Date: Sun, 11 May 2008 14:58:15 +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: <20080511115815.GW18958@deviant.kiev.zoral.com.ua> In-Reply-To: <20080511115030.GV18958@deviant.kiev.zoral.com.ua> References: <20080504171002.GN18958@deviant.kiev.zoral.com.ua> <20080510214812.Y954@desktop> <20080511115030.GV18958@deviant.kiev.zoral.com.ua>
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[-- Attachment #1 --] 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 time 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 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 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 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 ? 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. [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (FreeBSD) iEYEARECAAYFAkgm31cACgkQC3+MBN1Mb4hZFgCgg3EoqJOLVqCdzU20iDUZUbCl MfcAoJsv6jMtdtAt/wm6tFLviWIHRveR =qE5J -----END PGP SIGNATURE-----
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