Date: Wed, 16 Apr 2008 10:03:42 -0700 From: Alfred Perlstein <alfred@freebsd.org> To: Pawel Jakub Dawidek <pjd@FreeBSD.org> Cc: rwatson@freebsd.org, Roman Divacky <rdivacky@freebsd.org>, kib@freebsd.org, freebsd-arch@freebsd.org Subject: Re: final decision about *at syscalls Message-ID: <20080416170341.GN95731@elvis.mu.org> In-Reply-To: <20080416165612.GA31094@garage.freebsd.pl> References: <20071218092222.GA9695@freebsd.org> <200712201138.56423.jhb@freebsd.org> <20080412112019.GI45299@garage.freebsd.pl> <200804161014.41025.jhb@freebsd.org> <20080416165612.GA31094@garage.freebsd.pl>
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* Pawel Jakub Dawidek <pjd@FreeBSD.org> [080416 09:56] wrote: > On Wed, Apr 16, 2008 at 10:14:40AM -0400, John Baldwin wrote: > > On Saturday 12 April 2008 07:20:19 am Pawel Jakub Dawidek wrote: > > > From what you write John, #1 is a better choice than #2. If you want to > > > avoid races, you can pass already locked vnode. In case of file > > > descriptors, if p_fd is not locked another thread can close and open > > > different directory under the same descriptor number. > > > > Did you read Robert's paper? Do you not realize that the kernel copying data > > in from userland multiple times and having it change in between is very bug > > prone? > > Believe me I'm fully aware of the problems Robert described in his > paper. With vnode approach where do you have more data copying between > kernel and userland? > > File descriptor proposal works like this: > > userland > openat(fd, path) > kernel > NDINIT_AT(&vp, path, fd); > /* operate on vp */ > > Vnode proposal works this way: > > userland > openat(fd, path) > kernel > dvp = file_descriptor_to_vnode(fd); > NDINIT_AT(&vp, path, dvp); > /* operate on vp */ My first impression is that passing fp to vp code is a layering violation and bad news. I need to think about it more. -- - Alfred Perlstein
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