Re: wrong number of serial port detected

Jason Dravet
2005-12-08T03:02:05Z

>From: Russell King <rmk+lkml@arm.linux.org.uk>
>To: Jason Dravet <dravet@hotmail.com>
>CC: linux-kernel@vger.kernel.org
>Subject: Re: wrong number of serial port detected
>Date: Wed, 7 Dec 2005 21:15:51 +0000
>
>On Wed, Dec 07, 2005 at 01:59:43PM -0600, Jason Dravet wrote:
> > >From: Russell King <rmk+lkml@arm.linux.org.uk>
> > >To: Jason Dravet <dravet@hotmail.com>
> > >CC: linux-kernel@vger.kernel.org
> > >Subject: Re: wrong number of serial port detected
> > >Date: Wed, 7 Dec 2005 15:50:34 +0000
> > >
> > >On Wed, Dec 07, 2005 at 09:44:29AM -0600, Jason Dravet wrote:
> > >> So I ask this mailing list Can the kernel detect the proper number of
> > >> serial ports or not?
> > >
> > >It does detect serial ports found in the machine.
> > >
> > >However, it _always_ offers the configured number of serial devices.
> > >This is to allow folk whose ports are not autodetected to configure
> > >them appropriately via the setserial command. If they were not
> > >available, they could not configure them.
> > >
> > Then may I ask how XP does it? I have to dual boot between XP and
>Fedora.
> > When I go into XP's device manager I see all of the appropriate hardware
> > listed, no extra serial ports. When I boot into Fedora and go into
>/dev, I
> > see the same hardware except I have 32 serial ports and 64 tty nodes
>(tty
> > is for virtual terminals right?). How can 1 OS show the correct number
>and
> > another show the wrong number? I ask so I can better understand what is
> > going on.
>
>It seems you are comparing apples (XP's device manager) with oranges
>(/dev directory). They're two entirely different things.
>
>The former lists devices which _are_ present in your system.
>
>The latter provides the filesystem namespace for applications to access
>devices which may or may not be present in your system.
>
I thought the purpose of udev was to create device manager like
functionality. I posted my question here because udev is creating 32 nodes.
Udev gets that information from the kernel serial port driver. Thanks to
your explanation I now understand. This is why I ask questions so I can
learn.

>As for your 64 VT tty device nodes - these "devices" are created
>dynamically when the device node is opened. The act of opening the
>device node is defined to be the creation event. If the device node
>did not exist, there would be no way to create _any_ virtual terminals.
>
I thought there were only 7 tty devices (Ctrl-F1 to Ctrl-F7) for local
system login? Ctrl-F7 being for Xwindows. Did I miss something?

Thank you for taking the time to answer my questions. I really appreciate
it.
Jason