On Tue, Feb 18, 2020 at 12:56 PM Marty Leisner <linux@xxxxxxxxxxxxxxxx> wrote: > > I've read tutorials and seen example programs on how to get page information into userspace > (eventually, I'll want to dma from a UIO driver) Instead of using a UIO driver you may want to consider a VFIO driver as you may not be able to access memory directly from the device with a UIO driver if an IOMMU is present in the system. UIO is normally only used for small embedded controllers where you just need MMIO access. > For POC, I have a simple driver with an mmap rule, which does kmalloc on a new buffer. > > The driver can read/write the memory, and the user space program can read/write the memory (and both > sides agree on the data read/written). > > It appears in /proc/self/maps, and when I try to look it up in /proc/self/pagemap, it says its > neither swapped nor present. > > This seems like a clever way -- if it works (the alternative is sloppy ioctl's or other custom > methods) I suggest you just take a look at VFIO. You can find some user documentation here: https://www.kernel.org/doc/html/latest/driver-api/vfio.html There are multiple userspace drivers out there that make use of UIO or VFIO functionality. If you are in need of examples just go take a look at the DPDK project (http://git.dpdk.org/dpdk/) as they have all of their NIC drivers implemented in userspace and are using either a igb_uio driver or vfio driver to connect to them.
