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Subject[PATCH 09/32] whiteout: Add vfs_whiteout() and whiteout inode operation
Date
Simply white-out a given directory entry. This functionality is usually used
in the sense of unlink. Therefore the given dentry can still be in-use and
contains an in-use inode. The filesystems inode operation has to do what
unlink or rmdir would in that case. Since the dentry still might be in-use
we have to provide a fresh unhashed dentry that is used as the whiteout
dentry instead. The given dentry is dropped and the whiteout dentry is
rehashed instead.

Signed-off-by: Jan Blunck <jblunck@suse.de>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: Valerie Aurora (Henson) <vaurora@redhat.com>
---
fs/dcache.c | 4 +-
fs/namei.c | 104 ++++++++++++++++++++++++++++++++++++++++++++++++
include/linux/dcache.h | 7 +++-
include/linux/fs.h | 3 +
4 files changed, 116 insertions(+), 2 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index 8bfbcd7..9260c99 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1076,8 +1076,10 @@ struct dentry *d_alloc_name(struct dentry *parent, const char *name)
/* the caller must hold dcache_lock */
static void __d_instantiate(struct dentry *dentry, struct inode *inode)
{
- if (inode)
+ if (inode) {
+ dentry->d_flags &= ~DCACHE_WHITEOUT;
list_add(&dentry->d_alias, &inode->i_dentry);
+ }
dentry->d_inode = inode;
fsnotify_d_instantiate(dentry, inode);
}
diff --git a/fs/namei.c b/fs/namei.c
index e19fa2b..9cab708 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2111,6 +2111,110 @@ SYSCALL_DEFINE2(mkdir, const char __user *, pathname, int, mode)
return sys_mkdirat(AT_FDCWD, pathname, mode);
}

+
+/* Checks on the victim for whiteout */
+static inline int may_whiteout(struct inode *dir, struct dentry *victim,
+ int isdir)
+{
+ int err;
+
+ /* from may_create() */
+ if (IS_DEADDIR(dir))
+ return -ENOENT;
+ err = inode_permission(dir, MAY_WRITE | MAY_EXEC);
+ if (err)
+ return err;
+
+ /* from may_delete() */
+ if (IS_APPEND(dir))
+ return -EPERM;
+ if (!victim->d_inode)
+ return 0;
+ if (check_sticky(dir, victim->d_inode) ||
+ IS_APPEND(victim->d_inode) ||
+ IS_IMMUTABLE(victim->d_inode))
+ return -EPERM;
+ if (isdir) {
+ if (!S_ISDIR(victim->d_inode->i_mode))
+ return -ENOTDIR;
+ if (IS_ROOT(victim))
+ return -EBUSY;
+ } else if (S_ISDIR(victim->d_inode->i_mode))
+ return -EISDIR;
+ if (victim->d_flags & DCACHE_NFSFS_RENAMED)
+ return -EBUSY;
+ return 0;
+}
+
+/**
+ * vfs_whiteout: creates a white-out for the given directory entry
+ * @dir: parent inode
+ * @dentry: directory entry to white-out
+ *
+ * Simply white-out a given directory entry. This functionality is usually used
+ * in the sense of unlink. Therefore the given dentry can still be in-use and
+ * contains an in-use inode. The filesystem has to do what unlink or rmdir
+ * would in that case. Since the dentry still might be in-use we have to
+ * provide a fresh unhashed dentry that whiteout can fill the new inode into.
+ * In that case the given dentry is dropped and the fresh dentry containing the
+ * whiteout is rehashed instead. If the given dentry is unused, the whiteout
+ * inode is instantiated into it instead.
+ *
+ * After this returns with success, don't make any assumptions about the inode.
+ * Just dput() it dentry.
+ */
+int vfs_whiteout(struct inode *dir, struct dentry *dentry, int isdir)
+{
+ int err;
+ struct inode *old_inode = dentry->d_inode;
+ struct dentry *parent, *whiteout;
+
+ err = may_whiteout(dir, dentry, isdir);
+ if (err)
+ return err;
+
+ BUG_ON(dentry->d_parent->d_inode != dir);
+
+ if (!dir->i_op || !dir->i_op->whiteout)
+ return -EOPNOTSUPP;
+
+ if (old_inode) {
+ vfs_dq_init(dir);
+
+ mutex_lock(&old_inode->i_mutex);
+ if (isdir)
+ dentry_unhash(dentry);
+ if (d_mountpoint(dentry))
+ err = -EBUSY;
+ else {
+ if (isdir)
+ err = security_inode_rmdir(dir, dentry);
+ else
+ err = security_inode_unlink(dir, dentry);
+ }
+ }
+
+ parent = dget_parent(dentry);
+ whiteout = d_alloc_name(parent, dentry->d_name.name);
+
+ if (!err)
+ err = dir->i_op->whiteout(dir, dentry, whiteout);
+
+ if (old_inode) {
+ mutex_unlock(&old_inode->i_mutex);
+ if (!err) {
+ fsnotify_link_count(old_inode);
+ d_delete(dentry);
+ }
+ if (isdir)
+ dput(dentry);
+ }
+
+ dput(whiteout);
+ dput(parent);
+ return err;
+}
+
/*
* We try to drop the dentry early: we should have
* a usage count of 2 if we're the only user of this
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index c66d224..e00e95b 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -181,8 +181,8 @@ d_iput: no no no yes
#define DCACHE_UNHASHED 0x0010

#define DCACHE_INOTIFY_PARENT_WATCHED 0x0020 /* Parent inode is watched */
-
#define DCACHE_COOKIE 0x0040 /* For use by dcookie subsystem */
+#define DCACHE_WHITEOUT 0x0080 /* This negative dentry is a whiteout */

extern spinlock_t dcache_lock;
extern seqlock_t rename_lock;
@@ -351,6 +351,11 @@ static inline int d_unhashed(struct dentry *dentry)
return (dentry->d_flags & DCACHE_UNHASHED);
}

+static inline int d_is_whiteout(struct dentry *dentry)
+{
+ return (dentry->d_flags & DCACHE_WHITEOUT);
+}
+
static inline struct dentry *dget_parent(struct dentry *dentry)
{
struct dentry *ret;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 92734c0..5950616 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -141,6 +141,7 @@ struct inodes_stat_t {
#define MS_RELATIME (1<<21) /* Update atime relative to mtime/ctime. */
#define MS_KERNMOUNT (1<<22) /* this is a kern_mount call */
#define MS_I_VERSION (1<<23) /* Update inode I_version field */
+#define MS_WHITEOUT (1<<26) /* fs does support white-out filetype */
#define MS_ACTIVE (1<<30)
#define MS_NOUSER (1<<31)

@@ -1241,6 +1242,7 @@ extern int vfs_link(struct dentry *, struct inode *, struct dentry *);
extern int vfs_rmdir(struct inode *, struct dentry *);
extern int vfs_unlink(struct inode *, struct dentry *);
extern int vfs_rename(struct inode *, struct dentry *, struct inode *, struct dentry *);
+extern int vfs_whiteout(struct inode *, struct dentry *, int);

/*
* VFS dentry helper functions.
@@ -1345,6 +1347,7 @@ struct inode_operations {
int (*mkdir) (struct inode *,struct dentry *,int);
int (*rmdir) (struct inode *,struct dentry *);
int (*mknod) (struct inode *,struct dentry *,int,dev_t);
+ int (*whiteout) (struct inode *, struct dentry *, struct dentry *);
int (*rename) (struct inode *, struct dentry *,
struct inode *, struct dentry *);
int (*readlink) (struct dentry *, char __user *,int);
--
1.6.1.3


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