[OE-core] [PATCH V3 04/11] ccache.bbclass: Make it can be shared between different builds

[Robert Yang]

CCACHE_BASEDIR: ccache removes this from file path, so that hashes will be
                the same in different build dirs.

CCACHE_TOP_DIR: Set it to a shared location for different builds.

Signed-off-by: Robert Yang <liezhi.yang at windriver.com>
---
 meta/classes/ccache.bbclass | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/meta/classes/ccache.bbclass b/meta/classes/ccache.bbclass
index 59e1022..f3612c5 100644
--- a/meta/classes/ccache.bbclass
+++ b/meta/classes/ccache.bbclass
@@ -8,8 +8,28 @@
 #   Add the following line to the recipe if it can't be built with ccache:
 #   CCACHE_DISABLE = '1'
 #
+# - Share ccache files between different builds
+#   Set CCACHE_TOP_DIR to a shared dir
+#   CCACHE_TOP_DIR = /path/to/shared_ccache/
+#
+# - TO debug ccahe
+#   export CCACHE_DEBUG = "1"
+#   export CCACHE_LOGFILE = "${CCACHE_DIR}/logfile.log"
+#   And also set PARALLEL_MAKE = "-j 1" to get make the log in order
+#
+
+# Set it to a shared location for different builds, so that cache files can
+# be shared between different builds.
+CCACHE_TOP_DIR ?= "${TMPDIR}/ccache"
+
+# ccahe removes CCACHE_BASEDIR from file path, so that hashes will be the same
+# in different builds.
+export CCACHE_BASEDIR ?= "${TMPDIR}"
+
+# Used for sharing cache files after compiler is rebuilt
+export CCACHE_COMPILERCHECK ?= "%compiler% -dumpspecs"
 
-export CCACHE_DIR ?= "${TMPDIR}/ccache/${MULTIMACH_TARGET_SYS}/${PN}"
+export CCACHE_DIR ?= "${CCACHE_TOP_DIR}/${MULTIMACH_TARGET_SYS}/${PN}"
 
 # We need to stop ccache considering the current directory or the
 # debug-prefix-map target directory to be significant when calculating
-- 
2.7.4