Manual Pages for UNIX Operating System command usage for man kmem_free

Kernel Functions for Drivers                       kmem_alloc(9F)



NAME
     kmem_alloc, kmem_zalloc, kmem_free - allocate kernel memory

SYNOPSIS
     #include 
     #include 



     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. Pos-
             sible  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
     The kmem_alloc() function 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 avail-
     able.  The  initial  contents  of  memory  allocated   using
     kmem_alloc() are random garbage.


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






SunOS 5.11          Last change: 16 Jan 2006                    1






Kernel Functions for Drivers                       kmem_alloc(9F)



     The kmem_free() function frees previously  allocated  kernel
     memory.  The  buffer address and size must exactly match the
     original allocation. Memory cannot 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 allocated  without  sleeping,  kmem_alloc()
     and kmem_zalloc() return NULL.

CONTEXT
     The kmem_alloc() and kmem_zalloc() functions can  be  called
     from  interrupt  context only if the KM_NOSLEEP flag is set.
     They can be called from user context with  any  valid  flag.
     The  kmem_free()  function  can  be  called  from from user,
     interrupt, or kernel 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  vir-
     tual address space, which is often the more restrictive con-
     straint 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, free-
     ing 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. Therefore, 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 5.11          Last change: 16 Jan 2006                    2