linux-kernel - Re: [PATCH 1/2] Add FAT_IOCTL_GET_VOLUME_LABEL in fat_generic

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Date:   Thu, 4 Oct 2018 19:33:47 +0200
From:   Pali Rohár <pali.rohar@...il.com>
To:     chenchacha <chen.chenchacha@...mail.com>
Cc:     hirofumi@...l.parknet.co.jp, linux-kernel@...r.kernel.org,
        andy.shevchenko@...il.com
Subject: Re: [PATCH 1/2] Add FAT_IOCTL_GET_VOLUME_LABEL in fat_generic_ioctl()

On Friday 05 October 2018 01:21:00 chenchacha wrote:
> Signed-off-by: chenchacha <chen.chenchacha@...mail.com>
> ---
>  fs/fat/file.c                 | 22 ++++++++++++++++++++++
>  include/uapi/linux/msdos_fs.h |  1 +
>  2 files changed, 23 insertions(+)
> 
> diff --git a/fs/fat/file.c b/fs/fat/file.c
> index 4724cc9ad650..56db0b5a8df1 100644
> --- a/fs/fat/file.c
> +++ b/fs/fat/file.c
> @@ -121,10 +121,30 @@ static int fat_ioctl_get_volume_id(struct inode *inode, u32 __user *user_attr)
>  	return put_user(sbi->vol_id, user_attr);
>  }
>  
> +static int fat_ioctl_get_volume_label(struct inode *inode, u8 __user *label)
> +{
> +	struct super_block *sb = inode->i_sb;
> +	struct inode *root_inode = d_inode(sb->s_root);
> +	struct buffer_head *bh = NULL;
> +	struct msdos_dir_entry *de;
> +	int err;
> +
> +	inode_lock_shared(root_inode);
> +	err = fat_get_root_entry(root_inode, &bh, &de);
> +	if (err == 0) {
> +		if (copy_to_user(label, de->name, MSDOS_NAME))

You need to convert entry name from 8.3 format to label in correct
encoding specified by codepage mount option. Plus needs to handle
leading 0x03 byte.

> +			err = -EFAULT;
> +	}
> +	inode_unlock_shared(root_inode);
> +
> +	return err;
> +}
> +
>  long fat_generic_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
>  {
>  	struct inode *inode = file_inode(filp);
>  	u32 __user *user_attr = (u32 __user *)arg;
> +	u8 __user *user_vol_label = (u8 __user *)arg;
>  
>  	switch (cmd) {
>  	case FAT_IOCTL_GET_ATTRIBUTES:
> @@ -133,6 +153,8 @@ long fat_generic_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
>  		return fat_ioctl_set_attributes(filp, user_attr);
>  	case FAT_IOCTL_GET_VOLUME_ID:
>  		return fat_ioctl_get_volume_id(inode, user_attr);
> +	case FAT_IOCTL_GET_VOLUME_LABEL:
> +		return fat_ioctl_get_volume_label(inode, user_vol_label);
>  	default:
>  		return -ENOTTY;	/* Inappropriate ioctl for device */
>  	}
> diff --git a/include/uapi/linux/msdos_fs.h b/include/uapi/linux/msdos_fs.h
> index fde753735aba..8ba8e2d7bafe 100644
> --- a/include/uapi/linux/msdos_fs.h
> +++ b/include/uapi/linux/msdos_fs.h
> @@ -109,6 +109,7 @@ struct __fat_dirent {
>  #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)
> +#define FAT_IOCTL_GET_VOLUME_LABEL	_IOR('r', 0x14, __u8[MSDOS_NAME])
>  
>  struct fat_boot_sector {
>  	__u8	ignored[3];	/* Boot strap short or near jump */

-- 
Pali Rohár
pali.rohar@...il.com

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