Date: Sun, 7 Dec 2008 11:49:38 -0500 From: Alexander Kabaev <kabaev@gmail.com> To: Joe Marcus Clarke <marcus@FreeBSD.org> Cc: arch@FreeBSD.org Subject: Re: RFC: New VOP to translate vnode to its component name Message-ID: <20081207114938.44255b35@kan.dnsalias.net> In-Reply-To: <1228667168.69753.16.camel@shumai.marcuscom.com> References: <1228667168.69753.16.camel@shumai.marcuscom.com>
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--Sig_/nSbrU2cOXEbEP1NwvOtBFEZ Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable On Sun, 07 Dec 2008 11:26:08 -0500 Joe Marcus Clarke <marcus@FreeBSD.org> wrote: > Background: >=20 > Procstat (i.e. kinfo_file) was a great addition which allows userland > processes to get a list of open files for a process without the need > for elevated privileges (e.g. kmem access). This feature uses the > VFS cache to find component names from vnodes in a process' file > descriptor table. Because of its ease of use, I quickly deployed it > into libgtop so that it could provide an lsof-like feature for > FreeBSD. >=20 > Another need arose that seemed perfect for procstat: the ability to > find out what process had the various mouse devices open. This was > needed for X.Org's HAL integration. Unfortunately, due to the fact > that devfs did not make use of the VFS cache, this was impossible to > do without bringing it a lot of kvm code from fstat, or simply > exec'ing fstat periodically. I chose the latter. The consequence is > easier-to-read code, but a performance hit with default HAL > configurations. >=20 > Robert Watson suggested I teach the VFS cache lookup function to query > file systems directly when cache lookups fail. After a few false > starts, and with the help of kib, I think I have a committable > implementation. >=20 > Solution: >=20 > Here is a patch to HEAD, along with a man page, for VOP_CNP. VOP_CNP > translates a vnode to its component name. It is currently called from > vn_fullpath1() to traverse a vnode hierarchy when cache lookups for > those vnodes fail. I have currently implemented VOP_CNP for devfs and > pseudofs. Kostik has thoroughly reviewed the devfs implementation. I > only recently did the pseudofs implementation at his request. > Additionally, the devfs implementation has gone through a Peter Holm > stress test, and survives (the pseudofs implementation survives > WITNESS and VFS lock debugging). >=20 > I would like to commit this work with a possible MFC to RELENG_7 to > come later. >=20 > http://www.marcuscom.com/downloads/vop_cnp_10.diff > http://www.marcuscom.com/downloads/VOP_CNP.9 >=20 > Joe >=20 In general, the relationship between vnode and componentnames is not 1:1, so I do not see how this VOP can possibly be made a permanent part of our VFS interface, as its definition is bogus by design. --=20 Alexander Kabaev --Sig_/nSbrU2cOXEbEP1NwvOtBFEZ Content-Type: application/pgp-signature; name=signature.asc Content-Disposition: attachment; filename=signature.asc -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (FreeBSD) iD8DBQFJO/6iQ6z1jMm+XZYRAtRPAKDVS/53jccwtSK6PYQMUANCEj7GKgCfbeax ui97ex4nvVwFwEYEWUdRlTo= =vDa0 -----END PGP SIGNATURE----- --Sig_/nSbrU2cOXEbEP1NwvOtBFEZ--
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