From owner-freebsd-hackers  Fri Jul 13 16:32:44 2001
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Date: Fri, 13 Jul 2001 19:32:31 -0400
From: Sergey Babkin <babkin@bellatlantic.net>
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To: Alfred Perlstein <bright@sneakerz.org>
Cc: Greg Lehey <grog@FreeBSD.org>, y-carden@uniandes.edu.co,
	FreeBSD Hackers <hackers@FreeBSD.org>
Subject: Re: Some questions about kernel programming
References: <M2001071206580901828@Ayax.uniandes.edu.co> <20010713113822.V45037@wantadilla.lemis.com> <20010712212809.F6664@sneakerz.org>
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Alfred Perlstein wrote:
> 
> * Greg Lehey <grog@FreeBSD.org> [010712 21:08] wrote:
> > On Thursday, 12 July 2001 at  6:58:09 -0500, y-carden@uniandes.edu.co wrote:
> > > Dear Friends
> > >
> > > I have some questions about kernel programming:
> >
> > You'd be better off sending mail like this to -hackers.  I've followed
> > up there.
> 
> I also got this in private mail, hrmm..
> 
> > write() doesn't exist in the kernel.  The simple answer is "you're
> > going to have to read what the send() syscall does and emulate it".
> > First, though, you need to answer the question "why do I want to do
> > this in the kernel?"
> 
> it actually exists, however the problem is that copyin and friends
> assume a seperate address space, I wonder if one could do some trick
> to alias the seperate address space on top of the kernel, that should
> allow copyin and friends to work on pointers into the kernel's address
> space.

Such as looking at dofilewrite() which is what write() calls
internally. dofilewrite() fills up a struct uio and calls the
file descriptor's filesystem-dependent write routine. The
difference for writing from kernel would be using UIO_SYSSPACE
instead of UIO_USERSPACE when preparing the uio structure.

-SB

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