sync

Author: cirosantilli

README.md

@@ -26,6 +26,7 @@ Includes Linux concepts and utilities that work on Linux, not necessarily in the
         1. [Android](android.md)
     1.  [Distros](distros.md)
         1. [Minimal distros](minimal-distros.md)
+        1. [Buildroot](buildroot.md)
     1.  [Linux runs on](linux-runs-on.md)
     1.  [Runs Linux](runs-linux.md)
 1.  [Kernel](kernel/)

alternatives.md

@@ -18,6 +18,8 @@ Strict real time:
 - <https://en.wikipedia.org/wiki/FreeRTOS>
 - <https://en.wikipedia.org/wiki/Micro-Controller_Operating_Systems> proprietary with source available
 
+<https://en.wikipedia.org/wiki/Xenomai> provides real time capabilities on Linux userland.
+
 Dedicated OSes / firmware:
 
 - <https://en.wikipedia.org/wiki/Rockbox> , music players

buildroot.md

@@ -0,0 +1,129 @@
+# Buildroot
+
+Run two commands, get a Linux distro built from source.
+
+1.  Examples
+    1. [Add a new package in tree](https://github.com/cirosantilli/buildroot/tree/in-tree-package-2016.05)
+    1. [Package with a Kernel module in tree](https://github.com/cirosantilli/buildroot/tree/kernel-module-2016.05)
+    1. [Out of tree package](https://github.com/cirosantilli/buildroot/tree/out-of-tree-2016.05)
+
+## Introduction
+
+Takes care of:
+
+- cross compilation. In other words, compiles GCC for you. Several archs supported.
+- bootloading. Several bootloaders supported.
+- root filesystem generation.
+- tons of packages, e.g. X.org. Packages have a dependency system, but no versioning.
+
+Lots of software supported.
+
+## QEMU example
+
+Tested on Ubuntu 16.04.
+
+    git clone git://git.buildroot.net/buildroot
+    cd buildroot
+    git checkout 2016.05
+    make qemu_x86_64_defconfig
+    # Can't use -jN, use `BR2_JLEVEL=2` instead.
+    make BR2_JLEVEL=2
+    # Wait.
+    # cat board/qemu/x86_64/readme.txt
+    qemu-system-x86_64 -M pc -kernel output/images/bzImage -drive file=output/images/rootfs.ext2,if=virtio,format=raw -append root=/dev/vda -net nic,model=virtio -net user
+
+## ARM
+
+The obvious x86 analog just works, beauty.
+
+The only thing is that you have to move the x86 output away if you have one:
+
+    mv output output.x86~
+    make qemu_arm_versatile_defconfig
+    make
+    qemu-system-arm -M versatilepb -kernel output/images/zImage -dtb output/images/versatile-pb.dtb -drive file=output/images/rootfs.ext2,if=scsi,format=raw -append "root=/dev/sda console=ttyAMA0,115200" -serial stdio -net nic,model=rtl8139 -net user
+
+Then in QEMU:
+
+    cat /proc/cpuinfo
+
+## Don't ask for password at login
+
+<http://unix.stackexchange.com/questions/299408/how-to-login-automatically-without-typing-root-in-buildroot-x86-64-qemu>
+
+## config
+
+All options are stored in `.config` before build. The `.config` file fully specifies the entire system.
+
+Make and environment variables *don't* in general override options:
+
+    # Does not work.
+    #make defconfig BR2_SOME_OPT=y
+
+Whenever you do `make`, `make oldconfig` gets run. `make oldconfig` removes any new options you've added to the file, unless they are specified under `package/Config.in`.
+
+Some configs are not put on the `.config`, while others are commented out. TODO: commented out means dependencies and have been met, removed not?
+
+### Important configurations
+
+    LINUX_KERNEL_VERSION="4.5.3"
+    BR2_GCC_VERSION_4_9_X=y
+
+## Add a file to the distro
+
+    mkdir a
+    mkdir a/b
+    date >a/b/c
+    make BR2_ROOTFS_OVERLAY='a'
+
+Outcome: the root of the generated filesystem now contains `/b/c`.
+
+## Permanent storage filesystem
+
+TODO
+
+## Remove package
+
+Currently impossible.
+
+For simple cases, just remove the files from:
+
+    rm output/target/usr/bin/hello
+
+## random: nonblocking pool is initialized
+
+TODO how to stop printing that
+
+## Projects that use Buildroot:
+
+- <https://en.wikipedia.org/wiki/OpenWrt>
+
+## Games
+
+Placed under `/usr/bin` and `/usr/games`.
+
+Grouped under `packages/Config.in`:
+
+    menu "Games"
+
+Many / all are SDL based. It seems that SDL has an `fbdev` mode that dispenses X11.
+
+### ltris
+
+### lbreakout2
+
+Fails with:
+
+    set_video_mode: cannot allocate screen: Couldn't set console screen info
+
+### opentyrian
+
+Hangs.
+
+### sl
+
+Classic steam locomotive `sl` typo corrector. Text only.
+
+## X11
+
+http://unix.stackexchange.com/questions/70931/install-x11-on-my-own-linux-system

ffmpeg.md

@@ -8,6 +8,18 @@ List codecs: <http://stackoverflow.com/questions/3377300/what-are-all-codecs-sup
 
     ffmpeg -codecs
 
+## stdin and stdout operations
+
+ffmpeg can detect file types from both file names and contents. But if you want to be explicit, remember the `man ffmpeg` signature:
+
+    ffmpeg [global_options] {[input_file_options] -i input_file} ... {[output_file_options] output_file} ...
+
+So the `-f` before `-i` is for the input format, and the `-f` after `-i` is the output.
+
+Example: stream your desktop and play it:
+
+    ffmpeg -video_size 640x480 -framerate 25 -f x11grab -i :0.0+100,200 -f h264 - | ffplay -f h264 -
+
 ## Extract raw streams
 
 ### VP9

kernel/Makefile

@@ -4,7 +4,8 @@
     1. [main.c](main.c)
     1. [hello_world](hello_world.c)
 1.  [Introduction](introduction.md)
-1.  [Makefile](makefile.md)
+1.  [Build](build.md)
+1.  [Use built kernel](use-built-kernel.md)
 1.  [Source tree](source-tree.md)
 1.  [Testing](testing.md)
 1.  [Module](module.md)

kernel/README.md

@@ -1,4 +1,4 @@
-# Makefile
+# Build
 
 How to compile and install the kernel.
 
@@ -254,33 +254,6 @@ Can be configured with:
 
 Make sure to point to the `../build` so that `.config` is seen
 
-### isoimage
-
-### ISO build
-
-For x86 (why only x86), you can generate a bootable ISO with:
-
-    make isoimage FDINITRD=rootfs.cpio.gz
-
-where `FINITRD` points to a previously constructed `initrd` that will be used to initialize the system.
-
-This method is used by [Minimal Linux Live](https://github.com/ivandavidov/minimal), which producesa nice little `rootfs.cpio.gz`.
-
-The output file generated is:
-
-    build/arch/x86/boot/image.iso
-
-You can then feed the generated ISO directly to QEMU with either:
-
-    qemu-system-x86_64 -cdrom image.iso
-    qemu-system-x86_64 -hda image.iso
-
-or burn it to either an USB or CD with:
-
-    sudo dd if=image.iso of=/dev/sdX
-
-Internally in 4.2, it is coded at `arch/x86/boot/Makefile`, and `syslinux`, `mkisofs` to make a ISO, and then `isohybrid` to make it bootable either from ISO or USB.
-
 ### Headers install
 
 ### headers_install