A pair of virtual character devices acting as a loop.
Christophe BLAESS 2019 https://www.blaess.fr/christophe/
This very simple module create a pair of virtual character devices
/dev/charloop0 and /dev/charloop1.
What is written into /dev/charloop0 is readable from
/dev/charloop1 and vice versa.
The devices accept select() system call.
They look quite similar to a fifo (named pipe), but they are seen
as character devices, not as special files and it may be important
in some cases. A second difference: opening a device for writing
does NOT block until a reader opens the other side. There's an internal
buffer which size (default 16 kB) is configurable with the buffer_size
module parameter.
For example I use the devices to have a console access on the virtual serial port of a Qemu session.
I run quemu-system-arm with the parameter -serial /dev/charloop0
and in another terminal I run minicom -D /dev/charloop1.
Another use of this project is during training sessions on kernel
drivers to show the poll() system call implementation.
This software is distributed under the terms of the Gnu GPL v.2 license.
$ ls
charloop.c Makefile README.md
$ make
[...]
$ ls
charloop.c charloop.ko charloop.mod.c charloop.mod.o charloop.o Makefile modules.order Module.symvers README.md
$ sudo insmod charloop.ko
$ echo HELLO > /dev/charloop0
$ cat /dev/charloop1
HELLO
^C
$ echo HELLO > /dev/charloop1
$ cat /dev/charloop0
HELLO
^C
$