private long getPos() throws IOException {
      return ((HFileWriterImpl) writer).getPos();
    }
Creates an HFile.Writer that also write helpful meta data.
@param fs                     file system to write to
@param path                   file name to create
@param conf                   user configuration
@param bloomType              bloom filter setting
@param maxKeys                the expected maximum number of keys to be added. Was used for
                              Bloom filter size in {@link HFile} format version 1.
@param favoredNodes           an array of favored nodes or possibly null
@param fileContext            The HFile context
@param shouldDropCacheBehind  Drop pages written to page cache after writing the store file.
@param compactedFilesSupplier Returns the {@link HStore} compacted files which not archived
@throws IOException problem writing to FS
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/StoreFileWriter.java