Date: Mon, 12 May 2008 10:03:14 -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: <20080512100202.W954@desktop> In-Reply-To: <20080512101607.GC18958@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> <20080511153926.T954@desktop> <20080512101607.GC18958@deviant.kiev.zoral.com.ua>
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On Mon, 12 May 2008, Kostik Belousov wrote: > 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 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. > I use the f_cdevpriv != 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 ? No, it's not a big cost, however if it is possible to avoid that is best. Can you not check the type before checking f_cdevpriv? Should we not only be checking cdevpriv in contexts where we know that it is not a vnode? > >> >>> >>> 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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