Date: Wed, 03 Sep 1997 19:35:42 -0700 (PDT) From: Simon Shapiro <Shimon@i-Connect.Net> To: Mike Smith <mike@smith.net.au> Cc: freebsd-hackers@freebsd.org Subject: Re: IOCTL Commands - Where is my mistake? Message-ID: <XFMail.970903193542.Shimon@i-Connect.Net> In-Reply-To: <199709040209.LAA00716@word.smith.net.au>
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Hi Mike Smith; On 04-Sep-97 you wrote:
> > Thax for the help Mike!
> >
> > Hi Mike Smith; On 03-Sep-97 you wrote:
> > > > I want to pass IOCTL commands to a driver. This is what I do:
> > > >
> > > > #define DPT_IOCTL_INTERNAL_METRICS _IOW('D', 1,
> > > > #dpt_perf_t)
> > >
> > > You want to pass a pointer to the struct, not the struct itself.
> >
> > I do. what gave you the idea I do not?
>
> dpt_perf_t is common lingo for a structure definition. If you mean
> that it is a pointer, then you should not be calling it that.
I almost agree. It is a common syntax for user defined data types, as in
u_int8_t (which is not a structure, last I checked :-)
Now, as you point below, the _IO{R,W,WR) macros, use the thrid argument
as the argument of sizeof. Last I checked, given ``int x;'', sizeof(int)
and sizeof(x) are the same. But given my limited knwoledge in this
matters, I must be mistaken. Just to try and prove you right, I tried
both ways.
>
> > > > switch (cmd) {
> > > > case DPT_IOCTL_INTERNAL_METRICS:
> > > > result = copyout((char *)&dpt->performance,
> > > > (dpt_softc_t *)(*(caddr_t *)cmdarg),
> > > > sizeof(dpt_perf_t));
> > >
> > > This is *hideously* bogus. Try :
> > >
> > > caddr_t dest;
> > >
> > > /* get address in userspace */
> > > dest = fuword(*(caddr_t *)cmdarg);
> >
> > This is *hideously* not portable :-) You assume an integer and a char
> > *
> > are the same. Should be dest = (caddr_t)fuword....
>
> Given that I am also assuming that a userspace pointer fits in a
> "word", the extra cast didn't seem worth the effort. If/when fuaddr()
> comes into the picture, I'll start using it.
This assumption is just that; Assumption. In my days, we did NOT assume
anything about data types and what fits where. In any case, this is not
where my mistake is.
> > I did. I am still getting the SAME result. Maybe I should re-state
> > that:
> >
> > If I do:
> >
> > #define DPT_IOCTL_INTERNAL_METRICS _IOR('D', 1, dpt_perf_t)
> >
> > Then copyout fails!
>
> Have you bothered to print the address that you are trying to copy out
> to?
>
> > BUT if I do:
> >
> > #define DPT_IOCTL_INTERNAL_METRICS (IOC_INOUT | 1)
> >
> > Then it WORKS.
>
> So what? You're the benficiary of a fencepost error in that you
> shouldn't be getting anything copied in or out at all. Look at the
> definition of the _IO* macros :
>
> #define _IOC(inout,group,num,len) \
> (inout | ((len & IOCPARM_MASK) << 16) | ((group) << 8) | (num))
> #define _IO(g,n) _IOC(IOC_VOID, (g), (n), 0)
> #define _IOR(g,n,t) _IOC(IOC_OUT, (g), (n), sizeof(t))
> #define _IOW(g,n,t) _IOC(IOC_IN, (g), (n), sizeof(t))
> /* this should be _IORW, but stdio got there first */
> #define _IOWR(g,n,t) _IOC(IOC_INOUT, (g), (n), sizeof(t))
I read those. I still fail to see where I erred. Please nderstand, I
made a mistake. Foolish one, no doubt. But what?
>
> > The fact that the contents of cmd (NOT the identity of cmdarg!) changes
> > the outcome of copyout, coupled with the fact that your version,
> > although
> > not nearly as *hideously* bogus as mine, does NOT work, coupled to the
> > fact that ioctl does work, leads me to belive that I am making a stupid
> > mistake, but your solution is not indicating my error.
>
> I have, indeed, indicated your error. The object supplied as an
> argument to the ioctl is copied to/from kernel space dependant on the
> _IO macro flavour. The *address* of this copied object is passed to
> your ioctl handler in (cmdarg). You can either pass a user-space
> address in, and use this address as the argument to a copyout, or you
> can request that the entire structure be copied out and supply an
> entire structure.
I tried both ways. It does not work. Thanx for the attempt...
---
Sincerely Yours, (Sent on 03-Sep-97, 19:25:24 by XF-Mail)
Simon Shapiro Atlas Telecom
Senior Architect 14355 SW Allen Blvd., Suite 130 Beaverton OR
97005
Shimon@i-Connect.Net Voice: 503.643.5559, Emergency: 503.799.2313
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