OK thanks. I am attaching a proposed patch for the docs. I've tried to use
the syntax of the Linux Device Drivers book.
I will soon submit a more complete pair of test apps for using mmap(),
which I assume would end up in xenomai-3.x/demo/cobalt/.
thanks,
-C Smith
On Thu, Oct 21, 2021 at 8:23 AM Jan Kiszka <jan.kis...@siemens.com> wrote:
> On 20.10.21 07:49, C Smith via Xenomai wrote:
> > I recently got a Xenomai 3.1 shared memory .mmap op to work but I don't
> see
> > any mmap examples in the Xemomai documentation (please publish one). I
> have
> > a question as to why I had to do it a certain way. Here is the
> > (abbreviated) code I used:
> >
> > typedef struct { // shared struct
> > int data[PAGE_SIZE*4];
> > } shm_test_t;
> >
> > shm_test_t *shm_test_p = 0; // create a driver struct to share
> > shm_test_p = kmalloc(sizeof(shm_test_t) + RTDM_MAX_DEVNAME_LEN,
> > GFP_KERNEL);
> >
> > static struct rtdm_driver device_tmpl = {
> > .profile_info =
> > RTDM_PROFILE_INFO(mydev_,RTDM_CLASS_EXPERIMENTAL,0,999),
> > .device_flags = RTDM_NAMED_DEVICE | RTDM_EXCLUSIVE,
> > .device_count = MAX_DEVICES,
> > .context_size = sizeof(struct mydev_context),
> > .ops = {
> > .open = mydev_open,
> > .close = mydev_close,
> > .read_nrt = mydev_read,
> > .ioctl_rt = mydev_ioctl,
> > .ioctl_nrt = mydev_ioctl,
> > .mmap = mydev_mmap,
> > },
> > };
> >
> > // device initialization
> > dev = kmalloc(sizeof(struct rtdm_device) + RTDM_MAX_DEVNAME_LEN,
> > GFP_KERNEL);
> > dev->driver = &device_tmpl;
> > dev->label = "mydev%d";
> > name = (char *)(dev + 1);
> > ksformat(name, RTDM_MAX_DEVNAME_LEN, dev->label, i);
> > err = rtdm_dev_register(dev);
> >
> > // .mmap op handler
> > int mydev_mmap(struct rtdm_fd *fd, struct vm_area_struct *vma)
> > {
> > rtdm_mmap_kmem(vma, shm_test_p); // do the address conversion
> > }
> >
> > That works. I can share the shm_test_t struct between my rtdm driver and
> > userspace.
> > In userspace I do:
> > mydev_fd = open("/dev/rtdm/mydev0", O_RDWR); // linked against Xeno3.1
> > posix wrappers
> > shmem_data_p = (shm_test_t *)
> > mmap(0,sizeof(shm_test_t),PROT_READ|PROT_WRITE,MAP_SHARED,mydev_fd,0);
> >
> > That works, but why don't I need rtdm_mmap_to_user() in the .mmap op
> > handler? If rtdm_mmap_kmem() does the job then why does
> rtdm_mmap_to_user()
> > exist?
>
> rtdm_mmap_to_user is only foreseen for cases outside of an mmap handler,
> typically in some specific ioctl (see e.g.
> kernel/drivers/analogy/buffer.c). Most cases a better and more
> consistently handled via mmap handler and, thus, mmap() syscalls. We can
> improve the documentation on this cases. For rtdm_mmap_{k,v,io}mem, the
> situation should be better already.
>
> In any case, patches welcome.
>
> Jan
>
> --
> Siemens AG, T RDA IOT
> Corporate Competence Center Embedded Linux
>
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