esballoc, desballoc - allocate a message block using a caller-supplied
mblk_t *esballoc(uchar_t *base, size_t size, uint_t pri,
mblk_t *desballoc(uchar_t *base, size_t size, uint_t pri,
INTERFACE LEVELesballoc(): Architecture independent level 1 (DDI/DKI)
desballoc(): Solaris DDI specific (Solaris DDI)
Address of caller-supplied data buffer.
Number of bytes in data buffer.
Priority of the request (no longer used).
Free routine data structure.
The esballoc() and desballoc() functions operate identically to
allocb(9F), except that the data buffer to associate with the message
is specified by the caller. The allocated message will have both the
b_wptr and b_rptr set to the supplied data buffer starting at base.
Only the buffer itself can be specified by the caller. The message
block and data block header are allocated as if by allocb(9F).
When freeb(9F) is called to free the message, the driver's message-
freeing routine, referenced through the free_rtn(9S) structure, is
called with appropriate arguments to free the data buffer.
The free_rtn(9S) structure includes the following members:
void (*free_func)(); /* caller's freeing routine */
caddr_t free_arg; /* argument to free_func() */
Instead of requiring a specific number of arguments, the free_arg field
is defined of type caddr_t. This way, the driver can pass a pointer to
a structure if more than one argument is needed.
If esballoc() was used, then free_func will be called asynchronously at
some point after the message is no longer referenced. If desballoc()
was used, then free_func will be called synchronously by the thread
releasing the final reference. See freeb(9F).
The free_func routine must not sleep, and must not access any dynami‐
cally allocated data structures that could be freed before or during
its execution. In addition, because messages allocated with desbal‐
loc() are freed in the context of the caller, free_func must not call
another module's put procedure, or attempt to acquire a private module
lock which might be held by another thread across a call to a STREAMS
utility routine that could free a message block. Finally, free_func
routines specified using desballoc may run in interrupt context and
thus must only use synchronization primitives that include an interrupt
priority returned from ddi_intr_get_pri(9F) or ddi_intr_get_soft‐
int_pri(9F). If any of these restrictions are not followed, the possi‐
bility of lock recursion or deadlock exists.
On success, a pointer to the newly allocated message block is returned.
On failure, NULL is returned.
The esballoc() and desballoc() functions can be called from user,
interrupt, or kernel context.
See attributes(5) for descriptions of the following attributes:
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
│Interface Stability │ Committed │
SEE ALSOallocb(9F), ddi_intr_get_pri(9F), ddi_intr_get_softint_pri(9F),
freeb(9F), datab(9S), free_rtn(9S)
Writing Device Drivers
STREAMS Programming Guide
Jan 16, 2006 ESBALLOC(9F)