per file descriptor device callbacks ?
Konstantin Belousov
kostikbel at gmail.com
Wed Aug 29 04:12:45 UTC 2012
On Tue, Aug 28, 2012 at 08:42:26PM +0200, Luigi Rizzo wrote:
> 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...
Yes, it was merged.
>
> > 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:
See below.
>
> 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);
Use cdev_pager_allocate().
> if (obj == NULL)
> return EINVAL;
> if (saved_cdev_pager_ops.cdev_pg_fault == NULL) {
I do not understand what are you trying to accomplish with the
check and reinitialization, but I assume that cdev_pager_allocate()
would take care of it.
> 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
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