Re: Simple Xenomai 4 API use examples and a question

[Philippe Gerum <rpm@xenomai.org>]

Emmanuel Pacaud <emmanuel.pacaud@lapp.in2p3.fr> writes:

> [1. text/markdown]
> Hi,
>
> I have started to work on a repository which is intended as a collection of very simple (dumb) examples of Xenomai 4 API use. Each example is an application, sometimes coupled with a kernel module, with the strict minimum around the actual API use. Applications and kernel modules are built using meson. The meson files are also kept the their simplest form. That was easy for the application building, not so for the kernel modules.
>
> The repository is here: <https://gitlab.com/emmanuelpacaud/xenomai-c-examples>
>
> It is similar to what I did for my own project: <https://github.com/AravisProject/aravis-c-examples>. I do think this sort a simple example collection are useful to understand how to use an API.
>
> It is a work on progress, the code should be more commented.
>
> But to be useful, all the examples should work, and I'm blocking on the oob_ioctl example :(
>
> * <https://gitlab.com/emmanuelpacaud/xenomai-c-examples/-/blob/cd9f849d4325b57565edcd691021255adc486b90/oob-ioctl.c>
> * <https://gitlab.com/emmanuelpacaud/xenomai-c-examples/-/blob/cd9f849d4325b57565edcd691021255adc486b90/modules/oob-ioctl.c>
> * <https://gitlab.com/emmanuelpacaud/xenomai-c-examples/-/blob/cd9f849d4325b57565edcd691021255adc486b90/modules/oob-ioctl.h>
>
> The ioctl call fails with a `Bad file descriptor` error. What I'm doing wrong ?
>
> Emmanuel.

EBADF is likely returned because your driver does not register the file
as an oob-capable one, therefore it won't accept oob_ioctl() requests. A
typical way to implement the missing bits would be as follows:

struct foo_state {
	struct evl_file efile;
	...
};

static int foo_open(struct inode *inode, struct file *filp)
{
	struct foo_state *st;
	int ret;

	st = kzalloc(sizeof(*st), GFP_KERNEL);
	if (st == NULL)
		return -ENOMEM;

	ret = evl_open_file(&st->efile, filp);
	if (ret)
		kfree(st);

	filp->private_data = st;

	return ret;
}

static int foo_release(struct inode *inode, struct file *filp)
{
	struct foo_state *st = filp->private_data;

	evl_release_file(&st->efile);
	kfree(st);

	return 0;
}

The way this works is explained in this document:
https://v4.xenomai.org/core/kernel-api/file/

-- 
Philippe.