python 如何使用 /dev/ptmx 创建虚拟串口？
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how to use /dev/ptmx for create a virtual serial port?
提问by linjunhalida
I have a program, using pyserial, and I want to test it without using a real serial port device.
我有一个程序，使用 pyserial，我想在不使用真正的串行端口设备的情况下对其进行测试。
In windows, I use com0com, and in linux, I know there is a method to create virtual serial port pair without using additional program.
在windows中，我使用com0com，在linux中，我知道有一种方法可以在不使用额外程序的情况下创建虚拟串口对。
so I look up the manual, and found pts, /dev/ptmx, but I don't know how to create a pair by following the manual, can anyone give me a example?
所以我查了手册，找到了pts，/dev/ptmx，但我不知道如何按照手册创建一对，谁能给我举个例子？
I tried(in python):
我试过（在python中）：
f = open("/dev/ptmx", "r")
and it works, /dev/pts/4 is created.
它有效，/dev/pts/4 被创建。
and I tried:
我试过：
f = open("/dev/4", "w")
and the result is:
结果是：
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
IOError: [Errno 5] Input/output error: '/dev/pts/4'
edit: I found a solution(workround), using socat.
编辑：我找到了一个解决方案（解决方法），使用 socat。
socat PTY,link=COM8 PTY,link=COM9
then COM8 COM9 are created as virtual serial port pair.
然后将 COM8 COM9 创建为虚拟串行端口对。
采纳答案by Alex Martelli
Per the docs, you need ptsnameto get the name of the slave-side of the pseudo-terminal, and also, quoting the docs,
根据docs，您需要ptsname来获取伪终端从属端的名称，并且还需要引用文档，
Before opening the pseudo-terminal slave, you must pass the master's file descriptor to grantpt(3) and unlockpt(3).
在打开伪终端slave之前，必须将master的文件描述符传递给grantpt(3)和unlockpt(3)。
You should be able to use ctypesto call all of the needed functions.
您应该能够使用ctypes来调用所有需要的函数。
回答by Aquiles
I was trying to make an application that made use of virtual serial ports in order to communicate with some remote devices using TCP/Serial conversion... and I came across to a problem similar to yours. My solution worked out as follows:
我试图制作一个使用虚拟串行端口的应用程序，以便使用 TCP/串行转换与某些远程设备进行通信……但我遇到了与您类似的问题。我的解决方案如下：
import os, pty, serial
master, slave = pty.openpty()
s_name = os.ttyname(slave)
ser = serial.Serial(s_name)
# To Write to the device
ser.write('Your text')
# To read from the device
os.read(master,1000)
Although the name of the port of the master is the same if you check (/dev/ptmx) the fd is different if you create another master, slave pair, so reading from the master gets you the message issued to his assigned slave. I hope this helps you or anyone else that comes across a problem similar to this one.
尽管如果您检查 (/dev/ptmx) 时主端口的名称是相同的，但如果您创建另一个主从对，则 fd 是不同的，因此从主读取可以将消息发送给他指定的从。我希望这可以帮助您或遇到与此问题类似的问题的任何其他人。
回答by t0mm13b
I don't know python but I can point you in the right direction: look hereat a C code sample. Here's the manpage for the /dev/ptmx. Make sure the permissions and owner is correct!. Here is the poster on the linuxquestions forumon how to use it from C.
我不知道 python，但我可以为你指出正确的方向：看看这里的 C 代码示例。这是/dev/ptmx的手册页。确保权限和所有者正确！。这是 linuxquestions论坛上关于如何从 C 使用它的海报。
回答by Thomas Wouters
You should consider using the ptymodule instead, which should take care of this for you. (it opens /dev/ptmx or calls openptyor opens another appropriate device, depending on the platform.)
您应该考虑改用该pty模块，它应该会为您解决这个问题。（它打开 /dev/ptmx 或调用openpty或打开另一个适当的设备，具体取决于平台。）
回答by badp
You could build a dummy object that implements the same interface as the pySerialclasses you use, but do something completely different and easily replicable like reading from and writing to files/terminal/etc.
您可以构建一个虚拟对象，该对象实现与pySerial您使用的类相同的接口，但做一些完全不同且易于复制的事情，例如读取和写入文件/终端等。
For example:
例如：
class DummySerial():
#you should consider subclassing this
def __init__(self, *args, **kwargs):
self.fIn = open("input.raw", 'r')
self.fOut = open("output.raw", 'w')
pass
def read(self, bytes = 1):
return self.fIn.read(bytes)
def write(self, data):
self.fOut.write(data)
def close(self):
self.fIn.close()
self.fOut.close()
#implement more methods here
If it quacks like a duck and it ducks like a duck...
如果它像鸭子一样嘎嘎叫，它像鸭子一样鸭叫......
