dentry name snapshots

take_dentry_name_snapshot() takes a safe snapshot of dentry name;
if the name is a short one, it gets copied into caller-supplied
structure, otherwise an extra reference to external name is grabbed
(those are never modified).  In either case the pointer to stable
string is stored into the same structure.

dentry must be held by the caller of take_dentry_name_snapshot(),
but may be freely dropped afterwards - the snapshot will stay
until destroyed by release_dentry_name_snapshot().

Intended use:
	struct name_snapshot s;

	take_dentry_name_snapshot(&s, dentry);
	...
	access s.name
	...
	release_dentry_name_snapshot(&s);

Replaces fsnotify_oldname_...(), gets used in fsnotify to obtain the name
to pass down with event.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/dcache.c b/fs/dcache.c
index b85da8897ffacbd62fd2531f981c01ed2202f518..831f3a9a8f05282b8ba9aae9c6ed963334b9b8f3 100644 (file)
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -277,6 +277,33 @@ static inline int dname_external(const struct dentry *dentry)
        return dentry->d_name.name != dentry->d_iname;
 }
 
+void take_dentry_name_snapshot(struct name_snapshot *name, struct dentry *dentry)
+{
+       spin_lock(&dentry->d_lock);
+       if (unlikely(dname_external(dentry))) {
+               struct external_name *p = external_name(dentry);
+               atomic_inc(&p->u.count);
+               spin_unlock(&dentry->d_lock);
+               name->name = p->name;
+       } else {
+               memcpy(name->inline_name, dentry->d_iname, DNAME_INLINE_LEN);
+               spin_unlock(&dentry->d_lock);
+               name->name = name->inline_name;
+       }
+}
+EXPORT_SYMBOL(take_dentry_name_snapshot);
+
+void release_dentry_name_snapshot(struct name_snapshot *name)
+{
+       if (unlikely(name->name != name->inline_name)) {
+               struct external_name *p;
+               p = container_of(name->name, struct external_name, name[0]);
+               if (unlikely(atomic_dec_and_test(&p->u.count)))
+                       kfree_rcu(p, u.head);
+       }
+}
+EXPORT_SYMBOL(release_dentry_name_snapshot);
+
 static inline void __d_set_inode_and_type(struct dentry *dentry,
                                          struct inode *inode,
                                          unsigned type_flags)

diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
index e892ae7d89f8bc078848d8752affa1598a7e1e11..acd3be2cc691bb577916aa552668d2c1d179ed69 100644 (file)
--- a/fs/debugfs/inode.c
+++ b/fs/debugfs/inode.c
@@ -766,7 +766,7 @@ struct dentry *debugfs_rename(struct dentry *old_dir, struct dentry *old_dentry,
 {
        int error;
        struct dentry *dentry = NULL, *trap;
-       const char *old_name;
+       struct name_snapshot old_name;
 
        trap = lock_rename(new_dir, old_dir);
        /* Source or destination directories don't exist? */
@@ -781,19 +781,19 @@ struct dentry *debugfs_rename(struct dentry *old_dir, struct dentry *old_dentry,
        if (IS_ERR(dentry) || dentry == trap || d_really_is_positive(dentry))
                goto exit;
 
-       old_name = fsnotify_oldname_init(old_dentry->d_name.name);
+       take_dentry_name_snapshot(&old_name, old_dentry);
 
        error = simple_rename(d_inode(old_dir), old_dentry, d_inode(new_dir),
                              dentry, 0);
        if (error) {
-               fsnotify_oldname_free(old_name);
+               release_dentry_name_snapshot(&old_name);
                goto exit;
        }
        d_move(old_dentry, dentry);
-       fsnotify_move(d_inode(old_dir), d_inode(new_dir), old_name,
+       fsnotify_move(d_inode(old_dir), d_inode(new_dir), old_name.name,
                d_is_dir(old_dentry),
                NULL, old_dentry);
-       fsnotify_oldname_free(old_name);
+       release_dentry_name_snapshot(&old_name);
        unlock_rename(new_dir, old_dir);
        dput(dentry);
        return old_dentry;

diff --git a/fs/namei.c b/fs/namei.c
index efe53a5d0737cce7199ef5ee7205cd4669c305f7..c5588e837b1532bfc201a5b8d6bfcdedad9f107f 100644 (file)
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -4362,11 +4362,11 @@ int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
 {
        int error;
        bool is_dir = d_is_dir(old_dentry);
-       const unsigned char *old_name;
        struct inode *source = old_dentry->d_inode;
        struct inode *target = new_dentry->d_inode;
        bool new_is_dir = false;
        unsigned max_links = new_dir->i_sb->s_max_links;
+       struct name_snapshot old_name;
 
        if (source == target)
                return 0;
@@ -4413,7 +4413,7 @@ int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
        if (error)
                return error;
 
