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(libc.info)Local Namespace Details

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Details of Local Namespace
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   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)
     The macro computes the length of socket address in the local
     namespace.