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esballoc(9f)
esballoc(9F) Kernel Functions esballoc(9F)
NAME
esballoc, desballoc - allocate a message block using a caller-supplied
buffer
SYNOPSIS
#include <sys/stream.h>
mblk_t *esballoc(uchar_t *base, size_t size, uint_t pri,
frtn_t *fr_rtnp);
mblk_t *desballoc(uchar_t *base, size_t size, uint_t pri,
frtn_t *fr_rtnp);
INTERFACE LEVEL
esballoc(): Architecture independent level 1 (DDI/DKI)
desballoc(): Solaris DDI specific (Solaris DDI)
PARAMETERS
base Address of caller-supplied data buffer.
size Number of bytes in data buffer.
pri Priority of the request (no longer used).
fr_rtnp Free routine data structure.
DESCRIPTION
The esballoc() and desballoc() functions operate identically to al‐
locb(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 re‐
leasing 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 desballoc()
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 util‐
ity routine that could free a message block. Finally, free_func rou‐
tines specified using desballoc may run in interrupt context and thus
must only use synchronization primitives that include an interrupt pri‐
ority 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.
RETURN VALUES
On success, a pointer to the newly allocated message block is returned.
On failure, NULL is returned.
CONTEXT
The esballoc() and desballoc() functions can be called from user, in‐
terrupt, or kernel context.
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE TYPEAT‐
TRIBUTE VALUE _ Interface StabilityCommitted
SEE ALSO
allocb(9F), ddi_intr_get_pri(9F), ddi_intr_get_softint_pri(9F),
freeb(9F), datab(9S), free_rtn(9S)
Writing Device Drivers in Oracle Solaris 11.4
STREAMS Programming Guide
Oracle Solaris 11.4 16 Jan 2006 esballoc(9F)