On Fri, Oct 4, 2019 at 2:12 PM John Baldwin <j...@freebsd.org> wrote: > > On 10/4/19 6:43 AM, Kyle Evans wrote: > > Author: kevans > > Date: Fri Oct 4 13:43:07 2019 > > New Revision: 353103 > > URL: https://svnweb.freebsd.org/changeset/base/353103 > > > > Log: > > tuntap(4): loosen up tunclose restrictions > > > > Realistically, this cannot work. We don't allow the tun to be opened > > twice, > > so it must be done via fd passing, fork, dup, some mechanism like these. > > Applications demonstrably do not enforce strict ordering when they're > > handing off tun devices, so the parent closing before the child will > > easily > > leave the tun/tap device in a bad state where it can't be destroyed and a > > confused user because they did nothing wrong. > > > > Concede that we can't leave the tun/tap device in this kind of state > > because > > of software not playing the TUNSIFPID game, but it is still good to find > > and > > fix this kind of thing to keep ifconfig(8) up-to-date and help ensure good > > discipline in tun handling. > > Why are you using d_close for last close anyway? It's not really reliable > compared > to using cdevpriv and a cdevpriv dtor. >
This decision predates me by a long time, I'm afraid. =-) If you have time to elaborate on the comparable reliability point, I'd be interested in hearing it. A little bit of searching didn't seem to turn up much there, I'm afraid. I did otherwise spend a little bit of time diving into the path taken to get to d_close and the trade-offs between cdevpriv vs. what tuntap does now. I think I'm convinced either way that cdevpriv is a good way to go- it seems to have the advantage that with a little refactoring we could actually set the softc atomically on the device cdevpriv instead of cdev->si_drv1 and I can axe this rwatson@ comment about the non-atomic test and set. I don't see any downside here. _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
