[PATCH 1/5] classes: jobserver: support gnu make fifo jobserver

["Martin Hundebøll" <martin@geanix.com>]

Add a class to implement the gnu make fifo style jobserver. The class
can be activated by symply adding an `INHERIT += "jobserver"` to the
local configuration.

Furthermore, one can configure an external jobserver (i.e. a server
shared between multiple builds), by configured the `JOBSERVER_FIFO`
variable to point at an existing jobserver fifo.

The jobserver class uses the fifo style jobserver, which doesn't require
passing open file descriptors around. It does, however, require
make-4.4, which isn't available in common distro yet. To work around
this, the class make all recipes (except make and its dependencies
itself) depend on `virtual/make-native`.

Signed-off-by: Martin Hundebøll <martin@geanix.com>
---
 meta/classes-global/jobserver.bbclass | 80 +++++++++++++++++++++++++++
 meta/conf/bitbake.conf                |  2 +-
 2 files changed, 81 insertions(+), 1 deletion(-)
 create mode 100644 meta/classes-global/jobserver.bbclass

diff --git a/meta/classes-global/jobserver.bbclass b/meta/classes-global/jobserver.bbclass
new file mode 100644
index 0000000000..c76909fe50
--- /dev/null
+++ b/meta/classes-global/jobserver.bbclass
@@ -0,0 +1,80 @@
+JOBSERVER_FIFO ?= ""
+JOBSERVER_FIFO[doc] = "Path to external jobserver fifo to use instead of creating a per-build server."
+
+addhandler jobserver_setup_fifo
+jobserver_setup_fifo[eventmask] = "bb.event.ConfigParsed"
+
+python jobserver_setup_fifo() {
+    # don't setup a per-build fifo, if an external one is configured
+    if d.getVar("JOBSERVER_FIFO"):
+        return
+
+    # don't use a job-server if no parallelism is configured
+    jobs = oe.utils.parallel_make(d)
+    if jobs in (None, 1):
+        return
+
+    # reduce jobs by one as a token has implicitly been handed to the
+    # process requesting tokens
+    jobs -= 1
+
+    fifo = d.getVar("TMPDIR") + "/jobserver_fifo"
+
+    # and old fifo might be lingering; remove it
+    if os.path.exists(fifo):
+        os.remove(fifo)
+
+    # create a new fifo to use for communicating tokens
+    os.mkfifo(fifo)
+
+    # fill the fifo with the number of tokens to hand out
+    wfd = os.open(fifo, os.O_RDWR)
+    written = os.write(wfd, b"+" * jobs)
+    if written != (jobs):
+        bb.error("Failed to fil make fifo: {} != {}".format(written, jobs))
+
+    # configure the per-build fifo path to use
+    d.setVar("JOBSERVER_FIFO", fifo)
+}
+
+python () {
+    # don't configure the fifo if none is defined
+    fifo = d.getVar("JOBSERVER_FIFO")
+    if not fifo:
+        return
+
+    # avoid making make-native or its dependencies depend on make-native itself
+    if d.getVar("PN") in (
+                "make-native",
+                "libtool-native",
+                "pkgconfig-native",
+                "automake-native",
+                "autoconf-native",
+                "m4-native",
+                "texinfo-dummy-native",
+                "gettext-minimal-native",
+                "quilt-native",
+                "gnu-config-native",
+            ):
+        return
+
+    # don't make unwilling recipes depend on make-native
+    if d.getVar('INHIBIT_DEFAULT_DEPS', False):
+        return
+
+    # make other recipes depend on make-native to make sure it is new enough to
+    # support the --jobserver-auth=fifo:<path> syntax (from make-4.4 and onwards)
+    d.appendVar("DEPENDS", " virtual/make-native")
+
+    # disable the "-j <jobs>" flag, as that overrides the jobserver fifo tokens
+    d.setVar("PARALLEL_MAKE", "")
+    d.setVar("PARALLEL_MAKEINST", "")
+
+    # set and export the jobserver in the environment
+    d.appendVar("MAKEFLAGS", " --jobserver-auth=fifo:" + fifo)
+    d.setVarFlag("MAKEFLAGS", "export", "1")
+
+    # ignore the joberserver argument part of MAKEFLAGS in the hash, as that
+    # shouldn't change the build output
+    d.appendVarFlag("MAKEFLAGS", "vardepvalueexclude", "| --jobserver-auth=fifo:" + fifo)
+}
diff --git a/meta/conf/bitbake.conf b/meta/conf/bitbake.conf
index 6f180d18b0..23a016b31e 100644
--- a/meta/conf/bitbake.conf
+++ b/meta/conf/bitbake.conf
@@ -960,7 +960,7 @@ BB_HASHEXCLUDE_COMMON ?= "TMPDIR FILE PATH PWD BB_TASKHASH BBPATH BBSERVER DL_DI
     BB_WORKERCONTEXT BB_LIMITEDDEPS BB_UNIHASH extend_recipe_sysroot DEPLOY_DIR \
     SSTATE_HASHEQUIV_METHOD SSTATE_HASHEQUIV_REPORT_TASKDATA \
     SSTATE_HASHEQUIV_OWNER CCACHE_TOP_DIR BB_HASHSERVE GIT_CEILING_DIRECTORIES \
-    OMP_NUM_THREADS BB_CURRENTTASK"
+    OMP_NUM_THREADS BB_CURRENTTASK JOBSERVER_FIFO"
 BB_BASEHASH_IGNORE_VARS ?= "${BB_HASHEXCLUDE_COMMON} PSEUDO_IGNORE_PATHS BUILDHISTORY_DIR \
     SSTATE_DIR SOURCE_DATE_EPOCH RUST_BUILD_SYS RUST_HOST_SYS RUST_TARGET_SYS"
 BB_HASHCONFIG_IGNORE_VARS ?= "${BB_HASHEXCLUDE_COMMON} DATE TIME SSH_AGENT_PID \
-- 
2.44.0