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)