add detection for broken mmap()/write() behavior

contributed by jim_nance@yahoo.com
r=alecf


git-svn-id: svn://10.0.0.236/trunk@49761 18797224-902f-48f8-a5cc-f745e15eee43

mozilla/configure.in

@@ -1700,6 +1700,53 @@ else
    MOZ_NATIVE_NSPR=1
 fi
 
+dnl See if mmap sees writes
+dnl ========================================================
+dnl For cross compiling, just define it as no, which is a safe default
+AC_MSG_CHECKING(if mmap() sees write()s)
+
+changequote(,)
+mmap_test_prog='
+    #include <stdlib.h>
+    #include <unistd.h>
+    #include <sys/mman.h>
+    #include <sys/types.h>
+    #include <sys/stat.h>
+    #include <fcntl.h>
+
+    char fname[] = "conftest.file";
+    char zbuff[1024]; /* Fractional page is probably worst case */
+
+    int main() {
+	char *map;
+	int fd;
+	int i;
+	unlink(fname);
+	fd = open(fname, O_RDWR | O_CREAT, 0660);
+	if(fd<0) return 1;
+	unlink(fname);
+	write(fd, zbuff, sizeof(zbuff));
+	lseek(fd, 0, SEEK_SET);
+	map = (char*)mmap(0, sizeof(zbuff), PROT_READ, MAP_SHARED, fd, 0);
+	if(map==(char*)-1) return 2;
+	for(i=0; fname[i]; i++) {
+	    int rc = write(fd, &fname[i], 1);
+	    if(map[i]!=fname[i]) return 4;
+	}
+	return 0;
+    }
+'
+changequote([,])
+
+AC_TRY_RUN($mmap_test_prog , result="yes", result="no", result="yes")
+
+AC_MSG_RESULT("$result")
+
+if test "$result" = "no"; then
+    AC_DEFINE(MMAP_MISSES_WRITES)
+fi
+
+
 dnl Checks for library functions.
 dnl ========================================================
 AC_PROG_GCC_TRADITIONAL

mozilla/modules/libreg/src/mmapio.c

@@ -117,6 +117,22 @@ PRInt32  mmio_FileWrite(MmioFile *mmio, const char *src, PRInt32 count)
         mmio->needSeek = PR_FALSE;
     }
 
+    /* If this system does not keep mmap() and write() synchronized, we can
+    ** force it to by doing an munmap() when we do a write.  This will
+    ** obviously slow things down but fortunatly we do not do that many
+    ** writes from within mozilla.  Platforms which need this may want to
+    ** use the new USE_BUFFERED_REGISTRY_IO code instead of this code though.
+    */
+#if MMAP_MISSES_WRITES
+    if(mmio->addr && mmio->msize) {
+	PR_ASSERT(mmio->fileMap);
+	PR_MemUnmap(mmio->addr, mmio->msize);
+	PR_CloseFileMap(mmio->fileMap);
+	mmio->addr  = NULL;
+	mmio->msize = 0;
+    }
+#endif
+
     wcode = PR_Write(mmio->fd, src, count);
 
     if(wcode>0) {