I have inserted some answers below.
/ Raimo Niskanen, Erlang/OTP
Vance Shipley wrote:
>
> I am putting together a dynamically linked and have seen some conflict
> between the documentation and the header file erl_driver.h.
>
> erl_driver.h:
>
> typedef struct erl_drv_entry {
> int (*init)(void); /* called at system start up for statically
> linked drivers, and after loading for
> dynamically loaded drivers */
> ...
>
> That makes sense however the erl_ddll documentation says:
>
> The init function in struct driver_entry is not used anymore. After the driver
> is loaded, the function struct driver_entry *driver_init(void *) is called with
> handle as argument. If the operating system loader cannot find a function called
> driver_init, the driver will not be loaded.
>
Well, the text should say that the init function in struct driver_entry
is not _needed_ anymore. It it _is_, however, called, so there are two
functions for the same purpose - confusion. Alas! I am sorry.
For statically linked drivers only the struct driver_entry init function
is called, and for dynamically linked drivers both are called. Since it
is tricky to get a statically linked driver into the runtime system,
this matter may be of small importance.
> Now even to further muddy the waters erl_driver.h has:
>
> /*
> * This macro is used to name a dynamic driver's init function in
> * a way that doesn't lead to conflicts. This is crucial when using
> * operating systems that has one namespace for all symbols
> * (e.g. VxWorks). Example: if you have an dynamic driver C source
> * file named echo_drv.c, you use the macro like this:
> *
> * DRIVER_INIT(echo_drv)
> * {
> * ....
> * }
> *
> * This function well be called by the Erlang I/O system when the driver is load
> ed.
> * It must initialize a ErlDrvEntry structure and return a pointer to it.
> */
>
> #if defined(VXWORKS)
> # define DRIVER_INIT(DRIVER_NAME) ErlDrvEntry* DRIVER_NAME ## _init(void)
> #elif defined(__WIN32__)
> # define DRIVER_INIT(DRIVER_NAME) __declspec(dllexport) ErlDrvEntry* driver_i
> nit(void)
> #else
> # define DRIVER_INIT(DRIVER_NAME) ErlDrvEntry* driver_init(void)
> #endif
>
> So which is it? What does myt function get named in my_drv.c and what
> value do I give my_drv_entry.init?
>
> -Vance
If I dare guess You do not compile for VxWorks then Your init function
will be named driver_init. In the event I am wrong, it will be named
my_drv_init.
In R7, it is allowed (i reccon) to set my_drv_entry.init to NULL, and it
will not be called be skipped. This was not allowed earlier, since
setting my_drv_entry.init to a function that does nothing is not hard.
The important is that driver_init must return the address to Your
initialized struct my_drv_entry.