From 787fb6bc9682ec7c05fb5d9561b57100fbc1cc41 Mon Sep 17 00:00:00 2001
From: Miklos Szeredi <mszeredi@suse.cz>
Date: Fri, 24 Oct 2014 00:14:36 +0200
Subject: [PATCH] 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: Miklos Szeredi <mszeredi@suse.cz>
---
fs/namei.c | 14 ++++++++++++++
include/linux/fs.h | 11 +++++++++++
2 files changed, 25 insertions(+)
diff --git a/fs/namei.c b/fs/namei.c
index 77fd536106cb..d20191c0ebf5 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -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);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 55cc0a319baa..69118b3cb917 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -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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