-       old_name = fsnotify_oldname_init(old_dentry->d_name.name);
+       take_dentry_name_snapshot(&old_name, old_dentry);
        dget(new_dentry);
        if (!is_dir || (flags & RENAME_EXCHANGE))
                lock_two_nondirectories(source, target);
@@ -4468,14 +4468,14 @@ out:
                inode_unlock(target);
        dput(new_dentry);
        if (!error) {
-               fsnotify_move(old_dir, new_dir, old_name, is_dir,
+               fsnotify_move(old_dir, new_dir, old_name.name, is_dir,
                              !(flags & RENAME_EXCHANGE) ? target : NULL, old_dentry);
                if (flags & RENAME_EXCHANGE) {
                        fsnotify_move(new_dir, old_dir, old_dentry->d_name.name,
                                      new_is_dir, NULL, new_dentry);
                }
        }
-       fsnotify_oldname_free(old_name);
+       release_dentry_name_snapshot(&old_name);
 
        return error;
 }

diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
index 01a9f0f007d4518563fd9ad1f06d3b48e2aa872a..0c4583b61717646e491a28d879b5762faeb8956e 100644 (file)
--- a/fs/notify/fsnotify.c
+++ b/fs/notify/fsnotify.c
@@ -161,16 +161,20 @@ int __fsnotify_parent(const struct path *path, struct dentry *dentry, __u32 mask
        if (unlikely(!fsnotify_inode_watches_children(p_inode)))
                __fsnotify_update_child_dentry_flags(p_inode);
        else if (p_inode->i_fsnotify_mask & mask) {
+               struct name_snapshot name;
+
                /* we are notifying a parent so come up with the new mask which
                 * specifies these are events which came from a child. */
                mask |= FS_EVENT_ON_CHILD;
 
+               take_dentry_name_snapshot(&name, dentry);
                if (path)
                        ret = fsnotify(p_inode, mask, path, FSNOTIFY_EVENT_PATH,
-                                      dentry->d_name.name, 0);
+                                      name.name, 0);
                else
                        ret = fsnotify(p_inode, mask, dentry->d_inode, FSNOTIFY_EVENT_INODE,
-                                      dentry->d_name.name, 0);
+                                      name.name, 0);
+               release_dentry_name_snapshot(&name);
        }
 
        dput(parent);

diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index d2e38dc6172c0670472e654103f2f0bfa0d1b2ba..025727bf679745e507bb427f14198bf1e607ae8e 100644 (file)
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -591,5 +591,11 @@ static inline struct inode *d_real_inode(const struct dentry *dentry)
        return d_backing_inode(d_real((struct dentry *) dentry, NULL, 0));
 }
 
+struct name_snapshot {
+       const char *name;
+       char inline_name[DNAME_INLINE_LEN];
+};
+void take_dentry_name_snapshot(struct name_snapshot *, struct dentry *);
+void release_dentry_name_snapshot(struct name_snapshot *);
 
 #endif /* __LINUX_DCACHE_H */

diff --git a/include/linux/fsnotify.h b/include/linux/fsnotify.h
index b43d3f5bd9ead666e4e53894e8f98bdf25fb7ad8..b78aa7ac77ce1d6920aa196f4cd71d6d6a7aee7b 100644 (file)
--- a/include/linux/fsnotify.h
+++ b/include/linux/fsnotify.h
@@ -293,35 +293,4 @@ static inline void fsnotify_change(struct dentry *dentry, unsigned int ia_valid)
        }
 }
 
-#if defined(CONFIG_FSNOTIFY)   /* notify helpers */
-
-/*
- * fsnotify_oldname_init - save off the old filename before we change it
- */
-static inline const unsigned char *fsnotify_oldname_init(const unsigned char *name)
-{
-       return kstrdup(name, GFP_KERNEL);
-}
-
-/*
- * fsnotify_oldname_free - free the name we got from fsnotify_oldname_init
- */
-static inline void fsnotify_oldname_free(const unsigned char *old_name)
-{
-       kfree(old_name);
-}
-
-#else  /* CONFIG_FSNOTIFY */
-
-static inline const char *fsnotify_oldname_init(const unsigned char *name)
-{
-       return NULL;
-}
-
-static inline void fsnotify_oldname_free(const unsigned char *old_name)
-{
-}
-
-#endif /*  CONFIG_FSNOTIFY */
-
 #endif /* _LINUX_FS_NOTIFY_H */