Having issues trying to simulate a ttyACM0 device

[joaofl]

I've been trying to use the umockdev (v14.1) lib to mock a ttyACM0 device on an ARM based platform with Yocto. I first included the recipe, compiled, deployed and installed it on the remote host, and so far it seems to work just fine.

The target device is connected to a second device through USB, and a C program interfaces /manages a scanner of RFIDs connected to /dev/ttyACM0.

In order to get the traces a first run:

umockdev-record /dev/ttyACM0 > ttyACM0.umockdev
umockdev-record -s /dev/ttyACM0=ttyACM0.script -i /dev/ttyACM0=ttyACM0.ioctl -- /home/root/scanner-reader

and after recording the main operations I want to reproduce, I try to run it with:

umockdev-run -d ttyACM0.umockdev -s /dev/ttyACM0=ttyACM0.script  -- /home/root/scanner-reader

However, as the scanner-reader progrtam loads, I'm getting errors. Mainly in two parts of the code:

if (ioctl(fd, FIONREAD, &bytesAvailable) < 0) {
        LOG_WARN("ioctl(FIONREAD) for %s failed with errno %d: %s", portName, errno, strerror(errno));

throws the error:
ioctl(FIONREAD) for /dev/ttyACM0 failed with errno 25: Inappropriate ioctl for device

And when I try to read the file descriptor fd with read(fd, buffer, maxLength)

I get the error:
Read error on /dev/ttyACM0 (9): Bad file descriptor

Do you have any Idea why, and or suggestion on how to overcome this?

Thanks in advance!
By the way, congrats for the nice tool!

[martinpitt]

I'm afraid the FIONREAD ioctl isn't implemented in umockdev. This also isn't trivial to add, it would essentially require reimplementing a significant part of the tty layer. ioctl emulation is rather difficult for a program like umockdev, and I only really did it for usbdevfs and evdev (as I needed these for my projects). Contributions appreciated of course 😉

I suppose your recorded ttyACM0.ioctl doesn't actually contain anything, or much of value?

script recording on a TTY (without ioctls) should work though. Does your ttyACM0.script look reasonable? Can you run the umockdev-run scanner-reader call with UMOCKDEV_DEBUG=script and put the output here? Adding an strace in between also can't hurt to see what it's trying to do.

[benzea]

You could look at #125, or, if you are not dealing with a lot of ioctl's also possibly emulating it yourself once there is public API to do so in 0.16, see #132.

[martinpitt]

@joaofl Do the two comments above help? Is this still relevant with current versions?

[joaofl]

Thanks @benzea for the tip, and @martinpitt for checking this out.
Back when I was working with that, I could not emulate the device successful, with umockdev, so I implemented a tool to parse and log the data input, such that I could play it back later on. So honestly speaking, I did not check if @benzea tips could address that problem.

[martinpitt]

Thanks @joaofl . I close this for now, I'm happy to reopen if/when you ever get back to this, just yell here please.