Virtual Serial Port

Virtual Serial Port

[Mikado]

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My machine has only one serial port. Now I want to add more *software*
(virtual) serial ports. I also want to make a virtual serial cable
between a real serial port and a virtual one OR between virtual ports.
Is there any way to solve that problem in our universe?

Thanks,
Mikado.
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Re: Virtual Serial Port

[Jan Engelhardt]

>My machine has only one serial port. Now I want to add more *software*
>(virtual) serial ports. I also want to make a virtual serial cable
>between a real serial port and a virtual one OR between virtual ports.
>Is there any way to solve that problem in our universe?

You could write a device driver implementing virtual serial ports. Then you 
just add an ioctl that connects/disconnects virtual ports to real ports if 
desired.
I do not quite see what this would be good for, but I am sure it's 
good for learning or for fun. :)



Jan Engelhardt
-- 

Re: Virtual Serial Port

[Mikado]

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> You could write a device driver implementing virtual serial ports. Then you 
> just add an ioctl that connects/disconnects virtual ports to real ports if 
> desired.
> I do not quite see what this would be good for, but I am sure it's 
> good for learning or for fun. :)

Hi Jan Engelhardt,

My purpose is to provide serial interfaces for debugging. My real box
acts as remote host connecting to VMWare box by a *virtual* serial cable
so that I can set up a debugging environment.

There are several solutions for this problem but they could only run on
Windows. Eg:
- - http://www.mks.zp.ua/vspdxp.php
- - http://www.virtual-serial-port.com/virtual-serial-port-kit.html

I'll buy an USB-to-Serial cable and a Serial-Serial cable to solve this
problem but it's also interesting for me to write such device driver.
I'll try it later.

Mikado
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Re: Virtual Serial Port

[Anderson Lizardo]

On 3/25/06, Mikado <mikado4vn@gmail.com> wrote:
> My purpose is to provide serial interfaces for debugging. My real box
> acts as remote host connecting to VMWare box by a *virtual* serial cable
> so that I can set up a debugging environment.

Have you tried using software-based serial snoopers? See e.g.
http://freshmeat.net/snooper and
http://packages.debian.org/unstable/comm/snooper. Haven't tried any of
these but they seem to do what you describe.

Regards,
--
Anderson Lizardo
Embedded Linux Lab - 10LE
Nokia Institute of Technology - INdT
Manaus - Brazil

Re: Virtual Serial Port

[Jan Engelhardt]

>> You could write a device driver implementing virtual serial ports. Then you 
>> just add an ioctl that connects/disconnects virtual ports to real ports if 
>> desired.
>> I do not quite see what this would be good for, but I am sure it's 
>> good for learning or for fun. :)
>
>My purpose is to provide serial interfaces for debugging. My real box
>acts as remote host connecting to VMWare box by a *virtual* serial cable
>so that I can set up a debugging environment.
>
Ah! You don't want to have the X11 overhead of VMware. Quite an idea.
If I get it right, your setup looks like:

  guest writes to /dev/ttyS0
  vmware connects its virtual S0 to the host's ttyFakeS0
  minicom on the host to ttyFakeS0
or even
  vmware S0 to host's ttyS0
  other remote machine do minicom to ttyS0

The reason for FakeS0 is that vmware does not know about ptys, 
unfortunately.


Jan Engelhardt
-- 

Re: Virtual Serial Port

[Mikado]

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>   guest writes to /dev/ttyS0
>   vmware connects its virtual S0 to the host's ttyFakeS0
>   minicom on the host to ttyFakeS0
> or even
>   vmware S0 to host's ttyS0
>   other remote machine do minicom to ttyS0
> 
> The reason for FakeS0 is that vmware does not know about ptys, 
> unfortunately.

Yes, VMWare doesn't support serial port using host's ttys any more. My
idea is:

[host - application] <- read/write -> [virtual serial port
/dev/ttyFakeS0] <- read/write over virtual null-modem serial cable ->
[host - real serial port /dev/ttyS0] <- read/write -> [VMWare - application]

But today I've just bought an USB-to-Serial converter and made for
myself a null-modem serial cable. I use this null-modem cable to connect
/dev/ttyS0 (native serial port) to /dev/tts/USB0 (USB-based serial
port). My VMWare now can use one of those devices and the host use
another one. Now above figure can be re-drawn like this:

[host - application] <- read/write -> [/dev/tts/USB0] <- read/write over
physical null-modem cable -> [/dev/ttyS0] <- read/write -> [VMWare -
application]

Anyway, later I'll try to write a device drivers act as virtual serial
ports and virtual null-modem cables.

Best regards,
Mikado.
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Re: Virtual Serial Port

[Petr Vandrovec]

Mikado wrote:
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> 
> 
>>  guest writes to /dev/ttyS0
>>  vmware connects its virtual S0 to the host's ttyFakeS0
>>  minicom on the host to ttyFakeS0
>>or even
>>  vmware S0 to host's ttyS0
>>  other remote machine do minicom to ttyS0
>>
>>The reason for FakeS0 is that vmware does not know about ptys, 
>>unfortunately.
> 
> 
> Yes, VMWare doesn't support serial port using host's ttys any more. My
> idea is:
> 
> [host - application] <- read/write -> [virtual serial port
> /dev/ttyFakeS0] <- read/write over virtual null-modem serial cable ->
> [host - real serial port /dev/ttyS0] <- read/write -> [VMWare - application]

