1 files changed, 44 insertions, 0 deletions
diff --git a/m4/mmap_write.m4 b/m4/mmap_write.m4
new file mode 100644
index 0000000..3352c3a
--- /dev/null
+++ b/m4/mmap_write.m4
@@ -0,0 +1,44 @@
+dnl * If mmap() plays nicely with write()
+AC_DEFUN([DOVECOT_MMAP_WRITE], [
+  AC_CACHE_CHECK([whether shared mmaps get updated by write()s],i_cv_mmap_plays_with_write,[
+    AC_TRY_RUN([
+      #include <stdio.h>
+      #include <sys/types.h>
+      #include <sys/stat.h>
+      #include <unistd.h>
+      #include <fcntl.h>
+      #include <sys/mman.h>
+      #include <string.h>
+      int main() {
+        /* return 0 if we're signed */
+        int f = open("conftest.mmap", O_RDWR|O_CREAT|O_TRUNC, 0600);
+        void *mem;
+        if (f == -1) {
+          perror("open()");
+          return 1;
+        }
+        unlink("conftest.mmap");
+    
+        write(f, "1", 2);
+        mem = mmap(NULL, 2, PROT_READ|PROT_WRITE, MAP_SHARED, f, 0);
+        if (mem == MAP_FAILED) {
+          perror("mmap()");
+          return 1;
+        }
+        strcpy(mem, "2");
+        msync(mem, 2, MS_SYNC);
+        lseek(f, 0, SEEK_SET);
+        write(f, "3", 2);
+      
+        return strcmp(mem, "3") == 0 ? 0 : 1;
+      }
+    ], [
+      i_cv_mmap_plays_with_write=yes
+    ], [
+      i_cv_mmap_plays_with_write=no
+    ])
+  ])
+  if test $i_cv_mmap_plays_with_write = no; then
+    AC_DEFINE(MMAP_CONFLICTS_WRITE,, [Define if shared mmaps don't get updated by write()s])
+  fi
+])