class TDataSetManagerFile: public TDataSetManager

 Main constructor

 Parse the input string and set the init bits accordingly
 Format is
    dir:<datasetdir> [mss:<mss-url>] [opt:<base-options>]
 The <datasetdir> is mandatory.
 See TDataSetManager::ParseInitOpts for the available
 base options.
 The base options are laready initialized by the base constructor

 Returns path of the indicated dataset
 Contains a static TString for result. Copy result before using twice.

 Adds the dataset in the folder of group, user to the list in target

 The unsigned int 'option' is forwarded to GetDataSet and BrowseDataSet.
 Available options (to be .or.ed):
    kPrint          print the dataset content
    kQuotaUpdate    update quotas
    kExport         use export naming

 NB1: options "kPrint", "kQuoatUpdate" and "kExport" are mutually exclusive
 NB2: for options "kPrint" and "kQuotaUpdate" return is null.

 General purpose call to go through the existing datasets.
 If <user> is 0 or "*", act on all datasets for the given <group>.
 If <group> is 0 or "*", act on all datasets.
 Action depends on option; available options:

    kExport         Return a TMap object containing all the information about
                    datasets in the form:
                    { <group>, <map of users> }
                                     |
                             { <map of datasets>, <dataset>}
                    (<dataset> are TFileCollection objects)
    kShowDefault    as kExport with in addition a default selection including
                    the datasets from the current user, the ones from the group
                    and the common ones

    kPrint          print the dataset content; no output is returned
    kQuotaUpdate    update {group, user} quotas; no output is returned

 NB1: options "kPrint", "kQuoatUpdate" and "kExport" are mutually exclusive
 NB2: for options "kPrint" and "kQuoatUpdate" return is null.

 Returns the dataset <dsName> of user <user> in group <group> .
 If checksum is non-zero, it will contain the pointer to a TMD5 sum object
 with the checksum of the file, has to be deleted by the user.
 If option has the bi kReadShort set, the shortobject is read, that does not
 contain the list of files. This is much faster.

 Writes indicated dataset.
 If option has the bit kFileMustExist set, the file must still exist,
 otherwise the new dataset is not written (returns 3 in this case).
 If checksum is non-zero the files current checksum is checked against it,
 if it does not match the file is not written (the function returns 2 in this
 case, if the file has disappeared it is also not written (i.e. checksum
 implies the bit kFileMustExist set in option).
 Returns != 0 for success, 0 for error

 Removes the indicated dataset

 Checks if the indicated dataset exits

 Register a dataset, perfoming quota checkings and verification, if required.
 Fails if a dataset with the same name already exists, unless 'opts'
 contains 'O', in which case the old dataset is overwritten.
 If 'opts' contains 'V' the dataset files are also verified (if the dataset manager
 is configured to allow so).
 If 'opts' contains 'T' the in the dataset object (status bits, meta,...)
 is trusted, i.e. not reset (if the dataset manager is configured to allow so).
 By default the dataset is not verified.
 Returns 0 on success, -1 on failure

 Scans the dataset indicated by <uri> and returns the number of missing files.
 Returns -1 if any failure occurs, >= 0 on success.
 For more details, see documentation of
 ScanDataSet(TFileCollection *dataset, const char *option)

 See documentation of ScanDataSet(TFileCollection *dataset, UInt_t option)

 Updates the information in a dataset by opening all files that are not yet
 marked staged creates metadata for each tree in the opened file

 Available options (to be .or.ed)
   kMaxFiles      process a maximum of 'filesmax' files
   kReopen        opens also files that are marked staged
   kTouch         opens and touches files that are marked staged; implies kReopen

 Return code
   negative in case of error
     -1 dataset not found
     -2 could not write dataset after verification

   positive in case of success
     1 dataset was not changed
     2 dataset was changed

 The number of opened, touched, disappeared files can be retrieved by
 GetNTouchedFiles(), GetNOpenedFiles(), GetNDisapparedFiles()

 Returns all datasets for the <group> and <user> specified by <uri>.
 If <user> is 0, it returns all datasets for the given <group>.
 If <group> is 0, it returns all datasets.
 The returned TMap contains:
    <group> --> <map of users> --> <map of datasets> --> <dataset> (TFileCollection)

 The unsigned int 'option' is forwarded to GetDataSet and BrowseDataSet.
 Available options (to be .or.ed):
    kShowDefault    a default selection is shown that include the ones from
                    the current user, the ones from the group and the common ones
    kPrint          print the dataset content
    kQuotaUpdate    update quotas
    kExport         use export naming

 NB1: options "kPrint", "kQuoatUpdate" and "kExport" are mutually exclusive
 NB2: for options "kPrint" and "kQuoatUpdate" return is null.

 Utility function used in various methods for user dataset upload.

 Removes the indicated dataset

 Checks if the indicated dataset exits

 updates the used space maps