Architecture independent level 1 (DDI/DKI)

A STREAMS driver or module consists of two queue structures, one for upstream processing (read) and one for downstream processing (write). This structure is the major building block of a stream. It contains pointers to the processing procedures, pointers to the next and previous queues in the stream, flow control parameters, and a pointer defining the position of its messages on the STREAMS scheduler list.

The queue structure is defined as type queue_t.

struct      qinit*q_qinfo;      /* module or driver entry points */
struct      msgb*q_first;       /* first message in queue */
struct      msgb*q_last;        /* last message in queue */
struct      queue*q_next;       /* next queue in stream */
struct      queue*q_link;       /* to next queue for scheduling*/
void        *q_ptr;             /* pointer to private data structure */
size_t      q_count;            /* approximate size of message queue */
uint_t      q_flag;             /* status of queue */
ssize_t     q_minpsz;           /* smallest packet accepted by QUEUE*/
ssize_t     q_maxpsz;           /*largest packet accepted by QUEUE */
size_t      q_hiwat;            /* high water mark */
size_t      q_lowat;            /* low water mark */

Valid flags are as follows:

QENAB

Queue is already enabled to run.

QWANTR

Someone wants to read queue.

QWANTW

Someone wants to write to queue.

QFULL

Queue is considered full.

QREADR

This is the reader (first) queue.

QUSE

This queue is in use (allocation).

QNOENB

Do not enable queue by way of putq().

strqget(9F), strqset(9F), module_info(9S), msgb(9S), qinit(9S), streamtab(9S)

Writing Device Drivers

STREAMS Programming Guide