Date: Mon, 25 Jul 2005 15:18:44 +0200 From: "Norbert Koch" <NKoch@demig.de> To: <Felix-KM@yandex.ru>, <freebsd-hackers@freebsd.org> Subject: RE: how to use the function copyout() Message-ID: <000101c5911b$62441260$4801a8c0@ws-ew-3.W2KDEMIG> In-Reply-To: <42E4DC88.000006.21996@camay.yandex.ru>
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> #define IOCTL_GET_B _IOWR("F", 127, 0x4)
I think the third parameter to _IOWR should directly specify a type,
e.g. _IOWR("F", 127, int) or _IOWR("F", 127, struct MyStruct).
>
> ---- driver ----
>
> struct my_softc {
> ...
> short unsigned int B;
> };
>
> ...
>
> static int
> my_ioctl(struct cdev *dev, u_long cmd, caddr_t data, int flag,
> struct thread *td)
> {
> struct my_softc *my_sc;
> int unit, error;
> unit = minor(dev);
> my_sc = (struct my_softc *)devclass_get_softc(my_devclass, unit);
> if (my_sc == NULL)
> return (ENXIO);
> switch(cmd)
> {
> ...
> case IOCTL_GET_B:
> error = copyout(&my_sc->B, data, sizeof(my_sc->B));
> switch (error)
> {
> case 0:
> printf(" IOCTL_GET_B: %d\n", my_sc->B);
> break;
> case EFAULT:
> printf("EFAULT\n");
> break;
> case EIO:
> printf("EIO\n");
> break;
> case ENOMEM:
> printf("ENOMEM\n");
> break;
> case ENOSPC:
> printf("ENOSPC\n");
> break;
> }
> break;
> default:
> break;
> }
> return 0;
> }
>
> ---user program ----------------------
>
> ...
>
> short unsigned int Data[32768];
>
> int
> main(int argc, char *argv[])
> { ...
>
> if (ioctl(fd0, IOCTL_GET_B, Data) == -1)
> err(1, "IOCTL_GET_B");
>
> ...
> }
>
> -------
>
> Here I get EFAULT.
>
> What have I done wrong? How can I do it correctly?
The caddr_t data in your ioctl is already mapped into kernel
memory. Look into the source of other device drivers. You'll
find a lot of *(int *) data = ...
So your copyout() has to fail because it tries to address
memory which is not a part of your application's
memory.
>From errno(2): EFAULT: Bad address...
I have no idea if it is possible for ioctls to have mapped more
than a few 100 bytes for data exchange.
You should use read and uiomove() instead.
Norbert
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