Date: Sat, 10 May 2008 21:53:12 -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: <20080510214812.Y954@desktop> In-Reply-To: <20080504171002.GN18958@deviant.kiev.zoral.com.ua> References: <20080504171002.GN18958@deviant.kiev.zoral.com.ua>
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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
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