object_set_cookie - Set an object's cookie.


#include <magenta/syscalls.h>

mx_status_t mx_object_set_cookie(mx_handle_t handle, mx_handle_t scope, uint64_t cookie);


Some objects (Events, Event pairs, Resources, VMOs) may have a Cookie attached, which is a 64bit opaque value. Initially the Cookie is undefined and not readable.

Once mx_object_set_cookie() is called successfully, the cookie is set, and the Object referenced by the scope handle becomes the key necessary to read the cookie or modify it. The scope may never be changed for the lifetime of the object.

Event pairs are special. If one side of the pair is closed, the other side's cookie is invalidated. An invalidated cookie is not get-able or set-able with any scope.

Cookies are useful for objects that will be passed to another process and later returned. By setting the cookie with mx_object_set_cookie(), using a scope that is not accessible by other processes, mx_object_get_cookie() may later be used to verify that a handle is referring to an object that was “created” by the calling process and simultaneously return an ID or pointer to local state for that object.

When the object referenced by scope is destroyed or if a handle to that object is no longer available, the cookie may no longer be modified or obtained.


mx_object_set_cookie() returns MX_OK on success. In the event of failure, a negative error value is returned.


MX_ERR_BAD_HANDLE handle or scope are not valid handles.

MX_ERR_NOT_SUPPORTED handle is not a handle to an object that may have a cookie set.

MX_ERR_ACCESS_DENIED mx_object_set_cookie() was called previously with a different object as the scope, or the cookie has not been set.