contrib: main.mak: Guard downloads with flock.

This is to prevent resource contention on shared file systems such as
NFS.

* contrib/src/main.mak (download) <wget>: Guard with flock.
<curl>: Likewise.
<fetch> Likewise, and properly quote shell arguments.
(download_git): Likewise.

Change-Id: I8e2139d780a34ad054cfa8e188c6cbaf94df0609

contrib/src/main.mak

@@ -250,14 +250,12 @@ SVN ?= $(error subversion client (svn) not found!)
 ifeq ($(DISABLE_CONTRIB_DOWNLOADS),TRUE)
 download = $(error Trying to download $(1) but DISABLE_CONTRIB_DOWNLOADS is TRUE, aborting.)
 else ifeq ($(shell wget --version >/dev/null 2>&1 || echo FAIL),)
-download = wget $(if ${BATCH_MODE},-nv) -t 4 --waitretry 10 -O "$@" "$(1)"
+download = flock "$@.lock" wget $(if ${BATCH_MODE},-nv) -t 4 --waitretry 10 -O "$@" "$(1)"
 else ifeq ($(shell curl --version >/dev/null 2>&1 || echo FAIL),)
-download = curl $(if ${BATCH_MODE},-sS) -f -L --retry-delay 10 --retry 4 -- "$(1)" > "$@"
+download = flock "$@.lock" curl $(if ${BATCH_MODE},-sS) -f -L --retry-delay 10 --retry 4 -- "$(1)" > "$@"
 else ifeq ($(which fetch >/dev/null 2>&1 || echo FAIL),)
-download = rm -f $@.tmp && \
-	fetch -p -o $@.tmp "$(1)" && \
-	touch $@.tmp && \
-	mv $@.tmp $@
+download = flock "$@.lock" sh -c \
+  'rm -f "$@.tmp" && fetch -p -o "$@.tmp" "$(1)" && touch "$@.tmp" && mv "$@.tmp" "$@"'
 else
 download = $(error Neither wget nor curl found!)
 endif
@@ -338,14 +336,13 @@ HOSTVARS := $(HOSTTOOLS) \
 ifeq ($(DISABLE_CONTRIB_DOWNLOADS),TRUE)
 download_git = $(error Trying to clone $(1) but DISABLE_CONTRIB_DOWNLOADS is TRUE, aborting.)
 else
-download_git = \
-	rm -Rf $(@:.tar.xz=) && \
-	$(GIT) clone $(2:%=--branch %) $(1) $(@:.tar.xz=) && \
-	(cd $(@:.tar.xz=) && $(GIT) checkout $(3:%= %)) && \
-	(test -z "$(4)" && rm -Rf $(@:%.tar.xz=%)/.git) || true && \
-	(cd $(dir $@) && \
-	tar cJ $(notdir $(@:.tar.xz=))) > $@ && \
-	rm -Rf $(@:.tar.xz=)
+download_git = flock "$@.lock" sh -c "\
+  rm -Rf '$(@:.tar.xz=)' && \
+  $(GIT) clone $(2:%=--branch '%') '$(1)' '$(@:.tar.xz=)' && \
+  (cd '$(@:.tar.xz=)' && $(GIT) checkout $(3:%= '%')) && \
+  (test -z '$(4)' && rm -Rf $(@:%.tar.xz='%')/.git) || true && \
+  (cd '$(dir $@)' && tar cJ '$(notdir $(@:.tar.xz=))') > '$@' && \
+  rm -Rf '$(@:.tar.xz=)'"
 endif
 
 checksum = \