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-rw-r--r--Makefile17
-rw-r--r--rules.mak36
2 files changed, 46 insertions, 7 deletions
diff --git a/Makefile b/Makefile
index 3b21c0ea48..6ccdb431a7 100644
--- a/Makefile
+++ b/Makefile
@@ -1028,6 +1028,14 @@ build-manual = $(call quiet-command,CONFDIR="$(qemu_confdir)" sphinx-build $(if
manual-deps = $(wildcard $(SRC_PATH)/docs/$1/*.rst) \
$(wildcard $(SRC_PATH)/docs/$1/*.rst.inc) \
$(SRC_PATH)/docs/$1/conf.py $(SRC_PATH)/docs/conf.py
+# Macro to write out the rule and dependencies for building manpages
+# Usage: $(call define-manpage-rule,manualname,manpage1 manpage2...[,extradeps])
+# 'extradeps' is optional, and specifies extra files (eg .hx files) that
+# the manual page depends on.
+define define-manpage-rule
+$(call atomic,$(foreach manpage,$2,$(MANUAL_BUILDDIR)/$1/$(manpage)),$(call manual-deps,$1) $3)
+ $(call build-manual,$1,man)
+endef
$(MANUAL_BUILDDIR)/devel/index.html: $(call manual-deps,devel)
$(call build-manual,devel,html)
@@ -1041,14 +1049,9 @@ $(MANUAL_BUILDDIR)/specs/index.html: $(call manual-deps,specs)
$(MANUAL_BUILDDIR)/system/index.html: $(call manual-deps,system)
$(call build-manual,system,html)
-$(MANUAL_BUILDDIR)/interop/qemu-ga.8: $(call manual-deps,interop)
- $(call build-manual,interop,man)
-
-$(MANUAL_BUILDDIR)/interop/qemu-nbd.8: $(call manual-deps,interop)
- $(call build-manual,interop,man)
+$(call define-manpage-rule,interop,qemu-ga.8 qemu-nbd.8)
-$(MANUAL_BUILDDIR)/system/qemu-block-drivers.7: $(call manual-deps,system)
- $(call build-manual,system,man)
+$(call define-manpage-rule,system,qemu-block-drivers.7)
$(MANUAL_BUILDDIR)/index.html: $(SRC_PATH)/docs/index.html.in qemu-version.h
@mkdir -p "$(MANUAL_BUILDDIR)"
diff --git a/rules.mak b/rules.mak
index c8558876f3..e39b073d46 100644
--- a/rules.mak
+++ b/rules.mak
@@ -399,3 +399,39 @@ GEN_SUBST = $(call quiet-command, \
%.json: %.json.in
$(call GEN_SUBST)
+
+# Support for building multiple output files by atomically executing
+# a single rule which depends on several input files (so the rule
+# will be executed exactly once, not once per output file, and
+# not multiple times in parallel.) For more explanation see:
+# https://www.cmcrossroads.com/article/atomic-rules-gnu-make
+
+# Given a space-separated list of filenames, create the name of
+# a 'sentinel' file to use to indicate that they have been built.
+# We use fixed text on the end to avoid accidentally triggering
+# automatic pattern rules, and . on the start to make the file
+# not show up in ls output.
+sentinel = .$(subst $(SPACE),_,$(subst /,_,$1)).sentinel.
+
+# Define an atomic rule that builds multiple outputs from multiple inputs.
+# To use:
+# $(call atomic,out1 out2 ...,in1 in2 ...)
+# <TAB>rule to do the operation
+#
+# Make 4.3 will have native support for this, and you would be able
+# to instead write:
+# out1 out2 ... &: in1 in2 ...
+# <TAB>rule to do the operation
+#
+# The way this works is that it creates a make rule
+# "out1 out2 ... : sentinel-file ; @:" which says that the sentinel
+# depends on the dependencies, and the rule to do that is "do nothing".
+# Then we have a rule
+# "sentinel-file : in1 in2 ..."
+# whose commands start with "touch sentinel-file" and then continue
+# with the rule text provided by the user of this 'atomic' function.
+# The foreach... is there to delete the sentinel file if any of the
+# output files don't exist, so that we correctly rebuild in that situation.
+atomic = $(eval $1: $(call sentinel,$1) ; @:) \
+ $(call sentinel,$1) : $2 ; @touch $$@ \
+ $(foreach t,$1,$(if $(wildcard $t),,$(shell rm -f $(call sentinel,$1))))