Date: Wed, 29 Aug 2012 07:12:40 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: Luigi Rizzo <rizzo@iet.unipi.it> Cc: Andriy Gapon <avg@freebsd.org>, freebsd-current@freebsd.org, current@freebsd.org Subject: Re: per file descriptor device callbacks ? Message-ID: <20120829041240.GT33100@deviant.kiev.zoral.com.ua> In-Reply-To: <20120828184226.GB68683@onelab2.iet.unipi.it> References: <20120827073403.GA49223@onelab2.iet.unipi.it> <201208271227.54785.jhb@freebsd.org> <20120828155025.GA66068@onelab2.iet.unipi.it> <201208281240.29612.jhb@freebsd.org> <20120828172606.GR33100@deviant.kiev.zoral.com.ua> <20120828184226.GB68683@onelab2.iet.unipi.it>
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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.
> >=20
> > 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.
> >=20
> > Also, MGTDEVICE does track the mappings of the pages, so you can clean
> > up on device destruction.
>=20
> 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.
>=20
> > Normal callbacks of the device pager allows to execute ctr/dtr methods
> > at the time of mapping creation and tear down.
>=20
> 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.
>=20
> static struct cdev_pager_ops saved_cdev_pager_ops;
> static struct cdev_pager_ops netmap_cdev_pager_ops;
>=20
> 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);
> }
>=20
>=20
> 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;
> =20
> /* XXX check size etc. */
> obj =3D vm_pager_allocate(OBJT_DEVICE, cdev, objsize, prot, *foff,
> curthread->td_ucred);
Use cdev_pager_allocate().
> if (obj =3D=3D NULL)
> return EINVAL;
> if (saved_cdev_pager_ops.cdev_pg_fault =3D=3D 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 =3D *(obj->un_pager.devp.ops);
> netmap_cdev_pager_ops =3D *(obj->un_pager.devp.ops);
> netmap_cdev_pager_ops.cdev_pg_dtor =3D netmap_dev_pager_d=
tor;
> };
> obj->un_pager.devp.ops =3D &netmap_cdev_pager_ops;
> *objp =3D obj;
> /* XXX perhaps do something more here, such as install
> * mappings for the pages so we have no faults later.
> */
> return 0;
> }
>=20
> static struct cdevsw netmap_cdevsw =3D {
> .d_version =3D D_VERSION,
> .d_name =3D "netmap",
> .d_open =3D netmap_open,
> .d_mmap =3D netmap_mmap,
> .d_mmap_single =3D netmap_mmap_single,
> .d_ioctl =3D netmap_ioctl,
> .d_poll =3D netmap_poll,
> .d_close =3D netmap_close,
> };
>=20
> cheers
> luigi
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