Merge branch 'kb/use-nsec-doc'

Clarify in the Makefile a guideline to decide use of USE_NSEC.

* kb/use-nsec-doc:
Makefile / racy-git.txt: clarify USE_NSEC prerequisites

diff --combined Makefile
index 149f1c7c3740e9513cc2e35f590b987bbee6f0a4,46d181a7d37d3e448675a68b5eb87baf5f1e982e..895f002869045288dfc6298e596c020aa4bc8efd
--- 1/Makefile
--- 2/Makefile
+++ b/Makefile
@@@ -217,10 -217,11 +217,11 @@@ all:
  # as the compiler can crash (http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49299)
  #
  # Define USE_NSEC below if you want git to care about sub-second file mtimes
- # and ctimes. Note that you need recent glibc (at least 2.2.4) for this, and
- # it will BREAK YOUR LOCAL DIFFS! show-diff and anything using it will likely
- # randomly break unless your underlying filesystem supports those sub-second
- # times (my ext3 doesn't).
+ # and ctimes. Note that you need recent glibc (at least 2.2.4) for this. On
+ # Linux, kernel 2.6.11 or newer is required for reliable sub-second file times
+ # on file systems with exactly 1 ns or 1 s resolution. If you intend to use Git
+ # on other file systems (e.g. CEPH, CIFS, NTFS, UDF), don't enable USE_NSEC. See
+ # Documentation/technical/racy-git.txt for details.
  #
  # Define USE_ST_TIMESPEC if your "struct stat" uses "st_ctimespec" instead of
  # "st_ctim"
@@@ -1747,7 -1748,7 +1748,7 @@@ $(SCRIPT_PERL_GEN): perl/perl.ma
  perl/perl.mak: perl/PM.stamp
  
  perl/PM.stamp: FORCE
 -      $(QUIET_GEN)$(FIND) perl -type f -name '*.pm' | sort >$@+ && \
 +      @$(FIND) perl -type f -name '*.pm' | sort >$@+ && \
        { cmp $@+ $@ >/dev/null 2>/dev/null || mv $@+ $@; } && \
        $(RM) $@+
  
@@@ -1784,7 -1785,7 +1785,7 @@@ GIT-PERL-DEFINES: FORC
  gitweb:
        $(QUIET_SUBDIR0)gitweb $(QUIET_SUBDIR1) all
  
