module parameters working except for array

Author: cirosantilli

book.md

@@ -225,3 +225,11 @@ loses text layer
 get number of pages of djvu:
 
     djvm -l speak\ chinese\ 2.djvu | sed -nre '$ s/.+#([0-9]+).+/\1/p'
+
+# pdfcrop
+
+remove empty margins of pdf files
+
+greatly increases filesize (10x)
+
+	pdfcrop a.pdf

image/index.md

@@ -238,6 +238,10 @@ bottom 50 percent:
 
 ### color
 
+- `-colorspace Gray`: convert to grayscale
+
+    convert in.png -colorspace Gray out.png
+
 - `-monochrome`: monochrome image. == -depth 1? but not in practice =)
 
 - `-depth`: number of bits per pixel.

kernel-module/cheat.c

@@ -6,14 +6,14 @@
 override IN_DIR 	?= ./
 override IN_EXTS 	?= .c
 override LOG_PATH 	?= /var/log/syslog
-override OUT_DIR 	:= ./
-#override OUT_DIR 	:= _out/
-override OUT_EXT 	:= .ko
-override OBJ_EXT 	:= .o
-override RUN		?= cheat
-
-INS			:= $(filter-out %.mod.c, $(foreach IN_EXT, $(IN_EXTS), $(wildcard $(IN_DIR)*$(IN_EXT))))
-INS			:= $(foreach IN_EXT, $(IN_EXTS), $(wildcard $(IN_DIR)*$(IN_EXT)))
+override OUT_DIR 	?= ./
+#override OUT_DIR 	?= _out/
+override OUT_EXT 	?= .ko
+override OBJ_EXT 	?= .o
+override RUN		?= main
+
+INS		:= $(filter-out %.mod.c, $(foreach IN_EXT, $(IN_EXTS), $(wildcard $(IN_DIR)*$(IN_EXT))))
+INS		:= $(foreach IN_EXT, $(IN_EXTS), $(wildcard $(IN_DIR)*$(IN_EXT)))
 INS_NODIR 	:= $(notdir $(INS))
 OBJS_NODIR	:= $(addsuffix $(OBJ_EXT), $(basename $(INS_NODIR)))
 OBJS		:= $(addprefix $(OUT_DIR), $(OBJS_NODIR))
@@ -23,7 +23,7 @@ RUN_EXT		:= $(RUN)$(OUT_EXT)
 
 #TODO why this does not work but the next line does? there is no `:` version of `+=`: it depends on how it is first defined. If if is first defined with `:`: then `+=` is `:`
 #obj-m 	+= $(OBJS)
-obj-m += hello_world.o cheat.o
+obj-m += hello_world.o main.o
 
 .PHONY: all clean ins rm run
 
@@ -49,7 +49,8 @@ clean:
 	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
 
 ins: all
-	sudo insmod $(RUN_EXT)
+	sudo insmod $(RUN_EXT) param_i=1 param_s="bbb"
+	#sudo insmod $(RUN_EXT) param_i=1 param_s="bbb" param_is="1,1,1"
 
 # view system log file for printk messages
 log:

kernel-module/.gitignore renamed to kernel/.gitignore

@@ -44,7 +44,7 @@ interpreter, the X server, etc. The extra user space services are specified by t
 of the linux kernel.
 
 You cannot use user space libs such as libc to program the kernel,
-since the kernel itself itself if need to be working for user space to work. TODO confirm
+since the kernel itself itself if need to be working for user space to work.
 
 # user programs
 
@@ -60,6 +60,15 @@ probably via the `write` system call.
 
 Another simple example is file io.
 
+## floating point
+
+you cannto use floating point operations on kernel code because that would incur too much overhead
+of saving floating point registers on some architectures, so don't do it.
+
+## memory
+
+memory is much more restrictive than in user applictions, so be extra cautious to use little memory
+
 # rings
 
 x86 implemented concept
@@ -75,11 +84,68 @@ linux uses 2:
 
 this is used to separate who can do what
 
-# install a new kernel
+# test a new kernel
+
+## compile and install
+
+this is a very slow test mechanism since you need to reboot everytime.
+
+<www.cyberciti.biz/tips/compiling-linux-kernel-26.html>
+
+get the source:
+
+	git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
+
+clean everything:
+
+	make mrproper
+
+generate the `.config` file:
+
+	make menuconfig
+
+this opens up a ncurses interface which allows you to choose amongst tons of options
+which determine which features your kernel will include or not.
+
+then go on to `save` to save to the `.config` file and then exit
+
+build:
+
+	make -j5
+
+`-j` tells make to spawn several process, which is useful if you have a multicore processor.
+it is recommend to use
+
+	n = number of processors + 1
+
+this may take more than one hour.
+
+install:
+
+	sudo make modules_install -j5
+	sudo make install -j5
+
+this will place:
+
+- the compiled kernel under `/boot/vmlinuz-<version>`
+- config file `.config` as `/boot/config-<version>`
+- `System.map` under `/boot/System.map-<version>`.
+
+	This contains symbolic debug information.
+
+- `/lib/modules/<version>/` for the modules
+
+configure grub: TODO
+
+## kernel module
+
+can be inserted and removed while the kernel runs.
 
-TODO
+However, if you make an error at startup (dereference null pointer for example),
+the kernel module may become impossible to reinsert without a reboot.
+<http://unix.stackexchange.com/questions/78858/cannot-remove-or-reinsert-kernel-module-after-error-while-inserting-it-without-r/>
 
-also considering installing a module instead of hacking the kernel if a module would do
+## kernel virtual machine
 
 # get kernel version