dupb(D3)
dupb - duplicate a message block
As shipped in IRIX 6.5. First release of IRIX 6.5.
NAME dupb - duplicate a message block SYNOPSIS #include <sys/stream.h> #include <sys/ddi.h> mblk_t *dupb(mblk_t *bp); Arguments bp Pointer to the message block to be duplicated. DESCRIPTION dupb creates a new message block structure that references the same data block that is referenced by bp. Unlike copyb(D3), dupb does not copy the information in the data block, but creates a new structure to point to it. Return Values On success, dupb returns a pointer to the new message block. On failure, it returns a NULL pointer. USAGE The following figure shows how the db_ref field of the data block structure has been changed from 1 to 2, reflecting the increase in the number of references to the data block. The new message block contains the same information as the first. Note that b_rptr and b_wptr are copied from bp, and that db_ref is incremented. ______ | | ___ . . . . . . . . . . . . . . . . . . . . . . . . | ______ | ______ . . . . . . . . . . . . . . . . . . . . . . . . | ______ | ______ | nbp=dupb(bp); | __________________________ __________________ Before After db_base db_ref (2) | _________ | _________ | _________ | _________ db_base db_ref (1) bp | ______ | ______ b_datap b_rptr b_wptr | ______ | ______ b_datap b_rptr b_wptr | ______ | ______ b_datap b_rptr b_wptr _________ | nbp ________ | _________ | ________ | bp Level Base or Interrupt. Synchronization Constraints Does not sleep. Driver-defined basic locks, read/write locks, and sleep locks may be held across calls to this function. REFERENCES copyb(D3), dupmsg(D3), datab(D4), msgb(D4)