On Mon, May 11, 2015 at 10:05:28AM +0200, Karel Zak wrote: > On Sun, May 10, 2015 at 01:38:08PM -0700, Isaac Dunham wrote: > > On Tue, May 05, 2015 at 11:37:33AM +0100, Pádraig Brady wrote: > > > On 04/05/15 04:51, Mike Frysinger wrote: > > > > From: Mike Frysinger <vapier@xxxxxxxxxxxx> > > > > > > > > The symlink generation tries to write to the sys-utils/ subdir but does > > > > not make sure that dir exists. This can sometimes lead to parallel build > > > > failures when building out-of-tree > > > > > > > $(SETARCH_MAN_LINKS): > > > > + $(AM_V_at) test -d $(dir $@) || mkdir -p $(dir $@) > > > > $(AM_V_GEN)echo ".so man8/setarch.8" > $@ > > > > > > > > install-exec-hook-setarch: > > > > > > The `test -d ... ||` bit is racy and redundant I think > > > > Racy, yes, but no more so than "mkdir -p $DIR && install $FILE $DIR": > > it's an inherent limitation of shell scripts. You mean racy as in multiple mkdir -p invocations could happen? A C implementation could shorten the window for the race (because mkdir(2) would directly follow stat(2), rather than delayed by fork/exec/dynamic linker startup). Or handle EEXISTS specially and test again for existance. You could do most of that in shell, but it would make the code a mess. > > Redundant, certainly: mkdir -p $DIR is required to succeed if $DIR is > > a preexisting directory (though it will fail if part of the path is a > > regular file). > > It seems that 'test || mkdir' is nothing unusual in makefiles. The > problem is "mkdir -p" portability (at least from autotools point of > view :-), it seems that the proper way is to use > > @$(MKDIR_P) $(dir $@) > > rather than directly call mkdir. The test || mkdir idiom also has a performance benefit: test is a shell builtin in most/all shells. stat(2) is a lot faster than fork / exec / process startup. (For portable build systems, this is a huge deal on cygwin compared to anything else, because the overhead of running a binary is huge there.) Anyway, if checking for existence is going to happen often, then it's worth doing test || mkdir, rather than relying on GNU mkdir -p. -- #define X(x,y) x##y Peter Cordes ; e-mail: X(peter@cor , des.ca) "The gods confound the man who first found out how to distinguish the hours! Confound him, too, who in this place set up a sundial, to cut and hack my day so wretchedly into small pieces!" -- Plautus, 200 BC -- To unsubscribe from this list: send the line "unsubscribe util-linux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
