sketch uio

kernel_config_fragment

@@ -135,3 +135,30 @@ CONFIG_PCI=y
 
 # Like CONFIG_X86_PTDUMP for ARM.
 CONFIG_ARM64_PTDUMP=y
+
+## UIO
+
+# Userspace drivers.
+#
+# Superseded by the more featureful VFIO.
+#
+# Documentation/DocBook/uio-howto.tmpl
+#
+# UIO interface in a nutshell:
+#
+# - blocking read / poll: waits until interrupts
+# - write: call irqcontrol callback. Default: 0 or 1 to enable / disable interrupts.
+# - mmap: access device memory
+
+# All other UIO depend on this module.
+CONFIG_UIO=m
+
+# Generic platform devices.
+# https://yurovsky.github.io/2014/10/10/linux-uio-gpio-interrupt/
+CONFIG_UIO_DMEM_GENIRQ=m
+CONFIG_UIO_PDRV_GENIRQ=m
+
+# https://github.com/rumpkernel/wiki/wiki/Howto:-Accessing-PCI-devices-from-userspace
+# /sys/class/uio/
+# /sys/class/uio/uio0
+CONFIG_UIO_PCI_GENERIC=m

kernel_module/pci.c

@@ -50,6 +50,12 @@ Often abbreviated to BDF.
 - device: maps to one slot
 - function: https://stackoverflow.com/questions/19223394/what-is-the-function-number-in-pci/44735372#44735372
 
+Sometimes a fourth number is also added, e.g.:
+
+    0000:00:04.0
+
+TODO is that the domain?
+
 Class: pure magic: https://www-s.acm.illinois.edu/sigops/2007/roll_your_own/7.c.1.html
 TODO: does it have any side effects? Set in the edu device at:
 
@@ -279,6 +285,7 @@ static int pci_probe(struct pci_dev *dev, const struct pci_device_id *id)
 		 * - https://stackoverflow.com/questions/17913679/how-to-instantiate-and-use-a-dma-driver-linux-module
 		 * - https://stackoverflow.com/questions/5539375/linux-kernel-device-driver-to-dma-from-a-device-into-user-space-memory
 		 * - RPI userland /dev/mem https://github.com/Wallacoloo/Raspberry-Pi-DMA-Example
+		 * - https://stackoverflow.com/questions/34188369/easiest-way-to-use-dma-in-linux
 		 */
 		{
 			dma_addr_t dma_handle_from, dma_handle_to;

kernel_module/user/pagemap_dump.c

@@ -5,6 +5,7 @@ Adapted from: https://github.com/dwks/pagemap/blob/8a25747bc79d6080c8b94eac80807
 
 - https://stackoverflow.com/questions/17021214/how-to-decode-proc-pid-pagemap-entries-in-linux/45126141#45126141
 - https://stackoverflow.com/questions/5748492/is-there-any-api-for-determining-the-physical-address-from-virtual-address-in-li
+- https://stackoverflow.com/questions/6284810/proc-pid-pagemaps-and-proc-pid-maps-linux/45500208#45500208
 
 Dump the page map of a given process PID.
 

kernel_module/user/uio_read.c

@@ -0,0 +1,46 @@
+/*
+Adapted from: https://yurovsky.github.io/2014/10/10/linux-uio-gpio-interrupt/
+
+    modprobe uio_pdrv_genirq
+
+TODO get working.
+
+Handle interrupts from userland and print a message to stdout.
+*/
+
+#define _XOPEN_SOURCE 700
+#include <fcntl.h> /* open */
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h> /* write */
+
+int main(int argc, char **argv)
+{
+
+    char *dev;
+    if (argc < 2) {
+    }
+    int fd = open("/dev/uio", O_RDWR);
+    if (fd < 0) {
+        perror("open");
+        exit(EXIT_FAILURE);
+    }
+    while (1) {
+        uint32_t info = 1;
+        size_t nb = write(fd, &info, sizeof(info));
+        if (nb < sizeof(info)) {
+            perror("write");
+            close(fd);
+            exit(EXIT_FAILURE);
+        }
+        nb = read(fd, &info, sizeof(info));
+        if (nb == sizeof(info)) {
+            printf("Interrupt #%u\n", info);
+        }
+    }
+    close(fd);
+    exit(EXIT_SUCCESS);
+}

rootfs_overlay/character_device.sh

@@ -1,6 +1,6 @@
 #!/bin/sh
 insmod /character_device.ko
-/mknoddev.sh character_device
+/mknoddev.sh lkmc_character_device
 cat /dev/lkmc_character_device
 # => abcd
 rm /dev/lkmc_character_device

rootfs_overlay/mknoddev.sh

@@ -1,4 +1,4 @@
 #!/bin/sh
-dev="lkmc_$1"
+dev="$1"
 major="$(grep "$dev" /proc/devices | cut -d ' ' -f 1)"
 mknod "/dev/$dev" c "$major" 0

rootfs_overlay/pci.sh

@@ -11,7 +11,7 @@ cat /proc/interrupts
 
 # Setup.
 insmod /pci.ko
-/mknoddev.sh pci
+/mknoddev.sh lkmc_pci
 
 # Shows that this module owns the PCI device.
 lspci -k