flushq

- remove messages from a queue

Synopsis

#include <sys/stream.h>

void flushq(queue_t *q, int flag);

Interface Level

Architecture independent level 1 (DDI/DKI).

Parameters

q

Pointer to the queue to be flushed.

flag

Valid flag values are:

FLUSHDATA

Flush only data messages (types M_DATA M_DELAY M_PROTO and M_PCPROTO).

FLUSHALL

Flush all messages.

Description

The flushq() function frees messages and their associated data structures by calling freemsg(9F). If the queue's count falls below the low water mark and the queue was blocking an upstream service procedure, the nearest upstream service procedure is enabled.

Context

The flushq() function can be called from user, interrupt, or kernel context.

Examples

Example 1 Using flushq()

This example depicts the canonical flushing code for STREAMS modules. The module has a write service procedure and potentially has messages on the queue. If it receives an M_FLUSH message, and if the FLUSHR bit is on in the first byte of the message (line 10), then the read queue is flushed (line 11). If the FLUSHW bit is on (line 12), then the write queue is flushed (line 13). Then the message is passed along to the next entity in the stream (line 14). See the example for qreply(9F) for the canonical flushing code for drivers.

      1  /*
      2   * Module write-side put procedure.
      3   */
      4  xxxwput(q, mp)
      5      queue_t *q;
      6      mblk_t *mp;
      7  {
      8   switch(mp->b_datap->db_type) {
      9      case M_FLUSH:
     10        if (*mp->b_rptr & FLUSHR)
     11             flushq(RD(q), FLUSHALL);
     12        if (*mp->b_rptr & FLUSHW)
     13             flushq(q, FLUSHALL);
     14        putnext(q, mp);
     15        break;
               . . .
     16   }
     17  }

See Also

flushband(9F), freemsg(9F), putq(9F), qreply(9F)

Writing Device Drivers STREAMS Programming Guide