xref: /illumos-gate/usr/src/man/man9f/vmem_alloc.9f (revision 72d3dbb9)

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.\" Copyright 2017, Richard Lowe.
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.Dd Jan 18, 2017
.Dt VMEM_ALLOC 9F
.Os
.Sh NAME
.Nm vmem_alloc ,
.Nm vmem_xalloc ,
.Nm vmem_free ,
.Nm vmem_xfree
.Nd allocate and free segments from a vmem arena
.Sh SYNOPSIS
.In sys/vmem.h
.Ft void *
.Fo vmem_alloc
.Fa "vmem_t *vmp"
.Fa "size_t size"
.Fa "int vmflag"
.Fc
.Ft void *
.Fo vmem_xalloc
.Fa "vmem_t *vmp"
.Fa "size_t size"
.Fa "size_t align_arg"
.Fa "size_t phase"
.Fa "size_t nocross"
.Fa "void *minaddr"
.Fa "void *maxaddr"
.Fa "int vmflag"
.Fc
.Ft void
.Fo vmem_free
.Fa "vmem_t *vmp"
.Fa "void *vaddr"
.Fa "size_t size"
.Fc
.Ft void
.Fo vmem_xfree
.Fa "vmem_t *vmp"
.Fa "void *vaddr"
.Fa "size_t size"
.Fc
.Sh INTERFACE LEVEL
illumos DDI specific
.Sh PARAMETERS
.Bl -tag -width Ds
.It Fa vmp
The vmem arena from which to allocate or free.
.It Fa size
The size of the segment to allocate or free.
.It Fa vmflag
A bitmask of flags controlling the behaviour of the allocation.
There are two meaningful groups of flags.
.Dv VM_SLEEP
or
.Dv VM_NOSLEEP
must be specified, and indicate whether the allocation may block.
A
.Dv VM_SLEEP
allocation can never fail but may block indefinitely.
.Pp
The allocation policy may be specified by one of the following flags:
.Bl -tag -width Ds
.It Dv VM_BESTFIT
Take the segment from the smallest free segment that could satisfy this
allocation.
.It Dv VM_FIRSTFIT
Take the segment from the first free segment found that could satisfy this
allocation.
.It Dv VM_NEXTFIT
Take the segment from the segment after the one previously allocated.
This
provides sequential behaviour useful when allocating identifiers from a
.Dv VMC_IDENTIFIER
arena.
.It Dv VM_ENDALLOC
May be specified in combination with
.Dv VM_BESTFIT ,
.Dv VM_FIRSTFIT
or the default policy to indicate that the higher addresses should be
preferred.
.El
.Pp
The default (unnamed) allocation policy is
.Dq "instant fit" ,
an approximation of
.Dv VM_BESTFIT
in guaranteed constant time.
.It Fa align_arg
The minimum alignment of the allocation.
If 0, the allocated segment will be aligned as the arena's quantum.
.It Fa phase
The allocated segment must be
.Fa phase
bytes from the alignment boundary.
.It Fa nocross
The allocated segment may not straddle a
.Fa nocross
alignment boundary.
.It Fa minaddr
The minimum address at which the segment may be allocated.
.It Fa maxaddr
The maximum address which may be included in the segment.
.It Fa vaddr
The address of the segment which
.Fn vmem_free
or
.Fn vmem_xfree
should free.
.El
.Sh DESCRIPTION
The
.Fn vmem_alloc
and
.Fn vmem_xalloc
functions allocate a segment of
.Fa size
length from the vmem arena
.Fa vmp .
.Pp
The
.Fa vmflag
argument controls the behaviour of the allocation, as described in
.Sx PARAMETERS .
.Pp
For allocations with complex requirements, such as those used for DMA
.Fn vmem_xalloc
takes additional arguments allowing those requirements to be expressed.
.Pp
Segments allocated with
.Fn vmem_xalloc
must always be freed with
.Fn vmem_xfree ,
since these allocations are uncached.
.Sh CONTEXT
This function can be called from either user or kernel context.
If the
.Dv VM_NOSLEEP
flag is specified, it may also be called from interrupt context.
.Sh RETURN VALUES
Upon successful completion the
.Fn vmem_alloc
and
.Fn vmem_xalloc
functions return a pointer to the beginning of the allocated segment.
In the case of a
.Dv VMC_IDENTIFIER
arena, the address of this pointer is the meaningful component, not the value
to which it points.
.Pp
On failure,
.Dv NULL
is returned.
When the
.Dv VM_SLEEP
flag is specified, these functions can never fail (but may block forever).
.Sh SEE ALSO
.Xr vmem 9 ,
.Xr vmem_contains 9F ,
.Xr vmem_create 9F