Date: Fri, 21 Mar 2003 15:22:43 -0800 From: Terry Lambert <tlambert2@mindspring.com> To: Poul-Henning Kamp <phk@phk.freebsd.dk> Cc: arch@freebsd.org Subject: Re: GEOM ioctl issue. Message-ID: <3E7B9EC3.212B866@mindspring.com> References: <11639.1048286747@critter.freebsd.dk>
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Poul-Henning Kamp wrote: > If the primary argument is a struct containing pointer(s) to something > else, a string or maybe another structure, these secondary arguments > are not handled in the generic ioctl syscall code, it becomes the > responsibility of the ioctl implementor to explicity call > copyin(9)/copyout(9) on these arguments. > > The way we have implemented copyin(9) and copyout(9) depends strongly > on the fact that they are executed in the corresponding thread, it is > not possible to access userland for one thread with copyin/out from > another thread, userland or kernel. > > GEOM abandons the original thread as the very first thing, there > are a multitude of reasons for this, the primary being prevention > of kernel stack overrun and the second realible and simple serialization. Go ahead and abandon the thread, but before you do, allocate a glue structure that contains: pointer to first argument pointer to thread to be abandoned Then, when you need it, you can recover the thread context to do the copyin/copyout, as necessary. If you are willing to reduce the overall size that you allow for the data, then you can "steal" it up front. You probably don't need this, because it's not like it's performance critical to not allocated and deallocate a glue structure. Otherwise, you could halve the size, and take a bit to mean "do not do early abandonment of the thread". That's probably overkill. -- Terry To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
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