Date: Tue, 29 Jul 1997 19:27:30 -0700 (PDT) From: Vinay Bannai <vinay@agni.nuko.com> To: dg@root.com Cc: terry@lambert.org, freebsd-hackers@FreeBSD.ORG Subject: Re: Location of copyin() and copyout().. Message-ID: <199707300227.TAA05696@agni.nuko.com> In-Reply-To: <199707300146.SAA11272@implode.root.com> from "David Greenman" at "Jul 29, 97 06:46:08 pm"
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According to David Greenman: > >> It is generally considered _extremely_ bad to use copyin/copyout, as it > >> precludes your functions from being called from within kernel space. > >> > >> FWIW, this is what eventually stumped me when it came to getting Linux > >> WABI running on FreeBSD. > > > >This is a good point, considering that kernel preemption is one > >of my own goals. > > > >The issue is recursion with a paging operation in progress. > > > >I think with the limited cases I gave (the page is filled, the > >call made, and the page is still mapped) are OK. > > > >copying out is more likely to cause problems than copying in, > >since you copy in pages after they are touched, but you potentially > >touch on copyout. > > > >Probably there needs to be _copyin/_copyout for the internal usage, > >and a "safe" copyin/copyout for usage which isn't safed against > >reentrancy. > > There is no problem with using copyout() in the kernel to copy data out to > a user process, assuming that the currently running process is the intended > target of the copy. That is the sole purpose of the function. copyout() > correctly handles all issues of COW/ZF/page faults. > uiomove() is escentially a wrapper for copyin/copyout that has an > optimization for the case of kernel-to-kernel copies (in which case it > uses bcopy instead). > > -DG So in a situation where I pin the user pages down (for DMA), it is okay to use copyin()/copyout(). In the meantime, I am having a little trouble with the code that is running on the i960 board. It is essentially probed/attached/mmapped from the host side. It mostly pertains to style and structure on the code that is running on the i960 board. The card offers a broad functionality (depending on the code running on the board). How do I offer these services thru the device driver end on the host side? For instance I can't seem to map the functiions provided by the i960 processor onto the ioctl(). I am ignoring the I2O model for the time being. I want to be able to get the initial prototype atleast working before I touch the I20 specs... Suggestions and words of wisdom gladly accepted... Vinay -- Vinay Bannai E-mail: vinay@agni.nuko.com (408)-526-0280 x 275 (Work) http://agni.nuko.com/~vinay
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