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| author | Miklos Szeredi <mszeredi@suse.cz> | 2014-10-24 02:14:36 +0400 |
|---|---|---|
| committer | Miklos Szeredi <mszeredi@suse.cz> | 2014-10-24 02:14:36 +0400 |
| commit | 787fb6bc9682ec7c05fb5d9561b57100fbc1cc41 (patch) | |
| tree | fde11fbe9f87e95ef6078fcbfed5f55c9ba134f8 | |
| parent | cbdf35bcb833bfd00f0925d7a9a33a21f41ea582 (diff) | |
| download | linux-787fb6bc9682ec7c05fb5d9561b57100fbc1cc41.tar.xz | |
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>
| -rw-r--r-- | fs/namei.c | 14 | ||||
| -rw-r--r-- | include/linux/fs.h | 11 |
2 files changed, 25 insertions, 0 deletions
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 @@ -223,6 +223,13 @@ 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 @@ -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 * |