Named Pipe Serial Port
Connecting to Virtual Serial Port using Putty. Over on VMware Forums back in 2004 someone posted that to connect to serial named pipes, they just type in the pipe name as the serial port. So i went about trying to figure out how to configure that in VirtualBox and it worked, so now i’ll share with you my configuration. In Hyper-V on the XP guest I edited the COM1 Serial Port setting by selecting Named Pipe and in the pipe name field entered COM3 this caused the Named pipe path: field to display.pipeCOM3. I then connected the serial cable to the port ran Putty on the guest as.
'Each virtual machine is configured with 2 virtual serial (COM) ports that can be attached to a named pipe to communicate with a local or remote physical computer. To connect a virtual serial device to the named pipe, use IVirtualSerialDevice.connectToPipe method to connect to existing pipe (client mode) or IVirtualSerialDevice.createAndConnectPipe method to create a named pipe and connect to it in server mode. When an application writes data to the serial port, all written data is transferred. The Set-VMComPort cmdlet configures the COM port of a virtual machine. PS C: Set-VMComPort TestVM 2. Pipe TestPipe. Configure the second COM port on virtual machine TestVM to connect to named pipe TestPipe on the local computer.
Is there a difference between a Serial Port stream and a Named Pipe (FIFO)? Especially in regards to Linux?
My understanding is that both:
- Are full duplex
- Can be read/written by process that are unrelated (as opposed to how regular Pipes work)
The only difference I can think of are:
- Serial Ports have file descriptors to actual hardware (that the hardware is reading/writting to) whereas a Named Pipe is just a 'file' created on the kernal to store a data stream then 2 (or more?) processes can connect to and read/write.
- Any other differences if any?
Also if I have one named pipe that I create in one process P1 (and another of my processes P2 connects to it) - can P1 use that one file descriptor to write and read to this named pipe? And P2 can do the same (both read and write). Or do I need to create 2 named pipes if I want P1 to be able to write and read to P2? The practical use is that P1 will write commands to P2 and also read results of those commands from P2 aswell.
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1 Answer
Named Pipe Com Port
Serial ports are for distinct machines to communicate with each other, not for IPC within the same machine. You can configure serial hardware for loopback, but the highest data rates supported by serial port hardware do not come anywhere close to the speed of any modern interconnect -- not USB or eSATA (for other interfaces with 'serial' in their names) nor network interconnects such as ethernet (even wireless). Serial port speed is not even in the same solar system as a FIFO's.
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As far as other characteristics go,
Named Pipe Serial Port
- serial ports will be presented to the system as device files, and FIFOs also will be presented as files
- as such, each can be opened concurrently by multiple unrelated processes, for both reading and writing
- however, you need special privileges to create a serial port special file, plus actual hardware behind it for it to be useful, whereas anyone can make a FIFO
- communication through serial ports is bi-directional; it can be full-duplex, but half-duplex modes are available as well.
- FIFOs are unidirectional, but you can use them in pairs if necessary. In principle, one process could both write to and read from a FIFO, but it would need to be very careful if it wanted to avoid consuming its own messages and to avoid deadlocking.
Bottom line: for bidirectional IPC within one machine, FIFOs are far superior to serial ports. You should also consider a socket interface.
John Bollinger