final decision about *at syscalls

[Pawel Jakub Dawidek]

On Thu, Apr 17, 2008 at 09:33:45AM -0400, John Baldwin wrote:
> 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

Ah, ok. I don't think this is not method's flaw, but implementation
problem.

-- 
Pawel Jakub Dawidek                       http://www.wheel.pl
pjd at FreeBSD.org                           http://www.FreeBSD.org
FreeBSD committer                         Am I Evil? Yes, I Am!
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