Date: Mon, 5 May 2008 17:20:51 +0300 From: Kostik Belousov <kostikbel@gmail.com> To: John Baldwin <jhb@freebsd.org> Cc: freebsd-arch@freebsd.org Subject: Re: Per-open file private data for the cdevs Message-ID: <20080505142051.GS18958@deviant.kiev.zoral.com.ua> In-Reply-To: <200805050939.42425.jhb@freebsd.org> References: <20080504171002.GN18958@deviant.kiev.zoral.com.ua> <200805050939.42425.jhb@freebsd.org>
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--vb/P15UJLYd8hx0q Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, May 05, 2008 at 09:39:42AM -0400, John Baldwin wrote: > On Sunday 04 May 2008 01:10:02 pm 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 descri= ptor > > 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. >=20 > I like this very much and will use it instead of devfs cloning in ipmi(4)= so=20 > we can use ipmievd when it is committed. IWBN if there was a more automa= ted=20 > way of handling the unload race, for example if destroy_dev() could someh= ow=20 > clear all the per-open fd data. That may not be easily feasible, however= . =20 > (In theory each cdev could have a list of "attached" 'struct file' object= s=20 > that it updates in VOP_CLOSE() and for a destroy dev it detaches all the= =20 > private data after marking the cdev with a bad/null cdevsw, however, that= =20 > would bloat 'struct file' with at least one more pointer (if not two).) Probably, I shall clarify that the dtr is called when the last reference to the struct file going away, unless the priv data is already cleared by the call to the devfs_clear_cdevpriv. The problem with VOP_CLOSE() is that some actions (like forced unmount or revoke) may cause less calls to the devfs_close then the files pointing to the cdev. Your proposal basically means that we need, besides the normal pointers file->vnode->cdev, have the reverse path cdev->file. I think this is ugly and better be handled by the fdrop(). --vb/P15UJLYd8hx0q Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (FreeBSD) iEYEARECAAYFAkgfF8IACgkQC3+MBN1Mb4gqLwCg2slMEG4C9SK/IreydPLeJXu7 5a8AoOTYYIaq86Af9BRpmh/d91tz+RPp =/tM+ -----END PGP SIGNATURE----- --vb/P15UJLYd8hx0q--
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