How can I find the complete path of the INPUT (r_in_name) and OUTPUT (r_out_name) rasters for the gdal datasets in the following code:

    from qgis.processing import alg
    from qgis.core import QgsFeature, QgsFeatureSink
    import numpy as np
    from osgeo import gdal, gdal_array, osr
    @alg(name="quantilizearaster", label=alg.tr("Quantilize a raster)"), group="rastertools", group_label=alg.tr("Raster Tools"))
    @alg.input(type=alg.RASTER_LAYER, name="INPUT", label="Input layer")
    @alg.input(type=alg.RASTER_LAYER, name="OUTPUT", label="Output layer")
    def quantilize(instance, parameters, context, feedback, inputs):
        """
        This algorithm takes an INPUT raster and quantilize its values in five classes; result is a quantilized OUTPUT raster.
        """
    
    source = instance.parameterAsRasterLayer(parameters, "INPUT", context)
    output_raster = instance.parameterAsRasterLayer(parameters, "OUTPUT", context)
    
    r_in_name =   # r_in_name must be a string of the complete path to the INPUT raster, including its file name (*.tif)
    r_out_name =  # r_out_name may be a temporary OUTPUT raster file
        
 
    dataset = gdal.Open(r_in_name)    
    band = dataset.GetRasterBand(1)
    nodata = band.GetNoDataValue()
    array = dataset.ReadAsArray()

    new_array = array
    nan_array = array

    nan_array[array == nodata] = np.nan

    percentile_80 = np.nanpercentile(nan_array, 80)
    percentile_60 = np.nanpercentile(nan_array, 60)
    percentile_40 = np.nanpercentile(nan_array, 40)
    percentile_20 = np.nanpercentile(nan_array, 20)
    percentile_0 = np.nanpercentile(nan_array, 0)

    for i, v in enumerate(new_array):
        for j, element in enumerate(v):
            if element > percentile_0 and element <= percentile_20:
                new_array[i,j] = 1
            if element > percentile_20 and element <= percentile_40:
                new_array[i,j] = 2
            if element > percentile_40 and element <= percentile_60:
                new_array[i,j] = 3
            if element > percentile_60 and element <= percentile_80:
                new_array[i,j] = 4
            if element > percentile_80:
                new_array[i,j] = 5

    new_array[ new_array != new_array ] = nodata

    geotransform = dataset.GetGeoTransform()
    wkt = dataset.GetProjection()

    # Create gtif file
    
    driver = gdal.GetDriverByName("GTiff")
    output_file = r_out_name  # r_out_name may be a temporary OUTPUT raster file

    dst_ds = driver.Create(output_file,
                           band.XSize,
                           band.YSize,
                           1,
                           gdal.GDT_Int16)

    #writting output raster
    dst_ds.GetRasterBand(1).WriteArray( new_array )
    #setting nodata value
    dst_ds.GetRasterBand(1).SetNoDataValue(nodata)
    #setting extension of output raster
    # top left x, w-e pixel resolution, rotation, top left y, rotation, n-s pixel resolution
    dst_ds.SetGeoTransform(geotransform)
    # setting spatial reference of output raster
    srs = osr.SpatialReference()
    srs.ImportFromWkt(wkt)
    dst_ds.SetProjection( srs.ExportToWkt() )
    #Close output raster dataset

    dataset = None
    dst_ds = None 

    return