NAME

esballoc, desballoc esballoca, desballoca - 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);

#include <sys/strsubr.h>

mblk_t *esballoca(uchar_t *base, size_t size, uint_t pri,


     frtn_t *fr_rtnp);

mblk_t *desballoca(uchar_t *base, size_t size, uint_t pri,


     frtn_t *fr_rtnp);

mblk_t *esballoc_wait(uchar_t *base, size_t size, uint_t pri,


     frtn_t *fr_rtnp);

mblk_t *esballoca_wait(uchar_t *base, size_t size, uint_t pri,


     frtn_t *fr_rtnp);

INTERFACE LEVEL

esballoc(): Architecture independent level 1 (DDI/DKI)

esballoca(): illumos DDI specific (illumos DDI)
desballoc(): illumos DDI specific (illumos DDI)
desballoca(): illumos DDI specific (illumos DDI)



esballoc_wait(): Volatile (private DDI function)
esballoca_wait(): Volatile (private DDI function)

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(), esballoca(), desballoc() and desballoca() 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. Note that the address of the free_rtn(9S) structure passed to esballoc() is used when the returned mblk/dblk pair is freed, and must remain valid until then.

If esballoc() or esballoca() was used, then free_func will be called asynchronously at some point after the message is no longer referenced. If desballoc() or desballoca() 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 dynamically allocated data structures that could be freed before or during its execution. In addition, because messages allocated with desballoc() or desballoca() 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() or desballoca() 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_softint_pri(9F). If any of these restrictions are not followed, the possibility of lock recursion or deadlock exists.

The variants ending with 'a' (esballoca() or desballoca() add an "extra" ref to the dblk returned, also setting an internal flag so that freeb(9F) handles the extra ref. The point of this extra ref is so that any streams code handling this data block knows that the data should not be modified without taking a copy. This is used by callers sending external buffers that must not be modified.

The variants ending with "_wait" do a sleeping allocation, where the ordinary esballoc() functions can return NULL when the system is low on free memory.

RETURN VALUES

On success, a pointer to the newly allocated message block is returned. On failure, esballoc(), esballoca(), desballoc() and desballoca() return NULL. The functions esballoc_wait() and esballoca_wait() do not return errors, and instead sleep until memory is available.

CONTEXT

The esballoc(), esballoca(), desballoc() and desballoca() functions can be called from user, interrupt, or kernel context. The functions esballoc_wait() and esballoca_wait() can block and should not be called from interrupt context.

ATTRIBUTES

See attributes(7) for descriptions of the following attributes:

ATTRIBUTE TYPE	ATTRIBUTE VALUE
Interface Stability	Committed
Interface Stability	Volatile