Subject: Re: should cngetc block?
To: Kin Cho <firstname.lastname@example.org>
From: Bill Studenmund <email@example.com>
Date: 02/08/2002 12:06:11
On 8 Feb 2002, Kin Cho wrote:
> Bill Studenmund <firstname.lastname@example.org> writes:
> > cnopen(<console dev for your port>, FREAD | FWRITE | <other opts>
> > 0, curproc);
> What can I use for <console dev for your port>? I tried using
> cn_tab->cn_dev but that's forbidden in cnopen because cn_dev is
> alrady set to our "com0" device in com_attach_subr in
> cn_tab->cn_dev = makedev(maj, sc->sc_dev.dv_unit);
ls -l /dev/console
For i386, it's major 0, minor 0. So "0" is the right value.
> > /*
> > * Set up a uio to do a read, then call cnread()
> > */
> I have no experience with uio. Searching around, here's what I
> come up with:
> struct iovec aiov;
> struct uio auio;
> int buf; // code and lsr as stored in comintr?
> aiov.iov_base = buf;
> aiov.iov_len = sizeof(buf);
> auio.uio_iov = &aiov;
> auio.uio_iovcnt = 1;
> auio.uio_offset = 0;
> auio.uio_resid = 0;
> auio.uio_segflg = UIO_SYSSPACE;
> auio.uio_rw = UIO_READ;
> auio.uio_procp = curproc;
> ret = cnread(<dev>, &auio, 0);
> I doubt that iov_len, uio_offset, and uio_resid are right.
> Any suggestion what they should be?
man read tells some.
uio_offset is fine, as you're reading a device that can't seek. uio_resid
is how much is left to do, 0 is a good initial value.
iov_len is the length of the memory area pointed to by iov_base. i.e. the
size of the buffer.
Note that you will be reading characters just like a userland process
would. So the standard tty processing will have happened.