build: add configure --with-external-libev

Problem: libev asserts in ev_epoll.c on macos.

Assertion failed: (("libev: I/O watcher with invalid fd found in epoll_ctl", errno != EBADF && errno != ELOOP && errno != EINVAL)), function epoll_modify, file ev_epoll.c, line 134.

The fact that libev is using epoll, which is not native to macos,
indicates that its configure logic is getting confused by the presence
of the epoll-shim (required for the flux_t handle implementation).

Get around this by adding a configure option --with-external-libev so
we can use the homebrew libev, which is properly configured to use kqueue
instead of epoll.

Fixes flux-framework#6485

configure.ac

@@ -483,9 +483,18 @@ RRA_WITH_SYSTEMD_UNITDIR
 
 
 ##
-# Embedded libev
+# libev
 ##
-m4_include([src/common/libev/libev.m4])
+AC_ARG_WITH([external-libev],
+  AS_HELP_STRING([--with-external-libev], [Use external libev]))
+AS_IF([test "x$with_external_libev" = "xyes"], [
+  AC_SEARCH_LIBS([ev_run], [ev], [], [
+    AC_MSG_ERROR([--with-external-libev requested but external libev not found])
+  ])
+],[
+  m4_include([src/common/libev/libev.m4])
+])
+AM_CONDITIONAL([INTERNAL_LIBEV],[test "x$with_external_libev" != "xyes"])
 
 AC_PKGCONFIG
 

src/common/Makefile.am

@@ -1,7 +1,6 @@
 SUBDIRS = \
 	libtap \
 	libtestutil \
-	libev \
 	libyuarel \
 	libpmi \
 	liblsd \
@@ -30,6 +29,9 @@ SUBDIRS = \
 	libfilemap \
 	libsdexec \
 	libmissing
+if INTERNAL_LIBEV
+SUBDIRS += libev
+endif
 
 AM_CFLAGS = $(WARNING_CFLAGS) $(CODE_COVERAGE_CFLAGS)
 AM_LDFLAGS = $(CODE_COVERAGE_LIBS)
@@ -45,7 +47,6 @@ libflux_internal_la_LIBADD = \
 	$(builddir)/libccan/libccan.la \
 	$(builddir)/libutil/libutil.la \
 	$(builddir)/libidset/libidset.la \
-	$(builddir)/libev/libev.la \
 	$(builddir)/libyuarel/libyuarel.la \
 	$(builddir)/libtomlc99/libtomlc99.la \
 	$(builddir)/libeventlog/libeventlog.la \
@@ -62,6 +63,9 @@ libflux_internal_la_LIBADD = \
 	$(LIBDL) \
 	$(LIBRT) \
 	$(FLUX_SECURITY_LIBS)
+if INTERNAL_LIBEV
+libflux_internal_la_LIBADD += $(builddir)/libev/libev.la
+endif
 libflux_internal_la_LDFLAGS = $(san_ld_zdef_flag)
 
 lib_LTLIBRARIES = libflux-core.la \

src/common/libflux/Makefile.am

@@ -19,6 +19,10 @@ AM_CPPFLAGS = \
 	$(JANSSON_CFLAGS) \
 	$(LIBUUID_CFLAGS)
 
+if INTERNAL_LIBEV
+AM_CPPFLAGS += -I$(top_srcdir)/src/common/libev
+endif
+
 fluxcoreinclude_HEADERS = \
 	flux.h \
 	types.h \

src/common/libflux/reactor.c

@@ -16,10 +16,9 @@
 #include <errno.h>
 #include <stdbool.h>
 #include <fcntl.h>
+#include <ev.h>
 #include <flux/core.h>
 
-#include "src/common/libev/ev.h"
-
 #include "reactor_private.h"
 
 struct flux_reactor {

src/common/libflux/watcher_wrap.c

@@ -14,10 +14,9 @@
 #include "config.h"
 #endif
 #include <assert.h>
+#include <ev.h>
 #include <flux/core.h>
 
-#include "src/common/libev/ev.h"
-
 #include "reactor_private.h"
 #include "watcher_private.h"