kmem_alloc(D3)kmem_alloc(D3)NAMEkmem_alloc - allocate space from kernel free memory
SYNOPSIS
#include <sys/types.h>
#include <sys/kmem.h>
#include <sys/ddi.h>
void *kmem_alloc(size_t size, int flag);
Arguments
size Number of bytes to allocate.
flag Specifies whether the caller is willing to sleep waiting for
memory, etc.
DESCRIPTIONkmem_alloc allocates size bytes of kernel memory and returns a pointer to
the allocated memory. If flag is set to KM_SLEEP, the caller will sleep
if necessary until the specified amount of memory is available. If flag
is set to KM_NOSLEEP, the caller will not sleep, but kmem_alloc will
return NULL if the specified amount of memory is not immediately
available. KM_PHYSCONTIG: Allocate contiguous physical memory.
CAUTION: It is best to call kmem_alloc with this flag only at driver
initialization time. Otherwise, it may sleep for a very long time.
KM_CACHEALIGN: Allocate the requested memory starting at a cache line
boundary. This also pads the buffer out to a full cache line. Buffers
that the driver will use for DMA must be cache-line aligned and padded to
a full cache line.
Return Values
Upon successful completion, kmem_alloc returns a pointer to the allocated
memory. If KM_NOSLEEP is specified and sufficient memory is not
immediately available, kmem_alloc returns a NULL pointer. If size is set
to 0, kmem_alloc returns NULL regardless of the value of flag.
USAGE
Kernel memory is a limited resource and should be used judiciously.
Memory allocated using kmem_alloc should be freed as soon as possible.
Drivers should not use local freelists for memory or similar schemes that
cause the memory to be held for longer than necessary.
Since holding memory allocated using kmem_alloc for extended periods of
time (e.g allocating memory at system startup and never freeing it) can
have an adverse effect on overall memory usage and system performance,
memory needed for such extended periods should be statically allocated
whenever possible.
Page 1
kmem_alloc(D3)kmem_alloc(D3)
The address returned by a successful call to kmem_alloc is word-aligned.
Level
Base only if flag is set to KM_SLEEP.
Initialization, Base or Interrupt if flag is set to KM_NOSLEEP.
Synchronization Constraints
May sleep if flag is set to KM_SLEEP.
Driver-defined basic locks and read/write locks may be held across calls
to this function if flag is KM_NOSLEEP, but may not be held if flag is
KM_SLEEP.
Driver-defined sleep locks may be held across calls to this function
regardless of the value of flag.
Note
kmem_alloc and kmem_free are intended as replacements for kern_malloc and
kern_free. Drivers should use these routines rather than kern_malloc and
kern_free.
REFERENCESkmem_free(D3), kmem_zalloc(D3), Appendix A, Section A.2, "Data cache
Write Back and Invalidation" of the IRIX Device Driver Programming Guide
Page 2
