xref: /freebsd/share/man/man9/vm_map_find.9 (revision fa9896e082a1046ff4fbc75fcba4d18d1f2efc19)

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.Dd September 12, 2013
.Dt VM_MAP_FIND 9
.Os
.Sh NAME
.Nm vm_map_find
.Nd find a free region within a map, and optionally map a vm_object
.Sh SYNOPSIS
.In sys/param.h
.In vm/vm.h
.In vm/vm_map.h
.Ft int
.Fo vm_map_find
.Fa "vm_map_t map" "vm_object_t object" "vm_ooffset_t offset"
.Fa "vm_offset_t *addr" "vm_size_t length" "vm_offset_t max_addr"
.Fa "int find_space" "vm_prot_t prot" "vm_prot_t max" "int cow"
.Fc
.Sh DESCRIPTION
The
.Fn vm_map_find
function attempts to find a free region in the target
.Fa map ,
with the given
.Fa length.
If a free region is found,
.Fn vm_map_find
creates a mapping of
.Fa object
via a call to
.Xr vm_map_insert 9 .
.Pp
The arguments
.Fa offset ,
.Fa prot ,
.Fa max ,
and
.Fa cow
are passed unchanged to
.Xr vm_map_insert 9
when creating the mapping, if and only if a free region is found.
.Pp
If
.Fa object
is
.Pf non- Dv NULL ,
the reference count on the object must be incremented
by the caller before calling this function to account for the new entry.
.Pp
If
.Fa max_addr
is non-zero,
it specifies an upper bound on the mapping.
The mapping will only succeed if a free region can be found that resides
entirely below
.Fa max_addr .
.Pp
The
.Fa find_space
argument specifies the strategy to use when searching for a free region of
the requested length.
For all values other than
.Dv VMFS_NO_SPACE ,
.Xr vm_map_findspace 9
is called to locate a free region of the requested length with a starting
address at or above
.Fa *addr .
The following strategies are supported:
.Bl -tag -width "Dv VMFS_ALIGNED_SPACE Ns"
.It Dv VMFS_NO_SPACE
The mapping will only succeed if there is a free region of the requested
length at the given address
.Fa *addr .
.It Dv VMFS_ANY_SPACE
The mapping will succeed as long as there is a free region.
.It Dv VMFS_SUPER_SPACE
The mapping will succeed as long as there is a free region that begins on
a superpage boundary.
If
.Fa object
is
.Pf non- Dv NULL
and is already backed by superpages,
then the mapping will require a free region that aligns relative to the
existing superpages rather than one beginning on a superpage boundary.
.It Dv VMFS_OPTIMAL_SPACE
The mapping will succeed as long as there is a free region.
However, if
.Fa object
is
.Pf non- Dv NULL
and is already backed by superpages,
this strategy will attempt to find a free region aligned relative to
the existing superpages.
.It Dv VMFS_ALIGNED_SPACE Ns Pq Fa n
The mapping will succeed as long as there is a free region that aligns on
a
.Pf 2^ Fa n
boundary.
.El
.Sh IMPLEMENTATION NOTES
This function acquires a lock on
.Fa map
by calling
.Xr vm_map_lock 9 ,
and holds it until the function returns.
.Pp
The search for a free region is defined to be first-fit, from the address
.Fa addr
onwards.
.Sh RETURN VALUES
The
.Fn vm_map_find
function returns
.Dv KERN_SUCCESS
if the mapping was successfully created.
If space could not be found or
.Fa find_space
was
.Dv VMFS_NO_SPACE
and the given address,
.Fa addr ,
was already mapped,
.Dv KERN_NO_SPACE
will be returned.
If the discovered range turned out to be bogus,
.Dv KERN_INVALID_ADDRESS
will be returned.
.Sh SEE ALSO
.Xr vm_map 9 ,
.Xr vm_map_findspace 9 ,
.Xr vm_map_insert 9 ,
.Xr vm_map_lock 9
.Sh AUTHORS
This manual page was written by
.An Bruce M Simpson Aq Mt bms@spc.org .