Date: Wed, 29 Aug 2012 13:23:29 +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: <20120829102329.GZ33100@deviant.kiev.zoral.com.ua> In-Reply-To: <20120829045526.GA75216@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> <20120829041240.GT33100@deviant.kiev.zoral.com.ua> <20120829045526.GA75216@onelab2.iet.unipi.it>
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--g2oeex4xcrwBLAZl Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Aug 29, 2012 at 06:55:26AM +0200, Luigi Rizzo wrote: > On Wed, Aug 29, 2012 at 07:12:40AM +0300, Konstantin Belousov wrote: > > 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 c= an > > > > > just assign each client a unique offset into your shared object's > > > > > memory space. However, if you are exporting shared memory buffer= s, > > > > > then a better model might be to let your clients use > > > > > shm_open(SHM_ANON) to create buffers, then pass them into your dr= iver > > > > > 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 cl= ean > > > > 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 > > >=20 > > > > Normal callbacks of the device pager allows to execute ctr/dtr meth= ods > > > > 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 > > >=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(). > >=20 > > > 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. >=20 > First and foremost, I am trying to do things without > requiring kernel modifications. This is strange. >=20 > I am trying to reuse the constructor and destructor of the standard > device pager, and around those add my own calls. Those methods are > declared static in sys/vm/device_pager.c so i cannot invoke directly > cdev_pager_allocate(). I fail to see how can you use old_dev_pager_{ctor,dtor} without also using the d_mmap. Note that use of d_mmap _does not_ mean that access to the mapped area never faults. I suggest you to go fully 'mgmt device pager' route. >=20 > I could indeed rewrite the body of those three methods > (ctor, dtor, fault) in my own code. I will look at this today. > Perhaps I could even try to install all mappings at mmap() time so > I never need to fault. >=20 > Thanks again for the suggestions >=20 > cheers > luigi >=20 >=20 > > > 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_pag= er_dtor; > > > }; > > > 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 >=20 --g2oeex4xcrwBLAZl Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (FreeBSD) iEYEARECAAYFAlA97aEACgkQC3+MBN1Mb4hQcwCfcChxtRndLaHjsGA559tJlu8X 2UEAn2GPyuv1FIRYLuNFYOmZXHPZ+7tI =aNyB -----END PGP SIGNATURE----- --g2oeex4xcrwBLAZl--
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