Commit 787fb6bc authored by Miklos Szeredi's avatar Miklos Szeredi
Browse files

vfs: add whiteout support 



Whiteout isn't actually a new file type, but is represented as a char
device (Linus's idea) with 0/0 device number.

This has several advantages compared to introducing a new whiteout file
type:

 - no userspace API changes (e.g. trivial to make backups of upper layer
   filesystem, without losing whiteouts)

 - no fs image format changes (you can boot an old kernel/fsck without
   whiteout support and things won't break)

 - implementation is trivial

Signed-off-by: default avatarMiklos Szeredi <mszeredi@suse.cz>
parent cbdf35bc

fs/namei.c

+14 −0
Original line number Diff line number Diff line
@@ -4346,6 +4346,20 @@ SYSCALL_DEFINE2(rename, const char __user *, oldname, const char __user *, newna 
	return sys_renameat2(AT_FDCWD, oldname, AT_FDCWD, newname, 0);

}



int vfs_whiteout(struct inode *dir, struct dentry *dentry)

{

	int error = may_create(dir, dentry);

	if (error)

		return error;



	if (!dir->i_op->mknod)

		return -EPERM;



	return dir->i_op->mknod(dir, dentry,

				S_IFCHR | WHITEOUT_MODE, WHITEOUT_DEV);

}

EXPORT_SYMBOL(vfs_whiteout);



int readlink_copy(char __user *buffer, int buflen, const char *link)

{

	int len = PTR_ERR(link);

include/linux/fs.h

+11 −0
Original line number Diff line number Diff line
@@ -222,6 +222,13 @@ typedef void (dio_iodone_t)(struct kiocb *iocb, loff_t offset, 
#define ATTR_OPEN	(1 << 15) /* Truncating from open(O_TRUNC) */

#define ATTR_TIMES_SET	(1 << 16)



/*

 * Whiteout is represented by a char device.  The following constants define the

 * mode and device number to use.

 */

#define WHITEOUT_MODE 0

#define WHITEOUT_DEV 0



/*

 * This is the Inode Attributes structure, used for notify_change().  It

 * uses the above definitions as flags, to know which values have changed.
@@ -1398,6 +1405,7 @@ extern int vfs_link(struct dentry *, struct inode *, struct dentry *, struct ino 
extern int vfs_rmdir(struct inode *, struct dentry *);

extern int vfs_unlink(struct inode *, struct dentry *, struct inode **);

extern int vfs_rename(struct inode *, struct dentry *, struct inode *, struct dentry *, struct inode **, unsigned int);

extern int vfs_whiteout(struct inode *, struct dentry *);



/*

 * VFS dentry helper functions.
@@ -1628,6 +1636,9 @@ struct super_operations { 
#define IS_AUTOMOUNT(inode)	((inode)->i_flags & S_AUTOMOUNT)

#define IS_NOSEC(inode)		((inode)->i_flags & S_NOSEC)



#define IS_WHITEOUT(inode)	(S_ISCHR(inode->i_mode) && \

				 (inode)->i_rdev == WHITEOUT_DEV)



/*

 * Inode state bits.  Protected by inode->i_lock

 *

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