Indeed, the project has gone through a few iterations already (It was first a monolithic kernel module that required a secondary module to call into the API and whatnot). I've went towards a more userspace-friendly usage mainly so that you can iterate your changes much, much faster. Creating the synthetic PCI device is as easy as opening the userspace shim you program, it'll then appear on your bus. When you want to test new changes, you close the shim normally (Effectively removing it from the bus) and you can do this process as many times as needed.
Hi, thanks. That's almost it. The remaining problem is just how to tie it together (where do I put the handle_mmio_read pointer or which event should it be handled in?)
PCIEM_EVENT_MMIO_READ is defined but not used anywhere in the codebase
Hi! Sorry, this is an issue on my side; I forgot to update the documentation's example with the latest changes.
You basically have the kernel eventfd notify you about any access triggered (Based on your configuration), so from userspace, you have the eventfd and then you mmap the shared lock-less ring buffer that actually contains the events PCIem notifies (So you don't end up busy polling).
You basically mmap a struct pciem_shared_ring where you'll have your usual head/tail pointers.
From then on, on your main, you'd have a select() or a poll() for the eventfd; when PCIem notifies the userspace you'd check head != tail (Which means there are events to process) and you can basically do:
The documentation still refers to PCIEM_EVENT_MMIO_READ but it's never referenced in the code on the main branch
I'll admit that I asked for a simple compilable example illustrating something simple like the read events because it looks like it's just reading from the shared memory, and maybe generating an event for any read or write access with the PCIEM_EVENT_MMIO_WRITE event type
PCIEM_EVENT_MMIO_READ is kept for reference on the while (head != tail) loop just to remind the user that there can be more than 1 event registered in terms of access type.
Let's say that you register your watchpoint in READ mode (I still have to change the IOCTL for that as currently is hardcoded for writes: attr.bp_type = HW_BREAKPOINT_W), then you'd be consuming PCIEM_EVENT_MMIO_READ events instead of PCIEM_EVENT_MMIO_WRITE.
The fact that the PCIEM_EVENT_MMIO_READ define is there is to help me remind me to incorporate that missing logic.
