Richard W.M. Jones wrote:
> On Thu, Nov 24, 2011 at 03:01:03PM +0000, Paul Howarth wrote:
>> http://marc.info/?l=pptpclient-devel&m=132102054518031
>
> This is indeed rather unexpected behaviour of make!
>
> BTW I think your patch is incomplete, since it will create an
> incomplete config.h if the disk runs out of space. I think this would
> be better, and should also avoid the parallel make problem:
>
> config.h:
> echo "/* text added by Makefile target config.h */" > $@-t
> echo "#define PPTP_LINUX_VERSION \"$(VERSION)$(RELEASE)\"" >> $@-t
> echo "#define PPPD_BINARY \"$(PPPD)\"" >> $@-t
> echo "#define IP_BINARY \"$(IP)\"" >> $@-t
> mv $@-t $@
Yes, that is better and does solve the problem.
Here's a good rule I've been following since I was first burned by this:
"never redirect directly to a Makefile target". (where "target" means $@
or any literal that is equivalent). That means redirect output to a
temporary file like Rich did above, and only when that process is known
to have succeeded do you rename the temporary file to $@.
However, I would volunteer some additional suggestions:
- use a {...} group (cheaper than a (...) subshell) so we redirect only once;
that reduces the duplication of the "$@-t", and eliminates the dichotomy
of the initial "> $@-t", while all subsequent ones are ">> $@-t".
- use outer single quotes so you don't have to backslash-escape the
inner double quote chars. less syntax is more maintainable.
- make the file read-only, so it is clearer that it is generated,
and thus harder to change accidentally. The only down-side to
this part is that you then have to be careful to remove any
preexisting $@ or $@-t, since redirecting onto a read-only file
will often fail.
config.h:
rm -f $@ $@-t; \
{ \
echo '/* text added by Makefile target config.h */'; \
echo '#define PPTP_LINUX_VERSION "$(VERSION)$(RELEASE)"'; \
echo '#define PPPD_BINARY "$(PPPD)"'; \
echo '#define IP_BINARY "$(IP)"'; \
} > $@-t && chmod a-w $@-t && mv $@-t $@
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