Date: Sun, 11 May 2008 15:40:14 -1000 (HST) From: Jeff Roberson <jroberson@jroberson.net> To: Kostik Belousov <kostikbel@gmail.com> Cc: arch@freebsd.org Subject: Re: Per-open file private data for the cdevs Message-ID: <20080511153926.T954@desktop> In-Reply-To: <20080511115815.GW18958@deviant.kiev.zoral.com.ua> 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>
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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 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 ? f_nextoff and f_seqcount are only used if vn_read() and vn_write() are used. They do not apply to any other descriptors. > > 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. >
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