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

NAME

       kmem_alloc, kmem_zalloc, kmem_free - allocate kernel memory

SYNOPSIS

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

       void *kmem_alloc(size_t size, int flag);

       void *kmem_zalloc(size_t size, int flag);

       void kmem_free(void*buf, size_t size);

INTERFACE LEVEL

       Architecture independent level 1 (DDI/DKI).

PARAMETERS

       size            Number of bytes to allocate.

       flag            Determines  whether caller can sleep for memory.  Possible flags are  KM_SLEEP to allow sleeping until memory is available,
                       or KM_NOSLEEP to return  NULL immediately if memory is not available.

       buf             Pointer to allocated memory.

DESCRIPTION

       kmem_alloc() allocates size bytes of kernel memory and returns a pointer to the allocated memory. The allocated memory is at least  double-
       word  aligned,  so  it can hold any C data structure. No greater alignment can be assumed. flag determines whether the caller can sleep for
       memory. KM_SLEEP allocations may sleep but are guaranteed to succeed. KM_NOSLEEP allocations are guaranteed  not  to  sleep  but  may  fail
       (return NULL) if no memory is currently available. The initial contents of memory allocated using kmem_alloc() are random garbage.

       kmem_zalloc() is like  kmem_alloc() but returns zero-filled memory.

       kmem_free()  frees previously allocated kernel memory.  The buffer address and size must exactly match the original allocation. Memory can-
       not be returned piecemeal.

RETURN VALUES

       If successful, kmem_alloc() and kmem_zalloc() return a pointer to the allocated memory. If  KM_NOSLEEP is set and memory  cannot  be  allo-
       cated without sleeping, kmem_alloc() and kmem_zalloc() return NULL.

CONTEXT

       kmem_alloc()  and  kmem_zalloc() can be called from interrupt context only if the KM_NOSLEEP flag is set. They can be called from user con-
       text with any valid flag. kmem_free() can be called from user or interrupt context.

SEE ALSO

       copyout(9F), freerbuf(9F), getrbuf(9F)

       Writing Device Drivers

WARNINGS

       Memory allocated using  kmem_alloc() is not 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 restrictive constraint on large-memory configurations.

       Excessive  use  of  kernel memory is likely to affect overall system performance.  Overcommitment of kernel memory will cause the system to
       hang or panic.

       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 a null or invalid pointer, will corrupt the kernel heap and may cause the system to corrupt data or panic.

       The  initial contents of memory allocated using kmem_alloc() are random garbage. This random garbage may include secure kernel data. There-
       fore, uninitialized kernel memory should be handled carefully.  For example, never copyout(9F) a potentially uninitialized buffer.

NOTES

       kmem_alloc(0, flag) always returns NULL. kmem_free(NULL, 0) is legal.

SunOS 5.10                                                          24 Mar 2003                                                     kmem_alloc(9F)