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Full Discussion: Dynamic Memory Allocation
Top Forums Programming Dynamic Memory Allocation Post 302532137 by tene on Monday 20th of June 2011 03:59:33 AM
Old 06-20-2011
Dynamic Memory Allocation
Hello Guys

I have a small confusion in the dynamic memory allocation concept.
If we declare a pointer say a char pointer, we need to allocate adequate memory space.

Code:
char* str = (char*)malloc(20*sizeof(char));
str = "This is a string";


But this will also work.

Code:
char* str = "This is a string";

So in which case do we have to allocate memory space?
 

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LEARN ABOUT SUNOS

ddi_iopb_free

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

NAME

       ddi_iopb_alloc, ddi_iopb_free - allocate and free non-sequentially accessed memory

SYNOPSIS

       #include <sys/ddi.h>
       #include <sys/sunddi.h>

       int ddi_iopb_alloc(dev_info_t *dip, ddi_dma_lim_t *limits, uint_t length, caddr_t *iopbp);

       void ddi_iopb_free(caddr_t iopb);

INTERFACE LEVEL

       These interfaces are obsolete. Use ddi_dma_mem_alloc(9F) instead of ddi_iopb_alloc(). Use ddi_dma_mem_free(9F) instead of ddi_iopb_free().

PARAMETERS

   ddi_iopb_alloc()
       dip	       A pointer to the device's dev_info structure.

       limits	       A  pointer to a DMA limits structure for this device (see ddi_dma_lim_sparc(9S) or ddi_dma_lim_x86(9S)). If this pointer is
		       NULL, a default set of DMA limits is assumed.

       length	       The length in bytes of the desired allocation.

       iopbp	       A pointer to a caddr_t. On a successful return, *iopbp points to the allocated storage.

   ddi_iopb_free()
       iopb	       The iopb returned from a successful call to ddi_iopb_alloc().

DESCRIPTION

       ddi_iopb_alloc() allocates memory for  DMA transfers and should be used if the device accesses memory in a non-sequential  fashion,  or	if
       synchronization	steps  using  ddi_dma_sync(9F)	should	be as lightweight as possible, due to frequent use on small objects.  This type of
       access is commonly known as  consistent access. The allocation will obey the alignment and padding constraints as specified in  the  limits
       argument and other limits imposed by the system.

       Note  that you still must use DMA resource allocation functions (see ddi_dma_setup(9F)) to establish DMA resources for the memory allocated
       using ddi_iopb_alloc().

       In order to make the view of a memory object shared between a CPU and  a  DMA  device  consistent,  explicit  synchronization  steps  using
       ddi_dma_sync(9F)  or  ddi_dma_free(9F)  are  still required. The DMA resources will be allocated so that these synchronization steps are as
       efficient as possible.

       ddi_iopb_free() frees up memory allocated by ddi_iopb_alloc().

RETURN VALUES

       ddi_iopb_alloc() returns:

       DDI_SUCCESS     Memory successfully allocated.

       DDI_FAILURE     Allocation failed.

CONTEXT

       These functions can be called from user or interrupt context.

ATTRIBUTES

       See attributes(5) for a description of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Stability Level 	     |Obsolete			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       attributes(5),  ddi_dma_free(9F),  ddi_dma_mem_alloc(9F),  ddi_dma_mem_free(9F),  ddi_dma_setup(9F),  ddi_dma_sync(9F),	ddi_mem_alloc(9F),
       ddi_dma_lim_sparc(9S), ddi_dma_lim_x86(9S), ddi_dma_req(9S)

       Writing Device Drivers

NOTES

       This function uses scarce system resources. Use it selectively.

SunOS 5.10							    27 Sep 2002 						ddi_iopb_alloc(9F)
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