(struct inode *inode, u32 __user *user_attr)
> +{
> +	struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
> +	return put_user(sbi->vol_id, user_attr);
> +}
> +
>  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 fat_ioctl_get_volume_id(inode, user_attr);
>  	default:
>  		return -ENOTTY;	/* Inappropriate ioctl for device */
>  	}
> diff --git a/fs/fat/inode.c b/fs/fat/inode.c
> index 5d4513c..11b51bb 100644
> --- a/fs/fat/inode.c
> +++ b/fs/fat/inode.c
> @@ -1415,6 +1415,18 @@ int fat_fill_super(struct super_block *sb, void *data, int silent, int isvfat,
>  		brelse(fsinfo_bh);
>  	}
>  
> +	/* interpret volume ID as a little endian 32 bit integer */
> +	if (sbi->fat_bits == 32)
> +		sbi->vol_id = (((u32)b->fat32.vol_id[0]) |
> +					((u32)b->fat32.vol_id[1] << 8) |
> +					((u32)b->fat32.vol_id[2] << 16) |
> +					((u32)b->fat32.vol_id[3] << 24));
> +	else /* fat 16 or 12 */
> +		sbi->vol_id = (((u32)b->fat16.vol_id[0]) |
> +					((u32)b->fat16.vol_id[1] << 8) |
> +					((u32)b->fat16.vol_id[2] << 16) |
> +					((u32)b->fat16.vol_id[3] << 24));
> +
>  	sbi->dir_per_block = sb->s_blocksize / sizeof(struct msdos_dir_entry);
>  	sbi->dir_per_block_bits = ffs(sbi->dir_per_block) - 1;
>  
> diff --git a/include/uapi/linux/msdos_fs.h b/include/uapi/linux/msdos_fs.h
> index f055e58..e284ff9 100644
> --- a/include/uapi/linux/msdos_fs.h
> +++ b/include/uapi/linux/msdos_fs.h
> @@ -104,6 +104,8 @@ struct __fat_dirent {
>  /* <linux/videotext.h> has used 0x72 ('r') in collision, so skip a few */
>  #define FAT_IOCTL_GET_ATTRIBUTES	_IOR('r', 0x10, __u32)
>  #define FAT_IOCTL_SET_ATTRIBUTES	_IOW('r', 0x11, __u32)
> +/*Android kernel has used 0x12, so we use 0x13*/
> +#define FAT_IOCTL_GET_VOLUME_ID		_IOR('r', 0x13, __u32)
>  
>  struct fat_boot_sector {
>  	__u8	ignored[3];	/* Boot strap short or near jump */
> @@ -128,6 +130,10 @@ struct fat_boot_sector {
>  			__u8	drive_number;	/* Physical drive number */
>  			__u8	state;		/* undocumented, but used
>  						   for mount state. */
> +			__u8	signature;  /* extended boot signature */
> +			__u8	vol_id[4];	/* volume ID */
> +			__u8	vol_label[11];	/* volume label */
> +			__u8	fs_type[8];		/* file system type */
>  			/* other fiealds are not added here */
>  		} fat16;
>  
> @@ -147,6 +153,10 @@ struct fat_boot_sector {
>  			__u8	drive_number;   /* Physical drive number */
>  			__u8    state;       	/* undocumented, but used
>  						   for mount state. */
> +			__u8	signature;  /* extended boot signature */
> +			__u8	vol_id[4];	/* volume ID */
> +			__u8	vol_label[11];	/* volume label */
> +			__u8	fs_type[8];		/* file system type */
>  			/* other fiealds are not added here */
>  		} fat32;
>  	};

-- 
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>