freeb(9f) [xfree86 man page]

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

NAME

       freeb - free a message block

SYNOPSIS

       #include <sys/stream.h>

       void  freeb(mblk_t *bp);

PARAMETERS

       bp	Pointer to the message block to be deallocated. mblk_t is an instance of the  msgb(9S) structure.

INTERFACE LEVEL

       Architecture independent level 1 (DDI/DKI).

DESCRIPTION

       freeb()	deallocates  a message block. If the reference count of the  db_ref member of the  datab(9S) structure is greater than	1, freeb()
       decrements the count. If  db_ref equals	1, it deallocates the message block and the corresponding data block and buffer.

       If the data buffer to be freed was allocated with the  esballoc(9F), the buffer may be a non-STREAMS resource. In  that	case,  the  driver
       must  be notified that the attached data buffer needs to be freed, and run its own freeing routine. To make this process independent of the
       driver used in the stream, freeb() finds the  free_rtn(9S) structure associated with the buffer. The  free_rtn structure contains a pointer
       to  the	driver-dependent  routine, which releases the buffer. Once this is accomplished, freeb() releases the STREAMS resources associated
       with the buffer.

CONTEXT

       freeb() can be called from user or interrupt context.

EXAMPLES

       Example 1: Using freeb()

       See copyb(9F) for an example of using freeb().

SEE ALSO

       allocb(9F), copyb(9F), dupb(9F), esballoc(9F), free_rtn(9S)

       Writing Device Drivers

       STREAMS Programming Guide

SunOS 5.10							    13 Nov 2000 							 freeb(9F)

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

NAME

       esballoc - allocate a message block using a caller-supplied buffer

SYNOPSIS

       #include <sys/stream.h>

       mblk_t *esballoc(uchar *base, size_t size, uint_t pri, frtn_t *fr_rtnp);

INTERFACE LEVEL

       Architecture independent level 1 (DDI/DKI).

PARAMETERS

       base	       Address of user supplied data buffer.

       size	       Number of bytes in data buffer.

       pri	       Priority of allocation request (to be used by  allocb(9F) function, called by  esballoc()).

       fr_rtnp	       Free routine data structure.

DESCRIPTION

       esballoc()  creates  a  STREAMS message and attaches a user-supplied data buffer in place of a STREAMS data buffer. It calls  allocb(9F) to
       get a message and data block header only. The newly allocated message will have both the b_wptr and b_rptr set to the base of  the  buffer.
       As  when  using allocb(9F), the	newly allocated message will have both b_wptr and b_rptr set to the base of the data buffer. The user-sup-
       plied data buffer, pointed to by  base, is used as the data buffer for the message.

       When  freeb(9F) is called to free the message, the driver's message freeing routine (referenced through the  free_rtn structure) is called,
       with appropriate arguments, to free the data buffer.

       The  free_rtn structure includes the following members:

	      void (*free_func)();     /* user's freeing routine */
	      char *free_arg;	       /* arguments to free_func() */

       Instead	of  requiring  a  specific  number  of	arguments, the	free_arg field is defined of type  char *. This way, the driver can pass a
       pointer to a structure if more than one argument is needed.

       The method by which free_func is called is implementation-specific. The module writer must not assume that free_func will or  will  not	be
       called directly from STREAMS utility routines like freeb(9F) which free a message block.

       free_func  must	not  call  another  modules put procedure nor attempt to acquire a private module lock which may be held by another thread
       across a call to a STREAMS utility routine which could free a message block. Otherwise, the possibility for lock recursion and/or  deadlock
       exists.

       free_func must not access any dynamically allocated data structure that might no longer exist when it runs.

RETURN VALUES

       On success, a pointer to the newly allocated message block is returned. On failure,  NULL is returned.

CONTEXT

       esballoc() can be called from user or interrupt context.

SEE ALSO

       allocb(9F), freeb(9F), datab(9S), free_rtn(9S)

       Writing Device Drivers STREAMS Programming Guide

WARNINGS

       The   free_func	must  be  defined  in kernel space, should be declared	void and accept one argument.  It has no user context and must not
       sleep.

SunOS 5.10							    23 Jun 1997 						      esballoc(9F)