Re: [PATCH 1/2] Introduce get_ioengine for external engines

[Jens Axboe <axboe@kernel.dk>]

On 2014-02-12 12:13, Daniel Gollub wrote:
> This makes life easier for plugins written in C++
> since they do not need to deal with struct initilization issues
> with the ioengine_ops symbol.
>
> With g++ a non-static ioengine_ops in global scope like this:
>
> struct ioengine_ops ioengine = {
>          .name           = "null",
>          .version        = FIO_IOOPS_VERSION,
>          .queue          = fio_null_queue,
>          .commit         = fio_null_commit,
> };
>
> Results in:
>
> cpp_null2.cc: At global scope:
> cpp_null2.cc:112:1: error: C99 designator ‘name’ outside aggregate initializer
> cpp_null2.cc:112:1: sorry, unimplemented: non-trivial designated initializers not supported
> cpp_null2.cc:112:1: sorry, unimplemented: non-trivial designated initializers not supported
> cpp_null2.cc:112:1: sorry, unimplemented: non-trivial designated initializers not supported
> cpp_null2.cc:112:1: sorry, unimplemented: non-trivial designated initializers not supported
> $
>
> Example get_iongine() symbol usage:
>
> ---8<---
> extern "C" {
> void get_ioengine(struct ioengine_ops **ioengine_ptr) {
>          struct ioengine_ops *ioengine;
>          *ioengine_ptr = (struct ioengine_ops *) malloc(sizeof(struct ioengine_ops));
>          ioengine = *ioengine_ptr;
>
>          strcpy(ioengine->name, "cpp_null");
>          ioengine->version        = FIO_IOOPS_VERSION;
>          ioengine->queue          = fio_null_queue;
>          ioengine->commit         = fio_null_commit;
>          ioengine->getevents      = fio_null_getevents;
>          ioengine->event          = fio_null_event;
>          ioengine->init           = fio_null_init;
>          ioengine->cleanup        = fio_null_cleanup;
>          ioengine->open_file      = fio_null_open;
>          ioengine->flags          = FIO_DISKLESSIO;
> }
> }
> --->8---
>
> Signed-off-by: Daniel Gollub <d.gollub@telekom.de>
> ---
>   ioengines.c |   14 ++++++++++++++
>   1 file changed, 14 insertions(+)
>
> diff --git a/ioengines.c b/ioengines.c
> index d71e372..c080da3 100644
> --- a/ioengines.c
> +++ b/ioengines.c
> @@ -90,6 +90,7 @@ static struct ioengine_ops *dlopen_ioengine(struct thread_data *td,
>   {
>   	struct ioengine_ops *ops;
>   	void *dlhandle;
> +	typedef void (*get_ioengine_t)(struct ioengine_ops **);
>
>   	dprint(FD_IO, "dload engine %s\n", engine_lib);
>
> @@ -107,6 +108,19 @@ static struct ioengine_ops *dlopen_ioengine(struct thread_data *td,
>   	ops = dlsym(dlhandle, engine_lib);
>   	if (!ops)
>   		ops = dlsym(dlhandle, "ioengine");
> +
> +	/*
> +	 * For some external engines (like C++ ones) it is not that trivial
> +	 * to provide a non-static ionengine structure that we can reference.
> +	 * Instead we call a method which allocates the required ioengine
> +	 * structure.
> +	 */
> +	if (!ops) {
> +		get_ioengine_t get_ioengine = dlsym(dlhandle, "get_ioengine");
> +		if (get_ioengine)
> +			get_ioengine(&ops);
> +	}
> +
>   	if (!ops) {
>   		td_vmsg(td, -1, dlerror(), "dlsym");
>   		dlclose(dlhandle);
>

This looks fine, but lets put that typedef in ioengine.h instead.

-- 
Jens Axboe