tree b4ab96fd8300dd73a398a7d587f8839fa052c03b
parent a8e2b6367794e6cee9eecba6d5ff425f338e0754
author Al Viro <viro@zeniv.linux.org.uk> 1499453479 -0400
committer Al Viro <viro@zeniv.linux.org.uk> 1499472550 -0400

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>