0eb6caa076
Any attempt to use open(2) to open a socket file now fails with EOPNOTSUPP, as is common and in the process of being standardized. The behavior and error code is now tested in test56. Any attempt to open a file of which the type is not known to VFS (e.g., as a result of bogus file system contents) now fails with EIO. For now, this is a safety feature, to prevent VFS tripping over such types in unchecked cases. In the future, a proper VFS code audit should determine whether we can lift this restriction again, although it does not seem particularly useful to be able to open files of unknown types anyway. Another error code may be assigned to this case later, too. Change-Id: Ib4cb4341eec954f0448fe469ecf28bd78edebde2