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File: libc.info,  Node: Local Namespace Details,  Next: Local Socket Example,  Prev: Local Namespace Concepts,  Up: Local Namespace

16.5.2 Details of Local Namespace
---------------------------------

To create a socket in the local namespace, use the constant 'PF_LOCAL'
as the NAMESPACE argument to 'socket' or 'socketpair'.  This constant is
defined in 'sys/socket.h'.

 -- Macro: int PF_LOCAL
     This designates the local namespace, in which socket addresses are
     local names, and its associated family of protocols.  'PF_Local' is
     the macro used by Posix.1g.

 -- Macro: int PF_UNIX
     This is a synonym for 'PF_LOCAL', for compatibility's sake.

 -- Macro: int PF_FILE
     This is a synonym for 'PF_LOCAL', for compatibility's sake.

   The structure for specifying socket names in the local namespace is
defined in the header file 'sys/un.h':

 -- Data Type: struct sockaddr_un
     This structure is used to specify local namespace socket addresses.
     It has the following members:

     'short int sun_family'
          This identifies the address family or format of the socket
          address.  You should store the value 'AF_LOCAL' to designate
          the local namespace.  *Note Socket Addresses::.

     'char sun_path[108]'
          This is the file name to use.

          *Incomplete:* Why is 108 a magic number?  RMS suggests making
          this a zero-length array and tweaking the following example to
          use 'alloca' to allocate an appropriate amount of storage
          based on the length of the filename.

   You should compute the LENGTH parameter for a socket address in the
local namespace as the sum of the size of the 'sun_family' component and
the string length (_not_ the allocation size!)  of the file name string.
This can be done using the macro 'SUN_LEN':

 -- Macro: int SUN_LEN (_struct sockaddr_un *_ PTR)
     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The macro computes the length of socket address in the local
     namespace.

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