Had to open data source read-only.
INFO: Open of `/home/mku/dev/cpp/qgis/QGIS/python/plugins/processing/tests/testdata/lines.gml'
      using driver `GML' successful.

Layer name: lines
Geometry: Line String
Feature Count: 7
Extent: (-1.000000, -3.000000) - (11.000000, 5.000000)
Layer SRS WKT:
GEOGCS["WGS 84",
    DATUM["WGS_1984",
        SPHEROID["WGS 84",6378137,298.257223563,
            AUTHORITY["EPSG","7030"]],
        AUTHORITY["EPSG","6326"]],
    PRIMEM["Greenwich",0,
        AUTHORITY["EPSG","8901"]],
    UNIT["degree",0.0174532925199433,
        AUTHORITY["EPSG","9122"]],
    AUTHORITY["EPSG","4326"]]
fid: String (0.0) NOT NULL