Date: Mon, 12 May 2008 13:16:07 +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: <20080512101607.GC18958@deviant.kiev.zoral.com.ua> In-Reply-To: <20080511153926.T954@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>
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--bneO9ZV9xXj8K50n Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Sun, May 11, 2008 at 03:40:14PM -1000, Jeff Roberson wrote: >=20 > On Sun, 11 May 2008, Kostik Belousov wrote: >=20 > >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 ti= me=20 > >>>>ago > >>>>mostly says that it would be better to implement per-file private data > >>>>instead, I produced the patch along this line, > >>>> > >>>>The patch does not change the cdevsw ABI, instead, three new functions > >>>>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=20 > >>>>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 that > >>>>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 oth= er > >>>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 destruct= ors > >>are called now when either file is last closed, or the device is=20 > >>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 ? >=20 > f_nextoff and f_seqcount are only used if vn_read() and vn_write() are=20 > 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 > > > >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. > > --bneO9ZV9xXj8K50n Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (FreeBSD) iEYEARECAAYFAkgoGOcACgkQC3+MBN1Mb4iVlgCgv214NkFsa0JOpgyYvoY0mMEW vlMAoNpMa/7hrTIR8QQaTWaGfvKhhhht =Ypph -----END PGP SIGNATURE----- --bneO9ZV9xXj8K50n--
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