Doc updates for work since 4.83

[exim.git] / src / OS / os.h-Linux

diff --git a/src/OS/os.h-Linux b/src/OS/os.h-Linux
index bde5dd7105087b77e7005023323f648ec618b185..3fead17d71d24a26c0664957e2eca3c7939bf986 100644 (file)
--- a/src/OS/os.h-Linux
+++ b/src/OS/os.h-Linux
@@ -1,7 +1,12 @@
-/* $Cambridge: exim/src/OS/os.h-Linux,v 1.7 2007/10/04 13:28:06 tom Exp $ */
-
 /* Exim: OS-specific C header file for Linux */
 
+/* Some old systems we've received bug-reports for have a <limits.h> which
+does not pull in <features.h>.  Best to just pull it in now and have done
+with the issue. */
+
+#include <features.h>
+
+
 #define CRYPT_H
 #define GLIBC_IP_OPTIONS
 #define HAVE_MMAP
@@ -10,10 +15,10 @@
 #define NO_IP_VAR_H
 #define SIG_IGN_WORKS
 
-/* When using the experimental Domainkeys/DKIM extensions, setting
-HAVE_LINUX_SENDFILE can increase performance on outgoing mail a bit.
-Note: With older glibc versions this setting will conflict with the
-_FILE_OFFSET_BITS=64 setting defined as part of the Linux CFLAGS. */
+/* When using the DKIM, setting HAVE_LINUX_SENDFILE can increase
+performance on outgoing mail a bit. Note: With older glibc versions
+this setting will conflict with the _FILE_OFFSET_BITS=64 setting
+defined as part of the Linux CFLAGS. */
 
 /* #define HAVE_LINUX_SENDFILE */
 
@@ -52,4 +57,16 @@ extern struct ip_address_item *os_find_running_interfaces_linux(void);
 
 #endif /* __linux__ */
 
+/* Some folks running "unusual" setups with very old libc environments have
+found that _GNU_SOURCE=1 before <features.h> is not sufficient to define some
+constants needed for 64-bit arithmetic.  If you encounter build errors based
+on LLONG_MIN being undefined and various other escape hatches have not helped,
+then change the 0 to 1 in the next block. */
+
+#if 0
+# define LLONG_MIN LONG_LONG_MIN
+# define LLONG_MAX LONG_LONG_MAX
+#endif
+
+
 /* End */