Date: Thu, 15 Nov 2001 09:06:20 -0500 (EST) From: Robert Watson <rwatson@FreeBSD.ORG> To: Matthew Dillon <dillon@apollo.backplane.com> Cc: Alfred Perlstein <bright@mu.org>, Greg Lehey <grog@FreeBSD.ORG>, Bruce Evans <bde@zeta.org.au>, Peter Wemm <peter@wemm.org>, freebsd-arch@FreeBSD.ORG Subject: Re: cur{thread/proc}, or not. Message-ID: <Pine.NEB.3.96L.1011115090027.87678A-100000@fledge.watson.org> In-Reply-To: <200111150518.fAF5IMW18730@apollo.backplane.com>
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On Wed, 14 Nov 2001, Matthew Dillon wrote: > > :If you want to see why curproc sucks then please investigate what > :happens when you NDINIT a nameidata with another thread pointer > :other than your own, then perform a vn_open. kablooey! > : > :My recent addition of vn_open_cred and modification of nfs_lock.c > :was to get around this badness of the API. > : > :-- > :-Alfred Perlstein [alfred@freebsd.org] > > I'm not sure this is a fair argument. Just about all the code > in the system taking a struct thread * pointer assumes that the > thread is the current thread and so avoid much of the locking that > they would normally have to do on it. Passing some other thread > to a good chunk of this code will have very weird broken results. In my mind, that is in fact the primary argument *to* use curproc instead of passing around process and thread pointers. If the routine implicitly assumes curproc or curthread for locking/referencing purposes, either there needs to be a way to assert that: int foobar(struct thread *td, int arg) { PROMISE_ME_ITS_CURTHREAD_OR_DIE_HORRIBLY(td); arg += td->td_only_safe_to_read_without_lock_if_curthread; /* * Contrived example a little less contrived: * return (td->td_ucred->cr_uid == arg); */ return (arg); } or, we simply need to use curthread and curproc, and not allow anything else to be passed in. int foobar(int arg) { arg += curthread->td_only_safe_to_read_without_lock_if_curthread; return (arg); } Robert N M Watson FreeBSD Core Team, TrustedBSD Project robert@fledge.watson.org NAI Labs, Safeport Network Services To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
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