libxl: correct error path in libxl_userdata_retrieve
Firstly, if libxl_read_file_contents fails, it doesn't really leave
*data and *datalen_r undefined - it leaves them unchanged. Tighten up
the spec for the benefit of libxl_userdata_retrieve.
Secondly, libxl_userdata_retrieve ignored errors, assuming they were
all ENOENT. Instead it should fail on unexpected errors.
Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
Acked-by: Jim Fehlig <jfehlig@novell.com>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>