Linux user space PCI driver

Question

I'm trying to write a PCI device driver that runs in user space. Not my idea, what the client wants. Target is an embedded Linux board that will never have more than a single user. I'm an experienced C programmer and know Linux, just not familiar with Linux driver development.

Is this really a device driver or just a library? Do I need to use the typical calls pci_register_driver, etc. or can I just access the device using fopen, and using mmap and ioperm to get to it?

Interrupts will be done using the MSI model. Also need to handle DMA transfers. The device will be streaming lots of data to the user.

There's not much info out there on this subject, LDD3 only devotes a couple of pages to it, and there's nothing else that I could find here on SO.

Thanks in advance!

Answer 1

If there is no driver handling the PCI card it would be possible to access it using ioperm (or iopl - depending on the address) if only port accesses are required.

Using DMA and interrupts is definitely impossible without a kernel-mode driver.

By googleing I found some text about something like a "generic kernel-mode driver" that allows writing user-mode drivers (including DMA and interrupts).

You should ask your customer which kind of kernel-mode drivers for accessing PCI cards is installed on the Linux board.

Answer 2

There is now a proper way to do high performance userspace PCI drivers, called vfio. There is not much documentation, but see the kernel docs http://lxr.free-electrons.com/source/Documentation/vfio.txt and the header file /usr/include/linux.vfio.h. It is available since Linux 3.6.