From: Miklos Szeredi <mszeredi@xxxxxxx>
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@xxxxxxx>
---
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 1039eef0e22c..413d7c138e95 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -4323,6 +4323,20 @@ 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 9d821253379d..88ec7a2878bc 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -221,6 +221,13 @@ typedef void (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
#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.
* Also, in this manner, a Filesystem can look at only the values it cares
@@ -1387,6 +1394,7 @@ 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.
@@ -1611,6 +1619,9 @@ 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
*
--
1.8.1.4
--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
