Date: Sun, 22 Aug 2004 00:18:20 -0700 From: John-Mark Gurney <gurney_j@resnet.uoregon.edu> To: Alfred Perlstein <alfred@freebsd.org> Cc: hackers@freebsd.org Subject: Re: sysctl hacks Message-ID: <20040822071820.GA29902@funkthat.com> In-Reply-To: <20040822064707.GF26612@elvis.mu.org> References: <20040821200205.GE26612@elvis.mu.org> <46719.1093120181@critter.freebsd.dk> <20040822064707.GF26612@elvis.mu.org>
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Alfred Perlstein wrote this message on Sat, Aug 21, 2004 at 23:47 -0700:
> * Poul-Henning Kamp <phk@phk.freebsd.dk> [040821 13:29] wrote:
> > In message <20040821200205.GE26612@elvis.mu.org>, Alfred Perlstein writes:
> > >I'm doing some work that requires that I have a sysctl structure
> > >be passed around, but inside that structure are several pointers I
> > >may need to dereference.
> > >
> > >Basically:
> > >
> > >struct mysysctldata {
> > > .... (data here)
> > > void *moredata;
> > > size_t morelen;
> > >};
> > >
> > >What is the proper way of sysctl'ing IN the data from moredata?
> > >
> > >I need to make a copy of the sysctl req, but... I'm not sure what
> > >to initialize the 'lock' member to.
> >
> > Just use the SYSCTL_IN() and ..._OUT() functions.
>
> :(
>
> I wasn't clear.
>
> 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.
--
John-Mark Gurney Voice: +1 415 225 5579
"All that I will do, has been done, All that I have, has not."
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