Re: per file descriptor device callbacks ?

On Tue, Aug 28, 2012 at 08:26:06PM +0300, Konstantin Belousov wrote:
...
> > dev_clone() is rather gross and a lot harder to use than
> > devfs_set_cdevpriv().  If you are fine with the inherent problems
> > of the device pager (you can't ever make mappings go away), you can
> > just assign each client a unique offset into your shared object's
> > memory space.  However, if you are exporting shared memory buffers,
> > then a better model might be to let your clients use
> > shm_open(SHM_ANON) to create buffers, then pass them into your driver
> > via an ioctl() and use shm_map() to map them into the kernel.
> 
> Well, there is a new OBJT_MGTDEVICE pager, which together with
> d_mmap_single() allows to have even per-mapping data. i915kms uses it.
> You do not need cdevpriv for the per-mapping data.
> 
> Also, MGTDEVICE does track the mappings of the pages, so you can clean
> up on device destruction.

interesting, thanks for the pointer, i'll look it up in i915kms.
Does this exist also in stable/9 ?
It would be a shame otherwise...

> Normal callbacks of the device pager allows to execute ctr/dtr methods
> at the time of mapping creation and tear down.

what would be a good way to install my own ctr/dtr methods ?
I only found out a rather crude one, and it only works for
the destructor:

    static struct cdev_pager_ops saved_cdev_pager_ops;
    static struct cdev_pager_ops netmap_cdev_pager_ops;

    static void
    netmap_dev_pager_dtor(void *handle)
    {
        saved_cdev_pager_ops.cdev_pg_dtor(handle);
	// my code here
        D("ready to release memory for %p", handle);
    }


    static int
    netmap_mmap_single(struct cdev *cdev, vm_ooffset_t *foff,
		vm_size_t objsize,  vm_object_t *objp, int prot)
    {
        vm_object_t obj;
 
	/* XXX check size etc. */
        obj = vm_pager_allocate(OBJT_DEVICE, cdev, objsize, prot, *foff,
            curthread->td_ucred);
        if (obj == NULL)
                return EINVAL;
        if (saved_cdev_pager_ops.cdev_pg_fault == NULL) {
                D("initialize cdev_pager_ops");
                saved_cdev_pager_ops = *(obj->un_pager.devp.ops);
                netmap_cdev_pager_ops = *(obj->un_pager.devp.ops);
                netmap_cdev_pager_ops.cdev_pg_dtor = netmap_dev_pager_dtor;
        };
        obj->un_pager.devp.ops = &netmap_cdev_pager_ops;
        *objp = obj;
	/* XXX perhaps do something more here, such as install
	 * mappings for the pages so we have no faults later.
	 */
        return 0;
    }

    static struct cdevsw netmap_cdevsw = {
        .d_version = D_VERSION,
        .d_name = "netmap",
        .d_open = netmap_open,
        .d_mmap = netmap_mmap,
        .d_mmap_single = netmap_mmap_single,
        .d_ioctl = netmap_ioctl,
        .d_poll = netmap_poll,
        .d_close = netmap_close,
    };

cheers
luigi