Although it is quite irrelevant to LKML (you may want to visit 
www.vmware.com/community/index.jspa and ask there...), you can connect guest's 
serial port also to Unix socket - and in such situation you need virtual serial 
port driver only if 'host - application' does not know how to use /dev/tty* (for 
unix socket <-> /dev/ptyp* app look at 
http://platan.vc.cvut.cz/ftp/pub/vmware/serpipe.tar.gz).
								Petr

Re: Virtual Serial Port

[Mikado]

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Petr Vandrovec wrote:
> Although it is quite irrelevant to LKML (you may want to visit
> www.vmware.com/community/index.jspa and ask there...), you can connect
> guest's serial port also to Unix socket - and in such situation you need
> virtual serial port driver only if 'host - application' does not know
> how to use /dev/tty* (for unix socket <-> /dev/ptyp* app look at
> http://platan.vc.cvut.cz/ftp/pub/vmware/serpipe.tar.gz).
>                                 Petr


Thank Petr. It also works well. That program acts as a data proxy
between unix socket and /dev/ptyp*. Yesterday I wrote a similar program
that read/write vmware's server unix sock then forward/backward data
to/from /dev/ptyp0 but it didn't work. Maybe my program has problem.
Thanks again.

Mikado
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Re: Virtual Serial Port

[Glynn Clements]

Mikado wrote:

> My machine has only one serial port. Now I want to add more *software*
> (virtual) serial ports. I also want to make a virtual serial cable
> between a real serial port and a virtual one OR between virtual ports.
> Is there any way to solve that problem in our universe?

Will a pty suffice?

-- 
Glynn Clements <glynn@gclements.plus.com>

Re: Virtual Serial Port

[Holy Aavu]

On 3/25/06, Mikado <mikado4vn@gmail.com> wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> My machine has only one serial port. Now I want to add more *software*
> (virtual) serial ports. I also want to make a virtual serial cable
> between a real serial port and a virtual one OR between virtual ports.
> Is there any way to solve that problem in our universe?

I have a doubt... I am not sure if you can have a full working
solution to make all programs run using the virtual serial ports.
Because, there *might* be some programs which actually use the 'in'
and 'out' instructions of the processor directly from a user space
program. (After calling iopl/ioperm etc to elevate their I/O
privileges to directly use the IO ports) I dont think even a kernel
change can help in that case...

Is my understanding correct or am I missing something?

>
> Thanks,
> Mikado.
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Re: Virtual Serial Port

[Glynn Clements]

Holy Aavu wrote:

> > My machine has only one serial port. Now I want to add more *software*
> > (virtual) serial ports. I also want to make a virtual serial cable
> > between a real serial port and a virtual one OR between virtual ports.
> > Is there any way to solve that problem in our universe?
> 
> I have a doubt... I am not sure if you can have a full working
> solution to make all programs run using the virtual serial ports.
> Because, there *might* be some programs which actually use the 'in'
> and 'out' instructions of the processor directly from a user space
> program. (After calling iopl/ioperm etc to elevate their I/O
> privileges to directly use the IO ports) I dont think even a kernel
> change can help in that case...
> 
> Is my understanding correct or am I missing something?

1. Any such programs will only work with "PC-style" serial ports (8250
and compatible UARTs); they won't work with other serial hardware
(e.g. multi-port serial cards). Also, such programs would require root
privilege. Consequently, most programs which use serial ports limit
themselves to using the /dev/tty* devices and their associated ioctl()
calls.

2. You could change the iopl() system call so that it doesn't affect
the IOPL bits in the EFLAGS register. Instead, you would handle the
resulting exceptions, trapping attempts to access the UARTs and
redirecting them to the "virtual UART" driver. The ioperm() system
call would need similar modifications.

-- 
Glynn Clements <glynn@gclements.plus.com>

Re: Virtual Serial Port

[Holy Aavu]

On 3/27/06, Glynn Clements <glynn@gclements.plus.com> wrote:
>
> Holy Aavu wrote:
>
> > > My machine has only one serial port. Now I want to add more *software*
> > > (virtual) serial ports. I also want to make a virtual serial cable
> > > between a real serial port and a virtual one OR between virtual ports.
> > > Is there any way to solve that problem in our universe?
> >
> > I have a doubt... I am not sure if you can have a full working
> > solution to make all programs run using the virtual serial ports.
> > Because, there *might* be some programs which actually use the 'in'
> > and 'out' instructions of the processor directly from a user space
> > program. (After calling iopl/ioperm etc to elevate their I/O
> > privileges to directly use the IO ports) I dont think even a kernel
> > change can help in that case...
> >
> > Is my understanding correct or am I missing something?
>
> 1. Any such programs will only work with "PC-style" serial ports (8250
> and compatible UARTs); they won't work with other serial hardware
> (e.g. multi-port serial cards). Also, such programs would require root
> privilege. Consequently, most programs which use serial ports limit
> themselves to using the /dev/tty* devices and their associated ioctl()
> calls.
>
> 2. You could change the iopl() system call so that it doesn't affect
> the IOPL bits in the EFLAGS register. Instead, you would handle the
> resulting exceptions, trapping attempts to access the UARTs and
> redirecting them to the "virtual UART" driver. The ioperm() system
> call would need similar modifications.
>

Thanks Glynn, that explains a lot!

> --
> Glynn Clements <glynn@gclements.plus.com>
>