move SK_MMAP_SUPPORT into SkPreConfig, so we can know about its availability

trunk/src/core/SkStream.cpp

Index: trunk/src/core/SkStream.cpp
===================================================================
--- trunk/src/core/SkStream.cpp	(revision 8197)
+++ trunk/src/core/SkStream.cpp	(working copy)
@@ -13,6 +13,14 @@
 #include "SkString.h"
 #include "SkOSFile.h"
 
+#if SK_MMAP_SUPPORT
+    #include <unistd.h>
+    #include <sys/mman.h>
+    #include <fcntl.h>
+    #include <errno.h>
+    #include <unistd.h>
+#endif
+
 SK_DEFINE_INST_COUNT(SkStream)
 SK_DEFINE_INST_COUNT(SkWStream)
 SK_DEFINE_INST_COUNT(SkFILEStream)
@@ -789,3 +797,59 @@
 #endif
     return true;
 }
+
+///////////////////////////////////////////////////////////////////////////////
+///////////////////////////////////////////////////////////////////////////////
+
+static bool mmap_filename(const char path[], void** addrPtr, size_t* sizePtr) {
+#if SK_MMAP_SUPPORT
+    int fd = open(path, O_RDONLY);
+    if (fd < 0) {
+        return false;
+    }
+    
+    off_t offset = lseek(fd, 0, SEEK_END);    // find the file size
+    if (offset == -1) {
+        close(fd);
+        return false;
+    }
+    (void)lseek(fd, 0, SEEK_SET);   // restore file offset to beginning
+    
+    // to avoid a 64bit->32bit warning, I explicitly create a size_t size
+    size_t size = static_cast<size_t>(offset);
+    
+    void* addr = mmap(NULL, size, PROT_READ, MAP_SHARED, fd, 0);
+    close(fd);
+    
+    if (MAP_FAILED == addr) {
+        return false;
+    }
+    
+    *addrPtr = addr;
+    *sizePtr = size;
+    return true;
+#else
+    return false;
+#endif
+}
+
+SkStream* SkStream::NewFromFile(const char path[]) {
+    void* addr;
+    size_t size;
+    if (mmap_filename(path, &addr, &size)) {
+        SkAutoTUnref<SkData> data(SkData::NewFromMMap(addr, size));
+        if (data.get()) {
+            return SkNEW_ARGS(SkMemoryStream, (data.get()));
+        }
+    }
+    
+    // If we get here, then our attempt at using mmap failed, so try normal
+    // file access.
+    SkFILEStream* stream = SkNEW_ARGS(SkFILEStream, (path));
+    if (!stream->isValid()) {
+        stream->unref();
+        stream = NULL;
+    }
+    return stream;
+}
+