msgb - Defines a STREAMS message block
#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 );
A pointer to the next message on the queue. A pointer to
the previous message on the queue. A pointer to the next
message block in the message. A pointer to the first
unread data byte in the buffer. A pointer to the first
unwritten data byte in the buffer. A pointer to the datab
structure (data block) that contains the data for the message.
Additional fields that are visible within the kernel.
The fields included and their contents depend on the
kernel configuration.
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: Used internally
by the STREAMS memory allocator. The first byte of the
buffer. The last byte of the buffer, plus one. The number
of message blocks ( struct msgb) that reference this
data block. The message type. Used internally. Padding.
Messages are typed according to the value in the db_type
field in the associated datab structure. Some possible
type values are: The message contains ordinary data. 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
msgb(4)
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