hfsplus: add an ioctl to bless files

Making an hfsplus partition bootable requires the ability to "bless" a
file by putting its inode number in the volume header. Doing this from
userspace on a mounted filesystem is impractical since the kernel will
write back the original values on unmount. Add an ioctl to allow userspace
to update the volume header information based on the target file.
Signed-off-by: Matthew Garrett <mjg@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Documentation/ioctl/ioctl-number.txt

@@ -218,6 +218,7 @@ Code  Seq#(hex)	Include File		Comments
 'h'	00-7F				conflict! Charon filesystem
 					<mailto:zapman@interlan.net>
 'h'	00-1F	linux/hpet.h		conflict!
+'h'	80-8F	fs/hfsplus/ioctl.c
 'i'	00-3F	linux/i2o-dev.h		conflict!
 'i'	0B-1F	linux/ipmi.h		conflict!
 'i'	80-8F	linux/i8k.h

fs/hfsplus/hfsplus_fs.h

@@ -316,6 +316,11 @@ static inline unsigned short hfsplus_min_io_size(struct super_block *sb)
 #define HFSPLUS_IOC_EXT2_SETFLAGS	FS_IOC_SETFLAGS
 
 
+/*
+ * hfs+-specific ioctl for making the filesystem bootable
+ */
+#define HFSPLUS_IOC_BLESS _IO('h', 0x80)
+
 /*
  * Functions in any *.c used in other files
  */

fs/hfsplus/ioctl.c

@@ -20,6 +20,38 @@
 #include <asm/uaccess.h>
 #include "hfsplus_fs.h"
 
+/*
+ * "Blessing" an HFS+ filesystem writes metadata to the superblock informing
+ * the platform firmware which file to boot from
+ */
+static int hfsplus_ioctl_bless(struct file *file, int __user *user_flags)
+{
+	struct dentry *dentry = file->f_path.dentry;
+	struct inode *inode = dentry->d_inode;
+	struct hfsplus_sb_info *sbi = HFSPLUS_SB(inode->i_sb);
+	struct hfsplus_vh *vh = sbi->s_vhdr;
+	struct hfsplus_vh *bvh = sbi->s_backup_vhdr;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	mutex_lock(&sbi->vh_mutex);
+
+	/* Directory containing the bootable system */
+	vh->finder_info[0] = bvh->finder_info[0] =
+		cpu_to_be32(parent_ino(dentry));
+
+	/* Bootloader */
+	vh->finder_info[1] = bvh->finder_info[1] = cpu_to_be32(inode->i_ino);
+
+	/* Per spec, the OS X system folder - same as finder_info[0] here */
+	vh->finder_info[5] = bvh->finder_info[5] =
+		cpu_to_be32(parent_ino(dentry));
+
+	mutex_unlock(&sbi->vh_mutex);
+	return 0;
+}
+
 static int hfsplus_ioctl_getflags(struct file *file, int __user *user_flags)
 {
 	struct inode *inode = file->f_path.dentry->d_inode;
@@ -108,6 +140,8 @@ long hfsplus_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 		return hfsplus_ioctl_getflags(file, argp);
 	case HFSPLUS_IOC_EXT2_SETFLAGS:
 		return hfsplus_ioctl_setflags(file, argp);
+	case HFSPLUS_IOC_BLESS:
+		return hfsplus_ioctl_bless(file, argp);
 	default:
 		return -ENOTTY;
 	}