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Date: Sun, 22 Aug 2004 00:28:47 -0700
From: Alfred Perlstein <alfred@freebsd.org>
To: Poul-Henning Kamp <phk@phk.freebsd.dk>, hackers@freebsd.org
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Subject: Re: sysctl hacks
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* John-Mark Gurney <gurney_j@resnet.uoregon.edu> [040822 00:18] wrote:
> Alfred Perlstein wrote this message on Sat, Aug 21, 2004 at 23:47 -0700:
> > 
> > I have a sysctl node that takes a struct like so:
> > 
> > struct mysysctldata {
> >   .... (data here)
> >   struct moredata * vc_ptr;
> >   size_t len vc_len;
> > }
> > 
> > If I use SYSCTL_IN(), then I can get "mysysctldata", but I only
> > get the pointer to "moredata", now I want to get a copy of 
> > "moredata", what's a good way to do this?
> > 
> > I have a macro that does this:
> > 
> > #define VCTLTOREQ(vc, req)						\
> > 	do {								\
> > 		(req)->newptr = (vc)->vc_ptr;				\
> > 		(req)->newlen = (vc)->vc_len;				\
> > 		(req)->newidx = 0;					\
> > 	} while (0)
> > 
> > Is that right?
> 
> After reading the sysctl code, it appears that you can't do that..
> SYSCTL_IN only lets you read serially from the buffer passed in...  so
> you have to have all the data serially in userland...  once you do a
> SYSCTL_IN of x bytes of data, the pointer is updated to skip those x,
> and the next call will read in the bytes following the first read...
> 
> Hope this helps.

Yes, but you can update the sysctlreq struct's newptr, newlen and
newidx to point to the auxiliary data as my macro does, I just
wanted to make sure I wasn't missing some subtle point of the
how sysctl works.

-- 
- Alfred Perlstein
- Research Engineering Development Inc.
- email: bright@mu.org cell: 408-480-4684