從Hello World來理解bitbake的處理過程:
1.安裝Bitbake並設定PATH
使用git下載 bitbake並安裝
$git clone git://git.openembedded.org/bitbake
設定PATH
$export PATH=/home/<your directory>/bitbake/bin:$PATH
2. 新建一個工作目錄，並試著run bitbake
$mkdir ~/hello
$cd hello
$bitbake
會出現下面的錯誤訊息
The BBPATH variable is not set and bitbake did not
find a conf/bblayers.conf file in the expected location.
Maybe you accidentally invoked bitbake from the wrong directory?
DEBUG: Removed the following variables from the environment:
GNOME_DESKTOP_SESSION_ID, XDG_CURRENT_DESKTOP,
GNOME_KEYRING_CONTROL, DISPLAY, SSH_AGENT_PID, LANG, no_proxy,
XDG_SESSION_PATH, XAUTHORITY, SESSION_MANAGER, SHLVL,
MANDATORY_PATH, COMPIZ_CONFIG_PROFILE, WINDOWID, EDITOR,
GPG_AGENT_INFO, SSH_AUTH_SOCK, GDMSESSION, GNOME_KEYRING_PID,
XDG_SEAT_PATH, XDG_CONFIG_DIRS, LESSOPEN, DBUS_SESSION_BUS_ADDRESS,
_, XDG_SESSION_COOKIE, DESKTOP_SESSION, LESSCLOSE, DEFAULTS_PATH,
UBUNTU_MENUPROXY, OLDPWD, XDG_DATA_DIRS, COLORTERM, LS_COLORS
當我們啟動 bitbake時，它會試著去找medtata files。而BBPATH就是指示那些檔案放那的變數。
如果沒有設定它，bitbake不知去那找.conf和.bb。
2.設定BBPATH，run bitbake
$BBPATH="/home/<your directory>/hello"
$export BBPATH
$bitbake
ERROR: Traceback (most recent call last):
File "/home/scott-lenovo/bitbake/lib/bb/cookerdata.py", line 163, in wrapped
return func(fn, *args)
File "/home/scott-lenovo/bitbake/lib/bb/cookerdata.py", line 173, in parse_config_file
return bb.parse.handle(fn, data, include)
File "/home/scott-lenovo/bitbake/lib/bb/parse/__init__.py", line 99, in handle
return h['handle'](fn, data, include)
File "/home/scott-lenovo/bitbake/lib/bb/parse/parse_py/ConfHandler.py", line 120, in handle
abs_fn = resolve_file(fn, data)
File "/home/scott-lenovo/bitbake/lib/bb/parse/__init__.py", line 117, in resolve_file
raise IOError("file %s not found in %s" % (fn, bbpath))
IOError: file conf/bitbake.conf not found in /home/scott-lenovo/hello
ERROR: Unable to parse conf/bitbake.conf: file conf/bitbake.conf not found in /home/scott-lenovo/hello
找不到conf/bitbake.conf，而這個檔案應該建在hello底下。
3.建立conf/bitbake.conf，run bitbake
先在hello底下建立conf資料夾
$ mkdir conf
再在conf下建立bitbake.conf，並輸入底下內容
TMPDIR = "${TOPDIR}/tmp"
CACHE = "${TMPDIR}/cache"
STAMP = "${TMPDIR}/stamps"
T = "${TMPDIR}/work"
B = "${TMPDIR}"
TOPDIR => build directory，也就是hello資料夾
TMPDIR => 建立在build資料夾下
CACHE => 建立在TMPDIR(tmp)資料夾下，儲存Meatadata的cache，讓Bitbake不用每次重新parse
STAMP => 用來建立recipe stamp files
T => 用來放暫存檔的地方，大多是task logs and scriptsS。
B => Bitbake建置recipes時，執行functions的地方
執行Bitbake
$bitbake
ERROR: Traceback (most recent call last):
File "/home/scott-lenovo/bitbake/lib/bb/cookerdata.py", line 163, in wrapped
return func(fn, *args)
File "/home/scott-lenovo/bitbake/lib/bb/cookerdata.py", line 177, in _inherit
bb.parse.BBHandler.inherit(bbclass, "configuration INHERITs", 0, data)
File "/home/scott-lenovo/bitbake/lib/bb/parse/parse_py/BBHandler.py", line 92, in inherit
include(fn, file, lineno, d, "inherit")
File "/home/scott-lenovo/bitbake/lib/bb/parse/parse_py/ConfHandler.py", line 100, in include
raise ParseError("Could not %(error_out)s file %(fn)s" % vars(), oldfn, lineno)
ParseError: ParseError in configuration INHERITs: Could not inherit file classes/base.bbclass
ERROR: Unable to parse base: ParseError in configuration INHERITs: Could not inherit file classes/base.bbclass
這次是找不到classes/base.bbclass。classes是用來放基本的classes，它類似物件導向語言裡的classes。
base.bbclass是用來給每個recipe繼承的。
4.建立classes/base.bbclass，run bitbake
建立classes資料夾
$ cd $HOME/hello
$ mkdir classes
在base.bbclass輸入
addtask build
執行bitbake
$ bitbake
Nothing to do. Use 'bitbake world' to build everything, or run 'bitbake --help' for usage information.
5. 新建一個mylayer和printhello.bb，run bitbake printhello.bb
$ cd $HOME
$ mkdir mylayer
$ cd mylayer
$ mkdir conf
在conf資料夾下新增一個layer.conf並輸入下面內容:
BBPATH .= ":${LAYERDIR}"
BBFILES += "${LAYERDIR}/*.bb"
BBFILE_COLLECTIONS += "mylayer"
BBFILE_PATTERN_mylayer := "^${LAYERDIR}/"
在mylayer資料夾下新增一個printhello.bb並輸入下面內容:
DESCRIPTION = "Prints Hello World"
PN = 'printhello'
PV = '1'
python do_build() {
bb.plain("********************");
bb.plain("* *");
bb.plain("* Hello, World! *");
bb.plain("* *");
bb.plain("********************");
}
執行 bitbake printhello
$ cd $HOME/hello
$ bitbake printhello
ERROR: no recipe files to build, check your BBPATH and BBFILES?
Summary: There was 1 ERROR message shown, returning a non-zero exit code.
因為bitbake不知printhello.bb在那裡。
6.新增bblayers.conf，執行bitbake printhello
在hello/conf底下，新增bblayers.conf告訴bitbake printhello.bb的位置
BBLAYERS ?= " \
/home/<you>/mylayer \
執行 bitbake printhello
$ bitbake printhello
Parsing recipes: 100% |##################################################################################|
Time: 00:00:00
Parsing of 1 .bb files complete (0 cached, 1 parsed). 1 targets, 0 skipped, 0 masked, 0 errors.
NOTE: Resolving any missing task queue dependencies
NOTE: Preparing runqueue
NOTE: Executing RunQueue Tasks
********************
* *
* Hello, World! *
* *
********************
NOTE: Tasks Summary: Attempted 1 tasks of which 0 didn't need to be rerun and all succeeded.
