[PATCH v2] grep: remove --mmap

[Paolo Bonzini]

mmap is a bad idea for sequentially accessed file because it will cause
a page fault for every read page.  Just consider it a failed experiment,
and ignore --mmap while accepting it for backwards compatibility.

* configure.ac (AC_FUNC_MMAP): Remove.
* doc/grep.texi (Other options): Say --mmap is ignored.
* src/grep.c (mmap_option): Remove.
(long_options): Do not reference it.
(bufmapped, initial_bufoffset): Remove.
(reset, fillbuf): Remove HAVE_MMAP code.
(grepfile): Remove bufmapped reference.
(usage): Say --mmap is ignored.
---
 configure.ac  |    1 -
 doc/grep.texi |   10 +++----
 src/main.c    |   76 +++++---------------------------------------------------
 3 files changed, 11 insertions(+), 76 deletions(-)

diff --git a/configure.ac b/configure.ac
index 85f1563..474a9ae 100644
--- a/configure.ac
+++ b/configure.ac
@@ -143,7 +143,6 @@ AC_HEADER_DIRENT
 
 dnl Checks for functions.
 AC_FUNC_CLOSEDIR_VOID
-AC_FUNC_MMAP
 
 AC_CHECK_FUNCS_ONCE(isascii iswctype setlocale wcscoll)
 
diff --git a/doc/grep.texi b/doc/grep.texi
index c2a494d..87480de 100644
--- a/doc/grep.texi
+++ b/doc/grep.texi
@@ -667,12 +667,10 @@ This can cause a performance penalty.
 @item --mmap
 @opindex --mmap
 @cindex memory mapped input
-If possible, use the @code{mmap} system call to read input,
-instead of the default @code{read} system call.
-In some situations, @samp{--mmap} yields better performance.
-However, @samp{--mmap} can cause undefined behavior (including core dumps)
-if an input file shrinks while @command{grep} is operating,
-or if an I/O error occurs.
+This option is ignored for backwards compatibility.  It used to read
+input with the @code{mmap} system call, instead of the default @code{read}
+system call.  On modern systems, @samp{--mmap} rarely if ever yields
+better performance.
 
 @item -U
 @itemx --binary
diff --git a/src/main.c b/src/main.c
index e398adc..6c72650 100644
--- a/src/main.c
+++ b/src/main.c
@@ -21,9 +21,6 @@
 #include <config.h>
 #include <sys/types.h>
 #include <sys/stat.h>
-#if defined(HAVE_MMAP)
-# include <sys/mman.h>
-#endif
 #if defined(HAVE_SETRLIMIT)
 # include <sys/time.h>
 # include <sys/resource.h>
@@ -72,9 +69,6 @@ static int show_version;
 /* If nonzero, suppress diagnostics for nonexistent or unreadable files.  */
 static int suppress_errors;
 
-/* If nonzero, use mmap if possible.  */
-static int mmap_option;
-
 /* If nonzero, use color markers.  */
 static int color_option;
 
@@ -283,7 +277,8 @@ enum
   LINE_BUFFERED_OPTION,
   LABEL_OPTION,
   EXCLUDE_DIRECTORY_OPTION,
-  GROUP_SEPARATOR_OPTION
+  GROUP_SEPARATOR_OPTION,
+  MMAP_OPTION
 };
 
 /* Long options equivalences. */
@@ -320,7 +315,9 @@ static struct option const long_options[] =
   {"line-number", no_argument, NULL, 'n'},
   {"line-regexp", no_argument, NULL, 'x'},
   {"max-count", required_argument, NULL, 'm'},
-  {"mmap", no_argument, &mmap_option, 1},
+
+  /* FIXME: disabled in Mar 2010; warn towards end of 2011; remove in 2013.  */
+  {"mmap", no_argument, NULL, MMAP_OPTION},
   {"no-filename", no_argument, NULL, 'h'},
   {"no-group-separator", no_argument, NULL, GROUP_SEPARATOR_OPTION},
   {"no-messages", no_argument, NULL, 's'},
@@ -419,13 +416,6 @@ static off_t after_last_match;     /* Pointer after last 
matching line that
                                   would have been output if we were
                                   outputting characters. */
 
-#if defined(HAVE_MMAP)
-static int bufmapped;          /* True if buffer is memory-mapped.  */
-static off_t initial_bufoffset;        /* Initial value of bufoffset. */
-#else
-# define bufmapped 0
-#endif
-
 /* Return VAL aligned to the next multiple of ALIGNMENT.  VAL can be
    an integer or a pointer.  Both args must be free of side effects.  */
 #define ALIGN_TO(val, alignment) \
@@ -464,16 +454,6 @@ reset (int fd, char const *file, struct stats *stats)
              return 0;
            }
        }
-#if defined(HAVE_MMAP)
-      initial_bufoffset = bufoffset;
-      bufmapped = mmap_option && bufoffset % pagesize == 0;
-#endif
-    }
-  else
-    {
-#if defined(HAVE_MMAP)
-      bufmapped = 0;
-#endif
     }
   return 1;
 }
@@ -546,48 +526,6 @@ fillbuf (size_t save, struct stats const *stats)
   readsize = buffer + bufalloc - readbuf;
   readsize -= readsize % pagesize;
 
-#if defined(HAVE_MMAP)
-  if (bufmapped)
-    {
-      size_t mmapsize = readsize;
-
-      /* Don't mmap past the end of the file; some hosts don't allow this.
-        Use `read' on the last page.  */
-      if (stats->stat.st_size - bufoffset < mmapsize)
-       {
-         mmapsize = stats->stat.st_size - bufoffset;
-         mmapsize -= mmapsize % pagesize;
-       }
-
-      if (mmapsize
-         && (mmap ((caddr_t) readbuf, mmapsize,
-                   PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_FIXED,
-                   bufdesc, bufoffset)
-             != (caddr_t) -1))
-       {
-         /* Do not bother to use madvise with MADV_SEQUENTIAL or
-            MADV_WILLNEED on the mmapped memory.  One might think it
-            would help, but it slows us down about 30% on SunOS 4.1.  */
-         fillsize = mmapsize;
-       }
-      else
-       {
-         /* Stop using mmap on this file.  Synchronize the file
-            offset.  Do not warn about mmap failures.  On some hosts
-            (e.g. Solaris 2.5) mmap can fail merely because some
-            other process has an advisory read lock on the file.
-            There's no point alarming the user about this misfeature.  */
-         bufmapped = 0;
-         if (bufoffset != initial_bufoffset
-             && lseek (bufdesc, bufoffset, SEEK_SET) < 0)
-           {
-             error (0, errno, _("lseek failed"));
-             cc = 0;
-           }
-       }
-    }
-#endif /*HAVE_MMAP*/
-
   if (! fillsize)
     {
       ssize_t bytesread;
@@ -1352,7 +1290,7 @@ grepfile (char const *file, struct stats *stats)
       if (! file)
        {
          off_t required_offset = outleft ? bufoffset : after_last_match;
-         if ((bufmapped || required_offset != bufoffset)
+         if (required_offset != bufoffset
              && lseek (desc, required_offset, SEEK_SET) < 0
              && S_ISREG (stats->stat.st_mode))
            error (0, errno, "%s", filename);
@@ -1474,7 +1412,7 @@ 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                use memory-mapped input if possible\n"));
+      --mmap                ignored for backwards compatibility\n"));
       printf (_("\
 \n\
 Output control:\n\
-- 
1.6.6.1