Date: Thu, 17 Apr 2008 09:33:45 -0400 From: John Baldwin <jhb@freebsd.org> To: Pawel Jakub Dawidek <pjd@freebsd.org> Cc: kib@freebsd.org, Roman Divacky <rdivacky@freebsd.org>, rwatson@freebsd.org, freebsd-arch@freebsd.org Subject: Re: final decision about *at syscalls Message-ID: <200804170933.45477.jhb@freebsd.org> In-Reply-To: <20080416165612.GA31094@garage.freebsd.pl> References: <20071218092222.GA9695@freebsd.org> <200804161014.41025.jhb@freebsd.org> <20080416165612.GA31094@garage.freebsd.pl>
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On Wednesday 16 April 2008 12:56:12 pm Pawel Jakub Dawidek 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? Only because it was explicitly mentioned in the original e-mail: > CONs of #1 > > o some very small code duplication (the translation is done in every > kern_fooat() function) > o there is a race between the name translation and the actual use of the result > of the translation that needs to be handled, the "path_to_file" string is copied > to the kernel space twice hence a race -- John Baldwin
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