kernel modules: add a quick scull port from LDD3

Also:

* fix fops.c on both kernels:
  * 5.9: the out of space error code was 1 not 8
  * 6.6: for whatever reason we can't read the user buffer as before on the
         diagnostic print, it leads to segfault and oops
* create memfile.c which is like fops.c but of unlimited size

rootfs_overlay/lkmc/character_device.sh

@@ -1,7 +1,7 @@
 #!/bin/sh
 set -e
 insmod character_device.ko
-/mknoddev.sh lkmc_character_device
+./mknoddev.sh lkmc_character_device
 [ "$(cat /dev/lkmc_character_device)" = 'abcd' ]
 rm /dev/lkmc_character_device
 rmmod character_device

rootfs_overlay/lkmc/fops.sh

@@ -3,7 +3,9 @@ set -e
 
 # Setup
 f=/sys/kernel/debug/lkmc_fops
-insmod fops.ko
+mod="${1:-fops.ko}"
+shift
+insmod "$mod" "$@"
 
 # read
 [ "$(cat "$f")" = abcd ]
@@ -18,7 +20,7 @@ set +e
 printf 12345 > "$f"
 exit_status="$?"
 set -e
-[ "$exit_status" -eq 8 ]
+[ "$exit_status" -eq 1 ]
 [ "$(cat "$f")" = abcd ]
 
 # seek
@@ -26,5 +28,12 @@ printf 1234 > "$f"
 printf z | dd bs=1 of="$f" seek=2
 [ "$(cat "$f")" = 12z4 ]
 
+# seek past the end
+printf 1234 > "$f"
+printf xy | dd bs=1 of="$f" seek=6
+[ "$(cat "$f")" = 1234 ]
+
 # Teardown
 rmmod fops
+
+echo passed

rootfs_overlay/lkmc/memfile.sh

@@ -0,0 +1,51 @@
+#!/bin/sh
+set -e
+
+# Helpers
+odraw() (
+  od -A n -t x1 -v "$@" | tr -d '\n' | cut -c 2-
+)
+
+# Setup
+f=/sys/kernel/debug/lkmc_memfile
+mod="${1:-memfile.ko}"
+shift
+insmod "$mod" "$@"
+
+# Starts off empty
+[ -z "$(cat "$f")" ]
+
+# write and check it is there
+printf 12 > "$f"
+[ 12 = "$(cat "$f")" ]
+
+# Append and check that it is there
+printf 34 >> "$f"
+[ 1234 = "$(cat "$f")" ]
+
+# Restart
+printf 56 > "$f"
+[ 56 = "$(cat "$f")" ]
+
+# skip
+printf 1234 > "$f"
+[ 23 = "$(dd if="$f" bs=1 count=2 skip=1)" ]
+
+# seek
+printf 1234 > "$f"
+printf xy | dd bs=1 of="$f" seek=1 conv=notrunc
+[ 1xy4 = "$(cat "$f")" ]
+
+# seek past the end
+printf 1234 > "$f"
+printf xy | dd bs=1 of="$f" seek=6 conv=notrunc
+[ '31 32 33 34 00 00 78 79' = "$(odraw "$f")" ]
+
+# Allocate 1 GB for fun.
+dd if=/dev/zero of="$f" bs=1k count=1M
+[ '00 00' = "$(dd if="$f" bs=1 count=2 skip=500M | odraw)" ]
+
+# Teardown
+rmmod memfile
+
+echo passed

rootfs_overlay/lkmc/scull.sh

@@ -0,0 +1,59 @@
+#!/bin/sh
+set -eux
+
+name=scull
+
+mod="${1:-$name.ko}"
+shift
+insmod "$mod" "$@"
+major="$(awk "\$2==\"$name\" {print \$1}" /proc/devices)"
+
+rm -f /dev/${name}[0-3]
+mknod /dev/${name}0 c $major 0
+mknod /dev/${name}1 c $major 1
+mknod /dev/${name}2 c $major 2
+mknod /dev/${name}3 c $major 3
+
+rm -f /dev/${name}pipe[0-3]
+mknod /dev/${name}pipe0 c $major 4
+mknod /dev/${name}pipe1 c $major 5
+mknod /dev/${name}pipe2 c $major 6
+mknod /dev/${name}pipe3 c $major 7
+
+rm -f /dev/${name}single
+mknod /dev/${name}single c $major 8
+
+rm -f /dev/${name}uid
+mknod /dev/${name}uid c $major 9
+
+rm -f /dev/${name}wuid
+mknod /dev/${name}wuid c $major 10
+
+rm -f /dev/${name}priv
+mknod /dev/${name}priv c $major 11
+
+## scull
+
+f="/dev/${name}0"
+[ -z "$(cat "$f")" ]
+
+# Append starts writing from the start of the 4k block, not like the usual semantic.
+printf asdf > "$f"
+printf qw >> "$f"
+[ qwdf = "$(cat "$f")" ]
+
+# Overwrite first clears everything, then writes to start of 4k block.
+printf asdf > /dev/${name}0
+printf qw > /dev/${name}0
+[ qw = "$(cat "$f")" ]
+
+# Read from the middle
+printf asdf > /dev/${name}0
+[ df = "$(dd if="$f" bs=1 count=2 skip=2 status=none)" ]
+
+# Write to the middle
+printf asdf > "$f"
+printf we | dd of="$f" bs=1 seek=1 conv=notrunc status=none
+[ awef = "$(cat "$f")" ]
+
+echo passed

rootfs_overlay/lkmc/seq_file.sh

@@ -1,7 +1,9 @@
 #!/bin/sh
 set -e
 f=/sys/kernel/debug/lkmc_seq_file
-insmod seq_file.ko
+mod="${1:-seq_file.ko}"
+shift
+insmod "$mod" "$@"
 [ "$(cat "$f")" = "$(printf '0\n1\n2\n')" ]
 [ "$(cat "$f")" = "$(printf '0\n1\n2\n')" ]
 [ "$(dd if="$f" bs=1 count=2 skip=0 status=none)" = "$(printf '0\n')" ]

rootfs_overlay/lkmc/seq_file_single_open.sh

@@ -1,7 +1,9 @@
 #!/bin/sh
 set -e
 f=/sys/kernel/debug/lkmc_seq_file_single_open
-insmod seq_file_single_open.ko
+mod="${1:-seq_file_single_open.ko}"
+shift
+insmod "$mod" "$@"
 [ "$(cat "$f")" = "$(printf 'ab\ncd\n')" ]
 [ "$(dd if="$f" bs=1 count=3 skip=1)" = "$(printf "b\nc\n")" ]
 rmmod seq_file_single_open