deprecate the --mmap option

* src/main.c (main): Deprecate the --mmap option: issue a warning
when it is used.
(usage): Change description.
* doc/grep.texi (Other Options): Document the new behavior.
* NEWS (Changes in behavior): Mention it.

3 files changed, 12 insertions, 2 deletions

diff --git a/NEWS b/NEWS
index 9efb82ab..0fd60390 100644
--- a/NEWS
+++ b/NEWS
@@ -40,6 +40,12 @@ GNU grep NEWS                                    -*- outline -*-
 
   grep now supports color highlighting of matches on MS-Windows.
 
+** Changes in behavior
+
+  Use of the --mmap option now elicits a warning.  It has been a no-op
+  since March of 2010.
+
+
 * Noteworthy changes in release 2.10 (2011-11-16) [stable]
 
 ** Bug fixes
diff --git a/doc/grep.texi b/doc/grep.texi
index 537237f6..5d779c11 100644
--- a/doc/grep.texi
+++ b/doc/grep.texi
@@ -689,7 +689,8 @@ This can cause a performance penalty.
 @item --mmap
 @opindex --mmap
 @cindex memory mapped input
-This option is ignored for backwards compatibility.  It used to read
+This option is deprecated and now elicits a warning, but is otherwise a no-op.
+It used to make @command{grep} read
 input with the @code{mmap} system call, instead of the default @code{read}
 system call.  On modern systems, @code{mmap} would rarely if ever yield
 better performance.
diff --git a/src/main.c b/src/main.c
index a768d367..a738050c 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1465,7 +1465,7 @@ Miscellaneous:\n\
   -v, --invert-match        select non-matching lines\n\
   -V, --version             print version information and exit\n\
       --help                display this help and exit\n\
-      --mmap                ignored for backwards compatibility\n"));
+      --mmap                deprecated no-op; evokes a warning\n"));
       printf (_("\
 \n\
 Output control:\n\
@@ -2121,6 +2121,9 @@ main (int argc, char **argv)
         break;
 
       case MMAP_OPTION:
+        error (0, 0, _("the --mmap option has been a no-op since 2010"));
+        break;
+
       case 0:
         /* long options */
         break;