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

NAME

       ddi_umem_alloc, ddi_umem_free - allocate and free page-aligned kernel memory

SYNOPSIS

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

       void *ddi_umem_alloc(size_t size, int flag, ddi_umem_cookie_t *cookiep);

       void ddi_umem_free(ddi_umem_cookie_t cookie);

INTERFACE LEVEL

       Solaris DDI specific (Solaris DDI).

PARAMETERS

   ddi_umem_alloc()
       size	Number of bytes to allocate.

       flag	Used to determine the sleep and pageable conditions.

		Possible sleep flags are DDI_UMEM_SLEEP, which allows sleeping until memory is available, and DDI_UMEM_NOSLEEP, which returns NULL
		immediately if memory is not available.

		The default condition is to allocate locked memory; this can be changed to allocate pageable memory  using  the  DDI_UMEM_PAGEABLE
		flag.

       cookiep	Pointer to a kernel memory cookie.

   ddi_umem_free()
       cookie	A kernel memory cookie allocated in ddi_umem_alloc().

DESCRIPTION

       ddi_umem_alloc()  allocates  page-aligned  kernel  memory and returns a pointer to the allocated memory. The number of bytes allocated is a
       multiple of the system page size (roundup of size). The allocated memory can be used in the kernel and can be exported to user  space.  See
       devmap(9E) and devmap_umem_setup(9F) for further information.

       flag  determines  whether the caller can sleep for memory and whether the allocated memory is locked or not. DDI_UMEM_SLEEP allocations may
       sleep but are guaranteed to succeed. DDI_UMEM_NOSLEEP allocations do not sleep but may fail (return NULL) if memory is  currently  unavail-
       able.  If DDI_UMEM_PAGEABLE is set, pageable memory will be allocated. These pages can be swapped out to secondary memory devices. The ini-
       tial contents of memory allocated using ddi_umem_alloc() is zero-filled.

       *cookiep is a pointer to the kernel memory cookie that describes the kernel memory  being  allocated.  A  typical  use  of  cookiep  is	in
       devmap_umem_setup(9F) when the drivers want to export the kernel memory to a user application.

       To  free  the allocated memory, a driver calls ddi_umem_free() with the cookie obtained from ddi_umem_alloc(). ddi_umem_free() releases the
       entire buffer.

RETURN VALUES

       Non-null        Successful completion.ddi_umem_alloc() returns a pointer to the allocated memory.

       NULL	       Memory cannot be allocated by ddi_umem_alloc() because DDI_UMEM_NOSLEEP is set and the system is out of resources.

CONTEXT

       ddi_umem_alloc() can be called from any context if flag is set to DDI_UMEM_NOSLEEP. If  DDI_UMEM_SLEEP  is  set,  ddi_umem_alloc()  can	be
       called from user and kernel context only. ddi_umem_free() can be called from any context.

SEE ALSO

       devmap(9E), condvar(9F), devmap_umem_setup(9F), kmem_alloc(9F), mutex(9F), rwlock(9F), semaphore(9F)

       Writing Device Drivers

WARNINGS

       Setting	the DDI_UMEM_PAGEABLE flag in ddi_umem_alloc() will result in an allocation of pageable memory. Because these pages can be swapped
       out to secondary memory devices, drivers should use this flag with care. This memory must not be used for the following purposes:

	 o  For synchronization objects such as locks and condition variables. See mutex(9F), semaphore(9F), rwlock(9F), and condvar(9F).

	 o  For driver interrupt routines.

       Memory allocated using ddi_umem_alloc() without setting DDI_UMEM_PAGEABLE flag cannot be paged. Available memory is  therefore  limited	by
       the total physical memory on the system. It is also limited by the available kernel virtual address space, which is often the more restric-
       tive constraint on large-memory configurations.

       Excessive use of kernel memory is likely to effect overall system performance. Over-commitment of kernel  memory  may  cause  unpredictable
       consequences.

       Misuse  of  the kernel memory allocator, such as writing past the end of a buffer, using a buffer after freeing it, freeing a buffer twice,
       or freeing an invalid pointer, will cause the system to corrupt data or panic.

       Do not call ddi_umem_alloc() within DDI_SUSPEND and DDI_RESUME operations. Memory acquired at these times is not reliable. In  some  cases,
       such a call can cause a system to hang.

NOTES

       ddi_umem_alloc(0, flag, cookiep) always returns NULL. ddi_umem_free(NULL) has no effects on system.

SunOS 5.10							    19 Mar 2002 						ddi_umem_alloc(9F)