uio: move docs for this disgraceful failed example to README

Author: cirosantilli

README.adoc

@@ -4858,6 +4858,48 @@ But in part because it is dying, I didn't spend much effort to integrate it into
 
 Maybe some brave soul will send a pull request one day.
 
+=== UIO
+
+UIO is a kernel subsystem that allows to do certain types of driver operations from userland.
+
+This would be awesome to improve debugability and safety of kernel modules.
+
+VFIO looks like a newer and better UIO replacement, but there do not exist any examples of how to use it: https://stackoverflow.com/questions/49309162/interfacing-with-qemu-edu-device-via-userspace-i-o-uio-linux-driver
+
+TODO get something interesting working. I currently don't understand the behaviour very well.
+
+TODO how to ACK interrupts? How to ensure that every interrupt gets handled separately?
+
+TODO how to write to registers. Currently using `/dev/mem` and `lspci`.
+
+This example should handle interrupts from userland and print a message to stdout:
+
+....
+/uio_read.sh
+....
+
+TODO: what is the expected behaviour? I should have documented this when I wrote this stuff, and I'm that lazy right now that I'm in the middle of a refactor :-)
+
+Sources:
+
+* link:kernel_module/user/uio_read.c[]
+* link:rootfs_overlay/uio_read.sh[]
+
+Bibliography:
+
+* https://stackoverflow.com/questions/15286772/userspace-vs-kernel-space-driver
+* https://01.org/linuxgraphics/gfx-docs/drm/driver-api/uio-howto.html
+* https://stackoverflow.com/questions/7986260/linux-interrupt-handling-in-user-space
+* https://yurovsky.github.io/2014/10/10/linux-uio-gpio-interrupt/
+* https://github.com/bmartini/zynq-axis/blob/65a3a448fda1f0ea4977adfba899eb487201853d/dev/axis.c
+* https://yurovsky.github.io/2014/10/10/linux-uio-gpio-interrupt/
+* http://nairobi-embedded.org/uio_example.html that website has QEMU examples for everything as usual. The example has a kernel-side which creates the memory mappings and is used by the user.
+* https://stackoverflow.com/questions/49309162/interfacing-with-qemu-edu-device-via-userspace-i-o-uio-linux-driver
+* userland driver stability questions:
+** https://stackoverflow.com/questions/8030758/getting-kernel-version-from-linux-kernel-module-at-runtime/45430233#45430233
+** https://stackoverflow.com/questions/37098482/how-to-build-a-linux-kernel-module-so-that-it-is-compatible-with-all-kernel-rele/45429681#45429681
+** https://liquidat.wordpress.com/2007/07/21/linux-kernel-2623-to-have-stable-userspace-driver-api/
+
 === Linux kernel interactive stuff
 
 [[fbcon]]

kernel_module/user/uio_read.c

@@ -1,32 +1,4 @@
-/*
-TODO get working. Currently I don't understand the behaviour.
-
-TODO how to ACK interrupts? How to ensure that every interrupt gets handled separately?
-
-TODO write to registers. Currently using /dev/mem and lspci.
-
-Handle interrupts from userland and print a message to stdout.
-
-- Userland driver
-- https://stackoverflow.com/questions/15286772/userspace-vs-kernel-space-driver
-- https://01.org/linuxgraphics/gfx-docs/drm/driver-api/uio-howto.html
-- https://stackoverflow.com/questions/7986260/linux-interrupt-handling-in-user-space
-- https://yurovsky.github.io/2014/10/10/linux-uio-gpio-interrupt/
-- https://github.com/bmartini/zynq-axis/blob/65a3a448fda1f0ea4977adfba899eb487201853d/dev/axis.c
-- https://yurovsky.github.io/2014/10/10/linux-uio-gpio-interrupt/
-- http://nairobi-embedded.org/uio_example.html that website has QEMU examples for everything as usual. The example has a kernel-side which creates the memory mappings and is used by the user.
-- https://stackoverflow.com/questions/49309162/interfacing-with-qemu-edu-device-via-userspace-i-o-uio-linux-driver
-
-Userland driver stability questions:
-
-- https://stackoverflow.com/questions/8030758/getting-kernel-version-from-linux-kernel-module-at-runtime/45430233#45430233
-- https://stackoverflow.com/questions/37098482/how-to-build-a-linux-kernel-module-so-that-it-is-compatible-with-all-kernel-rele/45429681#45429681
-- https://liquidat.wordpress.com/2007/07/21/linux-kernel-2623-to-have-stable-userspace-driver-api/
-
-VFIO looks like the newer UIO replacement, but there are no examples out there anywhere:
-
-- https://stackoverflow.com/questions/49309162/interfacing-with-qemu-edu-device-via-userspace-i-o-uio-linux-driver
-*/
+/* https://github.com/cirosantilli/linux-kernel-module-cheat#uio */
 
 #if 1
 

rootfs_overlay/uio_read.sh

@@ -1,5 +1,6 @@
 #!/bin/sh
-set -ex
+# https://github.com/cirosantilli/linux-kernel-module-cheat#uio
+set -e
 modprobe uio_pci_generic
 # pci_min device
 echo '1234 11e9' > /sys/bus/pci/drivers/uio_pci_generic/new_id
@@ -13,3 +14,4 @@ devmem "0x${base}" w 0x12345678
 devmem "0x$(($base + 4))" w 0x12345678
 devmem "0x${base}" w 0x12345678
 devmem "0x$(($base + 4))" w 0x12345678
+modprobe -r uio_pci_generic