• db: A mongoc_database_t.
• opts: A bson_t or NULL
• read_prefs: A mongoc_read_prefs_t used for read operations or NULL to inherit read preferences from db.
• error: A bson_error_t or NULL.
opts may be NULL or a BSON document with additional command options:
• bucketName: A UTF-8 string used as the prefix to the GridFS "chunks" and "files" collections. Defaults
to "fs". The bucket name, together with the database and suffix collections must not exceed 120
characters. See the manual for themaxnamespacelength.
• chunkSizeBytes: An int32 representing the chunk size. Defaults to 255KB.
• writeConcern: Construct a mongoc_write_concern_t and use mongoc_write_concern_append() to add the write
concern to opts. See the example code for mongoc_client_write_command_with_opts().
• readConcern: Construct a mongoc_read_concern_t and use mongoc_read_concern_append() to add the read
concern to opts. See the example code for mongoc_client_read_command_with_opts(). Read concern requires
MongoDB 3.2 or later, otherwise an error is returned.