Date: Sun, 7 Dec 2008 19:37:55 +0200 From: Kostik Belousov <kostikbel@gmail.com> To: Alexander Kabaev <kabaev@gmail.com> Cc: arch@freebsd.org, Joe Marcus Clarke <marcus@freebsd.org> Subject: Re: RFC: New VOP to translate vnode to its component name Message-ID: <20081207173755.GN2038@deviant.kiev.zoral.com.ua> In-Reply-To: <20081207114938.44255b35@kan.dnsalias.net> References: <1228667168.69753.16.camel@shumai.marcuscom.com> <20081207114938.44255b35@kan.dnsalias.net>
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--HJakWL7yBo69DI1O Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Sun, Dec 07, 2008 at 11:49:38AM -0500, Alexander Kabaev wrote: > On Sun, 07 Dec 2008 11:26:08 -0500 > Joe Marcus Clarke <marcus@FreeBSD.org> wrote: >=20 > > 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. In what sence its definition is bogus ? The vop should try to give a component name and a parent directory, if possible. It is perfectly acceptable to have several names, and return whatever is considered most suitable. Implementation may choose to always return a third element in some internal list, imagine any weird variant. Devfs implementation falls into this category. Or, it is possible to always return ENOENT, as is done in default implementation. I already discussed a possibility to add helper function that would do the usual readdir("..") to find vnode name for VDIR vnodes, with Peter Wemm. Using it as default implementation of vop_cnp should improve operation of vn_fullpath in general, and esp. on NFS. Personally for me, it would improve the accuracy of still alive patch that adds $ORIGIN support to rtld :). Please, state you objections more explicit. --HJakWL7yBo69DI1O Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (FreeBSD) iEYEARECAAYFAkk8CfIACgkQC3+MBN1Mb4iZOACePemsWP3N0kWWwW2cb1/DRrwn 3MAAnj7Ga53vCnDgfJWHGuGNbIPrii/G =Nv3E -----END PGP SIGNATURE----- --HJakWL7yBo69DI1O--
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