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VMEM_ALLOC(9F) |
Kernel Functions for Drivers |
VMEM_ALLOC(9F) |
NAME
vmem_alloc, vmem_xalloc, vmem_free, vmem_xfree — allocate and free segments from a vmem arena
SYNOPSIS
#include <sys/vmem.h>
void *
vmem_alloc(
vmem_t *vmp,
size_t size,
int vmflag);
void *
vmem_xalloc(
vmem_t *vmp,
size_t size,
size_t align_arg,
size_t phase,
size_t nocross,
void *minaddr,
void *maxaddr,
int vmflag);
void
vmem_free(
vmem_t *vmp,
void *vaddr,
size_t size);
void
vmem_xfree(
vmem_t *vmp,
void *vaddr,
size_t size);
INTERFACE LEVEL
illumos DDI specific
PARAMETERS
-
vmp
-
The vmem arena from which to allocate or free.
-
size
-
The size of the segment to allocate or free.
-
vmflag
-
A bitmask of flags controlling the behaviour of the allocation. There are two meaningful groups of flags. VM_SLEEP or VM_NOSLEEP must be specified, and indicate whether the allocation may block. A VM_SLEEP allocation can never fail but may block indefinitely.
The allocation policy may be specified by one of the following flags:
-
VM_BESTFIT
-
Take the segment from the smallest free segment that could satisfy this allocation
-
VM_FIRSTFIT
-
Take the segment from the first free segment found that could satisfy this allocation.
-
VM_NEXTFIT
-
Take the segment from the segment after the one previously allocated. This provides sequential behaviour useful when allocating identifiers from a VMC_IDENTIFIER arena.
-
VM_ENDALLOC
-
May be specified in combination with VM_BESTFIT, VM_FIRSTFIT or the default policy to indicate that the higher addresses should be preferred.
The default (un-named) allocation policy is “instant fit” an approximation of VM_BESTFIT in guaranteed constant time.
-
align_arg
-
The minimum alignment of the allocation. If ‘
0’ the allocated segment will be aligned as the arena's quantum.
-
phase
-
The allocated segment must be phase bytes from the alignment boundary.
-
nocross
-
The allocated segment may not straddle a nocross alignment boundary.
-
minaddr
-
The minimum address at which the segment may be allocated.
-
maxaddr
-
The maximum address which may be included in the segment.
-
vaddr
-
The address of the segment which vmem_free() or vmem_xfree() should free.
DESCRIPTION
The
vmem_alloc() and
vmem_xalloc() functions allocate a segment of
size length from the vmem arena
vmp.
The
vmflag argument controls the behaviour of the allocation. As described in
PARAMETERS
For allocations with complex requirements, such as those used for DMA
vmem_xalloc() takes additional arguments allowing those requirements to be expressed.
Segments allocated with
vmem_xalloc() must always be freed with
vmem_xfree(), since these allocations are uncached.
CONTEXT
This function can be called from either user or kernel context. If the VM_NOSLEEP flag is specified, it may also be called from interrupt context.
RETURN VALUES
Upon successful completion the
vmem_alloc() and
vmem_xalloc() functions return a pointer to the beginning of the allocated segment. In the case of a
VMC_IDENTIFIER arena, the address of this pointer is the meaningful component, not the value to which it points.
On failure,
NULL is returned. When the
VM_SLEEP flag is specified, these functions can never fail (but may block forever).