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msgb(4)
NAME
  msgb - Defines a STREAMS message block

SYNOPSIS
  #include <sys/stream.h>

  struct msgb(
	  struct msgb *b_next,
	  struct msgb *b_prev,
	  struct msgb *b_cont,
	  unsigned char *b_rptr,
	  unsigned char *b_wptr,
	  struct datab *b_datap,
	  MSG_KERNEL_FIELDS );

PARAMETERS
  b_next
      A pointer to the next message on the queue.

  b_prev
      A pointer to the previous message on the queue.

  b_cont
      A pointer to the next message block in the message.

  b_rptr
      A pointer to the first unread data byte in the buffer.

  b_wptr
      A pointer to the first unwritten data byte in the buffer.

  b_datap
      A pointer to the datab structure (data block) that contains the data
      for the message.

  MSG_KERNEL_FIELDS
      Additional fields that are visible within the kernel.  The fields
      included and their contents depend on the kernel configuration.

DESCRIPTION
  The msgb structure defines a message block.  A message block carries data
  or information in a stream.  A STREAMS message consists of message blocks
  linked through b_cont. Each message block points to a data block
  descriptor, which in turn points to a data buffer.

  The msgb structure is typedefed as mblk_t. The associated data block is
  stored in a datab structure, which is typedefed as dblk_t.

  The datab structure is defined (in sys/stream.h) as:

       struct datab {
	       struct datab *  db_freep;
	       unsigned char * db_base;
	       unsigned char * db_lim;
	       unsigned char   db_ref;
	       unsigned char   db_type;
	       unsigned char   db_class;
	       unsigned char   db_pad[1];
       };

  The datab fields are defined as follows:

  db_freep
      Used internally by the STREAMS memory allocator.

  db_base
      The first byte of the buffer.

  db_lim
      The last byte of the buffer, plus one.

  db_ref
      The number of message blocks ( struct msgb) that reference this data
      block.

  db_type
      The message type.

  db_class
      Used internally.

  db_pade
      Padding.

  Messages are typed according to the value in the db_type  field in the
  associated datab  structure.	Some possible type values are:

  M_DATA
      The message contains ordinary data.

  M_PROTO
      The message contains internal control information and data.

  As part of its support for STREAMS, Tru64 UNIX provides the following
  interfaces for exchanging messages betweens STREAMS modules on the one hand
  and sockets and network protocols on the other:

    ·  mbuf_to_mblk() - Converts an mbuf chain to an mblk chain

    ·  mblk_to_mbuf() - Converts an mblk chain to an mbuf chain

Index for Section 4

Alphabetical listing for M

Top of page