 -git-instaweb: git-instaweb.sh gitweb GIT-SCRIPT-DEFINES
 +git-instaweb: git-instaweb.sh GIT-SCRIPT-DEFINES
        $(QUIET_GEN)$(cmd_munge_script) && \
        chmod +x $@+ && \
        mv $@+ $@
@@@ -2103,47 -2104,46 +2104,47 @@@ GIT-LDFLAGS: FORC
  # that runs GIT-BUILD-OPTIONS, and then again to protect it
  # and the first level quoting from the shell that runs "echo".
  GIT-BUILD-OPTIONS: FORCE
 -      @echo SHELL_PATH=\''$(subst ','\'',$(SHELL_PATH_SQ))'\' >$@
 -      @echo PERL_PATH=\''$(subst ','\'',$(PERL_PATH_SQ))'\' >>$@
 -      @echo DIFF=\''$(subst ','\'',$(subst ','\'',$(DIFF)))'\' >>$@
 -      @echo PYTHON_PATH=\''$(subst ','\'',$(PYTHON_PATH_SQ))'\' >>$@
 -      @echo TAR=\''$(subst ','\'',$(subst ','\'',$(TAR)))'\' >>$@
 -      @echo NO_CURL=\''$(subst ','\'',$(subst ','\'',$(NO_CURL)))'\' >>$@
 -      @echo NO_EXPAT=\''$(subst ','\'',$(subst ','\'',$(NO_EXPAT)))'\' >>$@
 -      @echo USE_LIBPCRE=\''$(subst ','\'',$(subst ','\'',$(USE_LIBPCRE)))'\' >>$@
 -      @echo NO_PERL=\''$(subst ','\'',$(subst ','\'',$(NO_PERL)))'\' >>$@
 -      @echo NO_PYTHON=\''$(subst ','\'',$(subst ','\'',$(NO_PYTHON)))'\' >>$@
 -      @echo NO_UNIX_SOCKETS=\''$(subst ','\'',$(subst ','\'',$(NO_UNIX_SOCKETS)))'\' >>$@
 +      @echo SHELL_PATH=\''$(subst ','\'',$(SHELL_PATH_SQ))'\' >$@+
 +      @echo PERL_PATH=\''$(subst ','\'',$(PERL_PATH_SQ))'\' >>$@+
 +      @echo DIFF=\''$(subst ','\'',$(subst ','\'',$(DIFF)))'\' >>$@+
 +      @echo PYTHON_PATH=\''$(subst ','\'',$(PYTHON_PATH_SQ))'\' >>$@+
 +      @echo TAR=\''$(subst ','\'',$(subst ','\'',$(TAR)))'\' >>$@+
 +      @echo NO_CURL=\''$(subst ','\'',$(subst ','\'',$(NO_CURL)))'\' >>$@+
 +      @echo NO_EXPAT=\''$(subst ','\'',$(subst ','\'',$(NO_EXPAT)))'\' >>$@+
 +      @echo USE_LIBPCRE=\''$(subst ','\'',$(subst ','\'',$(USE_LIBPCRE)))'\' >>$@+
 +      @echo NO_PERL=\''$(subst ','\'',$(subst ','\'',$(NO_PERL)))'\' >>$@+
 +      @echo NO_PYTHON=\''$(subst ','\'',$(subst ','\'',$(NO_PYTHON)))'\' >>$@+
 +      @echo NO_UNIX_SOCKETS=\''$(subst ','\'',$(subst ','\'',$(NO_UNIX_SOCKETS)))'\' >>$@+
  ifdef TEST_OUTPUT_DIRECTORY
 -      @echo TEST_OUTPUT_DIRECTORY=\''$(subst ','\'',$(subst ','\'',$(TEST_OUTPUT_DIRECTORY)))'\' >>$@
 +      @echo TEST_OUTPUT_DIRECTORY=\''$(subst ','\'',$(subst ','\'',$(TEST_OUTPUT_DIRECTORY)))'\' >>$@+
  endif
  ifdef GIT_TEST_OPTS
 -      @echo GIT_TEST_OPTS=\''$(subst ','\'',$(subst ','\'',$(GIT_TEST_OPTS)))'\' >>$@
 +      @echo GIT_TEST_OPTS=\''$(subst ','\'',$(subst ','\'',$(GIT_TEST_OPTS)))'\' >>$@+
  endif
  ifdef GIT_TEST_CMP
 -      @echo GIT_TEST_CMP=\''$(subst ','\'',$(subst ','\'',$(GIT_TEST_CMP)))'\' >>$@
 +      @echo GIT_TEST_CMP=\''$(subst ','\'',$(subst ','\'',$(GIT_TEST_CMP)))'\' >>$@+
  endif
  ifdef GIT_TEST_CMP_USE_COPIED_CONTEXT
 -      @echo GIT_TEST_CMP_USE_COPIED_CONTEXT=YesPlease >>$@
 +      @echo GIT_TEST_CMP_USE_COPIED_CONTEXT=YesPlease >>$@+
  endif
 -      @echo NO_GETTEXT=\''$(subst ','\'',$(subst ','\'',$(NO_GETTEXT)))'\' >>$@
 -      @echo GETTEXT_POISON=\''$(subst ','\'',$(subst ','\'',$(GETTEXT_POISON)))'\' >>$@
 +      @echo NO_GETTEXT=\''$(subst ','\'',$(subst ','\'',$(NO_GETTEXT)))'\' >>$@+
 +      @echo GETTEXT_POISON=\''$(subst ','\'',$(subst ','\'',$(GETTEXT_POISON)))'\' >>$@+
  ifdef GIT_PERF_REPEAT_COUNT
 -      @echo GIT_PERF_REPEAT_COUNT=\''$(subst ','\'',$(subst ','\'',$(GIT_PERF_REPEAT_COUNT)))'\' >>$@
 +      @echo GIT_PERF_REPEAT_COUNT=\''$(subst ','\'',$(subst ','\'',$(GIT_PERF_REPEAT_COUNT)))'\' >>$@+
  endif
  ifdef GIT_PERF_REPO
 -      @echo GIT_PERF_REPO=\''$(subst ','\'',$(subst ','\'',$(GIT_PERF_REPO)))'\' >>$@
 +      @echo GIT_PERF_REPO=\''$(subst ','\'',$(subst ','\'',$(GIT_PERF_REPO)))'\' >>$@+
  endif
  ifdef GIT_PERF_LARGE_REPO
 -      @echo GIT_PERF_LARGE_REPO=\''$(subst ','\'',$(subst ','\'',$(GIT_PERF_LARGE_REPO)))'\' >>$@
 +      @echo GIT_PERF_LARGE_REPO=\''$(subst ','\'',$(subst ','\'',$(GIT_PERF_LARGE_REPO)))'\' >>$@+
  endif
  ifdef GIT_PERF_MAKE_OPTS
 -      @echo GIT_PERF_MAKE_OPTS=\''$(subst ','\'',$(subst ','\'',$(GIT_PERF_MAKE_OPTS)))'\' >>$@
 +      @echo GIT_PERF_MAKE_OPTS=\''$(subst ','\'',$(subst ','\'',$(GIT_PERF_MAKE_OPTS)))'\' >>$@+
  endif
  ifdef TEST_GIT_INDEX_VERSION
 -      @echo TEST_GIT_INDEX_VERSION=\''$(subst ','\'',$(subst ','\'',$(TEST_GIT_INDEX_VERSION)))'\' >>$@
 +      @echo TEST_GIT_INDEX_VERSION=\''$(subst ','\'',$(subst ','\'',$(TEST_GIT_INDEX_VERSION)))'\' >>$@+
  endif
 +      @if cmp $@+ $@ >/dev/null 2>&1; then $(RM) $@+; else mv $@+ $@; fi
  
  ### Detect Python interpreter path changes
  ifndef NO_PYTHON