RangeSync() should work with ROCKSDB_FALLOCATE_PRESENT not set

Summary: Closes https://github.com/facebook/rocksdb/pull/1824

Differential Revision: D4493862

Pulled By: siying

fbshipit-source-id: c168446

util/io_posix.cc

@@ -755,6 +755,7 @@ Status PosixWritableFile::Allocate(uint64_t offset, uint64_t len) {
     return IOError(filename_, errno);
   }
 }
+#endif
 
 Status PosixWritableFile::RangeSync(uint64_t offset, uint64_t nbytes) {
   assert(offset <= std::numeric_limits<off_t>::max());
@@ -770,7 +771,6 @@ Status PosixWritableFile::RangeSync(uint64_t offset, uint64_t nbytes) {
 size_t PosixWritableFile::GetUniqueId(char* id, size_t max_size) const {
   return PosixHelper::GetUniqueIdFromFile(fd_, id, max_size);
 }
-#endif
 
 /*
  * PosixRandomRWFile

util/io_posix.h

@@ -113,9 +113,9 @@ class PosixWritableFile : public WritableFile {
   virtual Status InvalidateCache(size_t offset, size_t length) override;
 #ifdef ROCKSDB_FALLOCATE_PRESENT
   virtual Status Allocate(uint64_t offset, uint64_t len) override;
+#endif
   virtual Status RangeSync(uint64_t offset, uint64_t nbytes) override;
   virtual size_t GetUniqueId(char* id, size_t max_size) const override;
-#endif
 };
 
 // mmap() based random-access