Date: Tue, 13 May 2008 12:37:34 +0300 From: Kostik Belousov <kostikbel@gmail.com> To: Jeff Roberson <jroberson@jroberson.net> Cc: arch@freebsd.org Subject: Re: Per-open file private data for the cdevs Message-ID: <20080513093734.GF18958@deviant.kiev.zoral.com.ua> In-Reply-To: <20080512100202.W954@desktop> References: <20080504171002.GN18958@deviant.kiev.zoral.com.ua> <20080510214812.Y954@desktop> <20080511115030.GV18958@deviant.kiev.zoral.com.ua> <20080511115815.GW18958@deviant.kiev.zoral.com.ua> <20080511153926.T954@desktop> <20080512101607.GC18958@deviant.kiev.zoral.com.ua> <20080512100202.W954@desktop>
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--7yq/Cf0cB4WNollR Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, May 12, 2008 at 10:03:14AM -1000, Jeff Roberson wrote: >=20 > On Mon, 12 May 2008, Kostik Belousov wrote: >=20 > >On Sun, May 11, 2008 at 03:40:14PM -1000, Jeff Roberson wrote: > >> > >>On Sun, 11 May 2008, Kostik Belousov wrote: > >> > >>>On Sun, May 11, 2008 at 02:50:30PM +0300, Kostik Belousov wrote: > >>>>On Sat, May 10, 2008 at 09:53:12PM -1000, Jeff Roberson wrote: > >>>>>On Sun, 4 May 2008, Kostik Belousov wrote: > >>>>> > >>>>>>Since the review for the clone-at-open patch (fdclone) posted some= =20 > >>>>>>time > >>>>>>ago > >>>>>>mostly says that it would be better to implement per-file private d= ata > >>>>>>instead, I produced the patch along this line, > >>>>>> > >>>>>>The patch does not change the cdevsw ABI, instead, three new functi= ons > >>>>>>nt devfs_get_cdevpriv(void **datap); > >>>>>>int devfs_set_cdevpriv(void *priv, cdevpriv_dtr_t dtr); > >>>>>>void devfs_clear_cdevpriv(void); > >>>>>>are provided for manipulation of the per-file private data. > >>>>>> > >>>>>>devfs_set_cdevpriv assigns the priv as private data for the file > >>>>>>descriptor > >>>>>>which is used to initiate currently performed driver operation. dtr > >>>>>>is the function that will be called when either the last refernce to > >>>>>>the file goes away or devfs_clear_cdevpriv is called. > >>>>>> > >>>>>>devfs_get_cdevpriv is the obvious accessor. > >>>>>> > >>>>>>devfs_clear_cdevpriv allows to clear the private data for the still > >>>>>>open file. > >>>>>> > >>>>>>The synchronization of the cdev data and file private data is left > >>>>>>to the driver code, I did not found any generic helper mechanism th= at > >>>>>>could be useful there. > >>>>>> > >>>>>>Patch: > >>>>>>http://people.freebsd.org/~kib/misc/fdpriv.1.patch > >>>>>> > >>>>>>Dumb driver that shows the basic usage of the proposed KPI: > >>>>>>http://people.freebsd.org/~kib/misc/fpclone.c > >>>>>> > >>>>>>Previous version of the patch was tested by Peter Holm. > >>>>>> > >>>>> > >>>>>Hi Kostik, > >>>>> > >>>>>Are these per-instances structures intended to be used by anything= =20 > >>>>>other > >>>>>than devices? If not can we make them a union with the DTYPE_VNODE > >>>>>fields to save space? > >>>>> > >>>>>Thanks, > >>>>>Jeff > >>>> > >>>>The current version of the patch is at > >>>>http://people.freebsd.org/~kib/misc/fdpriv.3.patch > >>>> > >>>>Per insistence of John Baldwin and request of Eric Anholt, the=20 > >>>>destructors > >>>>are called now when either file is last closed, or the device is > >>>>destroyed. > >>>>This versions adds only one pointer to the struct file. > >>>> > >>>>Jeff, would you, please, explicitely specify what field you propose to > >>>>union with the f_cdevpriv ? > >> > >>f_nextoff and f_seqcount are only used if vn_read() and vn_write() are > >>used. They do not apply to any other descriptors. > >I use the f_cdevpriv !=3D NULL as an indicator for the necessity to enter > >the cdevpriv code, in particular, locking the cdevpriv_mtx, that would > >otherwise needed to be entered at each last close. I think that one > >pointer for the struct file is not too big cost, do you agree ? >=20 > No, it's not a big cost, however if it is possible to avoid that is best. >=20 > Can you not check the type before checking f_cdevpriv? Should we not onl= y=20 > be checking cdevpriv in contexts where we know that it is not a vnode? I am sorry, my english may be not enough, so I may interpret your proposal mistakenly. I read it as a suggestion to check the file type before accessing the f_cdevpriv. The problem with the f_cdevpriv exists only at the _fdrop(). There, we have a file of f_type =3D=3D DTYPE_VNODE both for devfs and normal files. I cannot check the f_vnode since the vnode may be reclaimed. The only differentiator is the f_ops, that is devfs_ops_f for devfs file, and vnops for the normal file during the file lifetime. Unfortunately, f_ops is reset to the badfileops by vn_closefile before the _fdrop() is getting called. Reserving the flag in the f_flag looks not good due to interaction with the userspace. I do not want the callback to be called before the d_close() driver method gets a chance to clean the data. >=20 > > > >> > >>> > >>>Of course, I forgot to answer the question. Yes, the KPI is supposed to > >>>be used by the drivers only. Please, note that device open files have > >>>DTYPE_VNODE. > >>> > > --7yq/Cf0cB4WNollR Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (FreeBSD) iEYEARECAAYFAkgpYV0ACgkQC3+MBN1Mb4iY0ACgvoYMcS9XS3/a9Uae1motcOiG z6AAoMWSpiZuO1wV/CtT1t2IQvydAO6w =lpEc -----END PGP SIGNATURE----- --7yq/Cf0cB4WNollR--
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