MSGPULLUP(9F) Kernel Functions for Drivers MSGPULLUP(9F)

msgpullup, msgpullup_pad — concatenate bytes in a message

#include <sys/stream.h>

mblk_t *
msgpullup(mblk_t *mp, ssize_t len);

mblk_t *
msgpullup_pad(mblk_t *mp, ssize_t len, size_t pad);

Architecture independent level 1 (DDI/DKI).

mp
A pointer to an mblk(9S) structure whose blocks are to be concatenated.
len
The number of bytes to concatenate.
pad
The number of uninitialised bytes which should be inserted before the payload in the returned frame.

The () and () functions concatenate and align the first len data bytes of the message pointed to by mp, copying the data into a new message. msgpullup_pad() allows for the insertion of exactly pad bytes before this copied segment to set up desired alignment of any internal structures. msgpullup() inserts no such padding. Any remaining bytes in the remaining message blocks will be cheaply referenced via dupmsg(9F) and linked onto the new message. The original message is unaltered and a new lead mblk_t will always be allocated for a successful call, regardless of whether mp already has sufficient contiguous data bytes or headroom. If len equals , all data are concatenated.

Allocation of padding bytes can be useful for modules working with network packets. If a driver expects that it (or a subsequent module) will insert additional headers or encapsulation, this can provide sufficient headroom to keep all packet headers within a single mblk_t. This padding can be used by adjusting b_rptr downwards, where db_base (datab(9S)) is the lower bound.

If len bytes of the same message type cannot be found, or the requested padding would cause an overflow, () and () fail and return NULL.

The msgpullup() and msgpullup_pad() functions can be called from user, interrupt, or kernel context.

Upon successful completion, the msgpullup() and msgpullup_pad() functions return a non-NULL pointer to the new message. NULL is returned to indicate an illegal set of parameters or an allocation failure.

srv(9E), allocb(9F), dupmsg(9F), pullupmsg(9F), datab(9S), msgb(9S)

Writing Device Drivers.

STREAMS Programming Guide.

The msgpullup() function is a DKI-compliant replacement for the older pullupmsg(9F) routine. Users are strongly encouraged to use msgpullup() instead of pullupmsg(9F).

March 23, 2026 OmniOS