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>
diff --git a/fs/namei.c b/fs/namei.c
index 77fd536..d20191c 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -4346,6 +4346,20 @@
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);