Virtual Serial Port

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. :)

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.

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.

Mikado

Quoted 5 lines

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.

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.

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Quoted 8 lines

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

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?

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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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Quoted 4 lines

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?

Quoted 13 lines · Holy Aavu

Quoted 4 lines

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...

Quoted 1 line

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 <[email protected]>