From: Chen Guanqiao <chen.chenchacha@foxmail.com>
To: hirofumi@mail.parknet.co.jp
Cc: linux-kernel@vger.kernel.org,
        Chen Guanqiao <chen.chenchacha@foxmail.com>
Subject: [PATCH] fs: fat: add ioctl to modify fat filesystem volume label
Date: Wed, 20 Dec 2017 22:05:47 +0800
Message-Id: <20171220140547.5173-1-chen.chenchacha@foxmail.com>
Feedback-ID: esmtp:foxmail.com:bgforeign:bgforeign3
Sender: linux-kernel-owner@vger.kernel.org
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The FAT filesystem volume label can be read with FAT_IOCTL_GET_VOLUME_LABEL
and written with FAT_IOCTL_SET_VOLUME_LABEL.

Signed-off-by: Chen Guanqiao <chen.chenchacha@foxmail.com>
---
 fs/fat/fat.h                  |  1 +
 fs/fat/file.c                 | 51 +++++++++++++++++++++++++++++++++++++++++++
 fs/fat/inode.c                | 15 ++++++++++---
 include/uapi/linux/msdos_fs.h |  2 ++
 4 files changed, 66 insertions(+), 3 deletions(-)

diff --git a/fs/fat/fat.h b/fs/fat/fat.h
index 8fc1093da47d..204012c94421 100644
--- a/fs/fat/fat.h
+++ b/fs/fat/fat.h
@@ -86,6 +86,7 @@ struct msdos_sb_info {
	int dir_per_block;	      /* dir entries per block */
	int dir_per_block_bits;	      /* log2(dir_per_block) */
	unsigned int vol_id;		/*volume ID*/
+	char vol_label[11];		/*volume label*/

	int fatent_shift;
	const struct fatent_operations *fatent_ops;
diff --git a/fs/fat/file.c b/fs/fat/file.c
index 4724cc9ad650..5d2990c44705 100644
--- a/fs/fat/file.c
+++ b/fs/fat/file.c
@@ -121,6 +121,53 @@ 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,
+									  u32 __user *user_attr)
+{
+	struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
+	u8 __user *vol_label = (u8 __user *)user_attr;
+
+	return copy_to_user(vol_label, sbi->vol_label, sizeof(sbi->vol_label));
+}
+
+static int fat_ioctl_set_volume_label(struct inode *inode,
+									  u32 __user *user_attr)
+{
+	struct buffer_head *bh;
+	struct fat_boot_sector *b;
+	struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
+	u8 __user *vol_label = (u8 __user *)user_attr;
+	u8 label[11];
+
+	if (copy_from_user(label, vol_label, sizeof(label)))
+		return -EFAULT;
+
+	if (sb_rdonly(inode->i_sb))
+		return -EFAULT;
+
+	bh = sb_bread(inode->i_sb, 0);
+	if (bh == NULL) {
+		fat_msg(inode->i_sb, KERN_ERR,
+				"unable to read boot sector to write volume label");
+		return -EFAULT;
+	}
+
+	b = (struct fat_boot_sector *) bh->b_data;
+
+	if (sbi->fat_bits == 32)
+		memcpy(b->fat32.vol_label, label, sizeof(label));
+	else
+		memcpy(b->fat16.vol_label, label, sizeof(label));
+
+	mark_buffer_dirty(bh);
+	sync_dirty_buffer(bh);
+	brelse(bh);
+
+	memcpy(sbi->vol_label, label, sizeof(sbi->vol_label));
+
+	return 0;
+}
+
 long fat_generic_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 {
	struct inode *inode = file_inode(filp);
@@ -133,6 +180,10 @@ 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_attr);
+	case FAT_IOCTL_SET_VOLUME_LABEL:
+		return fat_ioctl_set_volume_label(inode, user_attr);
	default:
		return -ENOTTY;	/* Inappropriate ioctl for device */
	}
diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index 20a0a89eaca5..9991500c98af 100644
--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -45,12 +45,14 @@ struct fat_bios_param_block {

	u8	fat16_state;
	u32	fat16_vol_id;
+	u8  fat16_vol_label[11];

	u32	fat32_length;
	u32	fat32_root_cluster;
	u16	fat32_info_sector;
	u8	fat32_state;
	u32	fat32_vol_id;
+	u8  fat32_vol_label[11];
 };

 static int fat_default_codepage = CONFIG_FAT_DEFAULT_CODEPAGE;
@@ -1460,12 +1462,16 @@ static int fat_read_bpb(struct super_block *sb, struct fat_boot_sector *b,

	bpb->fat16_state = b->fat16.state;
	bpb->fat16_vol_id = get_unaligned_le32(b->fat16.vol_id);
+	memcpy(bpb->fat16_vol_label, b->fat16.vol_label,
+		   sizeof(bpb->fat16_vol_label));

	bpb->fat32_length = le32_to_cpu(b->fat32.length);
	bpb->fat32_root_cluster = le32_to_cpu(b->fat32.root_cluster);
	bpb->fat32_info_sector = le16_to_cpu(b->fat32.info_sector);
	bpb->fat32_state = b->fat32.state;
	bpb->fat32_vol_id = get_unaligned_le32(b->fat32.vol_id);
+	memcpy(bpb->fat32_vol_label, b->fat32.vol_label,
+		   sizeof(bpb->fat32_vol_label));

	/* Validate this looks like a FAT filesystem BPB */
	if (!bpb->fat_reserved) {
@@ -1723,11 +1729,14 @@ 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)
+	/* interpret volume ID and label as a little endian 32 bit integer */
+	if (sbi->fat_bits == 32) {
		sbi->vol_id = bpb.fat32_vol_id;
-	else /* fat 16 or 12 */
+		memcpy(sbi->vol_label, bpb.fat32_vol_label, sizeof(sbi->vol_label));
+	} else { /* fat 16 or 12 */
		sbi->vol_id = bpb.fat16_vol_id;
+		memcpy(sbi->vol_label, bpb.fat16_vol_label, sizeof(sbi->vol_label));
+	}

	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 a45d0754102e..799f9a6cb99d 100644
--- a/include/uapi/linux/msdos_fs.h
+++ b/include/uapi/linux/msdos_fs.h
@@ -107,6 +107,8 @@ 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[11])
+#define FAT_IOCTL_SET_VOLUME_LABEL	_IOR('r', 0x15, __u8[11])

 struct fat_boot_sector {
	__u8	ignored[3];	/* Boot strap short or near jump */
--
2.15.1