Kernel Functions for Drivers                       kmemalloc(9F)



NAME
     kmemalloc, kmemzalloc, kmemfree - allocate kernel memory

SYNOPSIS
     #include 
     #include 



     void *kmemalloc(sizet size, int flag);


     void *kmemzalloc(sizet size, int flag);


     void kmemfree(void*buf, sizet size);


INTERFACE LEVEL
     Architecture independent level 1 (DI/DKI).

PARAMETERS
     size    Number of bytes to allocate.


     flag    Determines whether caller can sleep for memory. Pos-
             sible  flags  are   KMSLEP to allow sleeping until
             memory is available, or KMNOSLEP  to  return  NUL
             immediately if memory is not available.


     buf     Pointer to allocated memory.


DESCRIPTION
     The kmemalloc() 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. KMSLEP allocations may sleep but are guaranteed to
     succeed. KMNOSLEP allocations are guaranteed not to  sleep
     but  may fail (return NUL) if no memory is currently avail-
     able.  The  initial  contents  of  memory  allocated   using
     kmemalloc() are random garbage.


     The kmemzalloc() function is like kmemalloc() but  returns
     zero-filled memory.






SunOS 5.11          Last change: 16 Jan 2006                    1






Kernel Functions for Drivers                       kmemalloc(9F)



     The kmemfree() 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,  kmemalloc()  and  kmemzalloc()  return  a
     pointer  to  the  allocated memory. If KMNOSLEP is set and
     memory cannot be allocated  without  sleeping,  kmemalloc()
     and kmemzalloc() return NUL.

CONTEXT
     The kmemalloc() and kmemzalloc() functions can  be  called
     from  interrupt  context only if the KMNOSLEP flag is set.
     They can be called from user context with  any  valid  flag.
     The  kmemfree()  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 kmemalloc() 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  kmemalloc()
     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
     kmemalloc(0, flag) always returns NUL. kmemfree(NUL,  0)
     is legal.



SunOS 5.11          Last change: 16 Jan 2006                    2