FAT: Add new ioctl VFAT_IOCTL_GET_VOLUME_ID for reading the volume ID.

Signed-off-by: Brian Swetland <swetland@google.com>

4 files changed, 31 insertions, 0 deletions

diff --git a/fs/fat/dir.c b/fs/fat/dir.c
index ee42b9e0b16a..2242ac239866 100644
--- a/fs/fat/dir.c
+++ b/fs/fat/dir.c
@@ -753,6 +753,13 @@ static int fat_ioctl_readdir(struct inode *inode, struct file *filp,
 	return ret;
 }
 
+static int fat_ioctl_volume_id(struct inode *dir)
+{
+	struct super_block *sb = dir->i_sb;
+	struct msdos_sb_info *sbi = MSDOS_SB(sb);
+	return sbi->vol_id;
+}
+
 static long fat_dir_ioctl(struct file *filp, unsigned int cmd,
 			  unsigned long arg)
 {
@@ -769,6 +776,8 @@ static long fat_dir_ioctl(struct file *filp, unsigned int cmd,
 		short_only = 0;
 		both = 1;
 		break;
+	case VFAT_IOCTL_GET_VOLUME_ID:
+		return fat_ioctl_volume_id(inode);
 	default:
 		return fat_generic_ioctl(filp, cmd, arg);
 	}
diff --git a/fs/fat/fat.h b/fs/fat/fat.h
index d75a77f85c28..91cfdda6fb7b 100644
--- a/fs/fat/fat.h
+++ b/fs/fat/fat.h
@@ -78,6 +78,7 @@ 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 long vol_id;        /* volume ID */
 
 	int fatent_shift;
 	struct fatent_operations *fatent_ops;
diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index 830058057d33..ab81a7e31157 100644
--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -1247,6 +1247,7 @@ int fat_fill_super(struct super_block *sb, void *data, int silent,
 	struct inode *root_inode = NULL, *fat_inode = NULL;
 	struct buffer_head *bh;
 	struct fat_boot_sector *b;
+	struct fat_boot_bsx *bsx;
 	struct msdos_sb_info *sbi;
 	u16 logical_sector_size;
 	u32 total_sectors, total_clusters, fat_clusters, rootdir_sectors;
@@ -1391,6 +1392,8 @@ int fat_fill_super(struct super_block *sb, void *data, int silent,
 			goto out_fail;
 		}
 
+		bsx = (struct fat_boot_bsx *)(bh->b_data + FAT32_BSX_OFFSET);
+
 		fsinfo = (struct fat_boot_fsinfo *)fsinfo_bh->b_data;
 		if (!IS_FSINFO(fsinfo)) {
 			printk(KERN_WARNING "FAT: Invalid FSINFO signature: "
@@ -1406,8 +1409,14 @@ int fat_fill_super(struct super_block *sb, void *data, int silent,
 		}
 
 		brelse(fsinfo_bh);
+	} else {
+		bsx = (struct fat_boot_bsx *)(bh->b_data + FAT16_BSX_OFFSET);
 	}
 
+	/* interpret volume ID as a little endian 32 bit integer */
+	sbi->vol_id = (((u32)bsx->vol_id[0]) | ((u32)bsx->vol_id[1] << 8) |
+		((u32)bsx->vol_id[2] << 16) | ((u32)bsx->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/linux/msdos_fs.h b/include/linux/msdos_fs.h
index 34066e65fdeb..f38d4f0a5ae8 100644
--- a/include/linux/msdos_fs.h
+++ b/include/linux/msdos_fs.h
@@ -101,6 +101,7 @@ 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)
+#define VFAT_IOCTL_GET_VOLUME_ID	_IOR('r', 0x12, __u32)
 
 struct fat_boot_sector {
 	__u8	ignored[3];	/* Boot strap short or near jump */
@@ -138,6 +139,17 @@ struct fat_boot_fsinfo {
 	__le32   reserved2[4];
 };
 
+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 */
+
 struct msdos_dir_entry {
 	__u8	name[MSDOS_NAME];/* name and extension */
 	__u8	attr;		/* attribute bits */