EXTENT(9) | Kernel Developer's Manual | EXTENT(9) |
extent
, extent_create
,
extent_destroy
, extent_alloc
,
extent_alloc_subregion
,
extent_alloc1
,
extent_alloc_subregion1
,
extent_alloc_region
,
extent_free
, extent_print
—
#include <sys/malloc.h>
#include <sys/extent.h>
struct extent *
extent_create
(char
*name, u_long
start, u_long end,
void *storage,
size_t storagesize,
int flags);
void
extent_destroy
(struct
extent *ex);
int
extent_alloc
(struct
extent *ex, u_long
size, u_long
alignment, u_long
boundary, int
flags, u_long
*result);
int
extent_alloc_subregion
(struct
extent *ex, u_long
substart, u_long
subend, u_long
size, u_long
alignment, u_long
boundary, u_long
flags, u_long
*result);
int
extent_alloc1
(struct
extent *ex, u_long
size, u_long
alignment, u_long
skew, u_long
boundary, int
flags, u_long
*result);
int
extent_alloc_subregion1
(struct extent
*ex, u_long substart, u_long
subend, u_long size, u_long
alignment, u_long skew, u_long
boundary, u_long flags, u_long
*result);
int
extent_alloc_region
(struct
extent *ex, u_long
start, u_long size,
int flags);
int
extent_free
(struct
extent *ex, u_long
start, u_long size,
int flags);
void
extent_print
(struct
extent *ex);
extent map
keeps track of allocated regions
within the number space.
extent_create
() creates an extent map
managing the space from start to
end inclusive. The extent map will have the name
name, used for identification in case of an error. If
the flag EX_NOCOALESCE
is specified, only entire
regions may be freed within the extent map, but internal coalescing of
regions is disabled so that extent_free
() will never
have to allocate a region descriptor and therefore will never fail. The
caller must specify one of the flags EX_NOWAIT
or
EX_WAITOK
, specifying whether it is okay to wait for
memory allocated for extent map overhead.
There are some applications which may want to use an extent map
but can't use malloc
() and
free
(). These applications may provide pre-allocated
storage for all descriptor overhead with the arguments
storage and storagesize. An
extent of this type is called a fixed extent
. If the
application can safely use malloc
() and
free
(), storage should be
NULL
. A fixed extent has a fixed number of region
descriptors, so care should be taken to provide enough storage for them;
alternatively, the flag EX_MALLOCOK
may be passed to
allocation requests to indicate that a fixed extent map may be extended
using a call to malloc
().
If the flag EX_EARLY
is specified, no
mutex(9) calls are made in the
expectation that mutual exclusion is not available or required.
extent_destroy
() destroys the extent map
ex, freeing all allocated regions. If the extent is
not a fixed extent, the region and internal extent descriptors themselves
are freed. This function always succeeds.
extent_alloc
() allocates a region in
extent ex of size size that fits
the provided parameters. There are two distinct allocation policies, which
are selected by the flags argument:
EX_FAST
The caller must specify if waiting for space in the extent is
allowed using the flag EX_WAITSPACE
. If
EX_WAITSPACE
is not specified, the allocation will
fail if the request can not be satisfied without sleeping. The caller must
also specify, using the EX_NOWAIT
or
EX_WAITOK
flags, if waiting for overhead allocation
is allowed. The request will be aligned to alignment
boundaries. Alignment values must be a power of 2. If no alignment is
necessary, the value 1 should be specified. If
boundary is nonzero, the allocated region will not
cross any of the numbers which are a multiple of
boundary. If the caller specifies the
EX_BOUNDZERO
flag, the boundary lines begin at zero.
Otherwise, the boundary lines begin at the beginning of the extent. The
allocated region may begin on a boundary address, but the end of the region
will not touch nor cross it. A boundary argument smaller than the size of
the request is invalid. Upon successful completion,
*result will contain the start of the allocated
region.
extent_alloc_subregion
() is similar to
extent_alloc
(), but it allows the caller to specify
that the allocated region must fall within the subregion from
substart to subend inclusive.
The other arguments and the return values of
extent_alloc_subregion
() are otherwise the same as
those of extent_alloc
().
extent_alloc_region
() allocates the
specific region in the extent map ex beginning at
start with the size size. The
caller must specify whether it is okay to wait for the indicated region to
be free using the flag EX_WAITSPACE
. If
EX_WAITSPACE
is not specified, the allocation will
fail if the request can not be satisfied without sleeping. The caller must
also specify, using the EX_NOWAIT
or
EX_WAITOK
flags, if waiting for overhead allocation
is allowed.
The extent_alloc1
() and
extent_alloc_subregion1
() functions are extensions
that take one additional argument, skew, that modifies
the requested alignment result in the following way: the value
(result -
skew) is aligned to alignment
boundaries. skew must be a smaller number than
alignment. Also, a boundary argument smaller than the
sum of the requested skew and the size of the request is invalid.
extent_free
() frees a region of
size bytes in extent ex starting
at start. If the extent has the
EX_NOCOALESCE
property, only entire regions may be
freed. If the extent has the EX_NOCOALESCE
property
and the caller attempts to free a partial region, behavior is undefined. The
caller must specify one of the flags EX_NOWAIT
or
EX_WAITOK
to specify whether waiting for memory is
okay; these flags have meaning in the event that allocation of a region
descriptor is required during the freeing process. This situation occurs
only when a partial region that begins and ends in the middle of another
region is freed. Behavior is undefined if invalid arguments are
provided.
extent_print
() Print out information about
extent ex. This function always succeeds. Behavior is
undefined if invalid arguments are provided.
EX_EARLY
is specified) on the extent map itself, and
any other data structures internal to the extent manager. The locks used by
the extent manager are simplelocks, and will never sleep (see
lock(9)). This should be taken
into account when designing the locking protocol for users of the extent
manager.
extent_create
() returns the extent map on
success, or NULL
if it fails to allocate storage for
the extent map. It always succeeds when creating a fixed extent or when given
the flag EX_WAITOK
.
extent_alloc
(),
extent_alloc_region
(),
extent_alloc_subregion
(), and
extent_free
() return one of the following values:
0
ENOMEM
EX_NOWAIT
is specified, the extent manager was
not able to allocate a region descriptor for the new region or to split a
region when freeing a partial region.EAGAIN
EX_WAITSPACE
was not specified.EINTR
extent_free
().void func() { struct extent *foo_ex; u_long region_start; int error; /* * Extent "foo" manages a 256k region starting at 0x0 and * only allows complete regions to be freed so that * extent_free() never needs to allocate memory. */ foo_ex = extent_create("foo", 0x0, 0x3ffff, M_DEVBUF, NULL, 0, EX_WAITOK | EX_NOCOALESCE); /* * Allocate an 8k region, aligned to a 4k boundary, which * does not cross any of the 3 64k boundaries (at 64k, * 128k, and 192k) within the extent. */ error = extent_alloc(foo_ex, 0x2000, 0x1000, 0x10000, EX_NOWAIT, ®ion_start); if (error) panic("you lose"); /* * Give up the extent. */ extent_destroy(foo_ex); }
The i386 bus management code uses the extent manager for managing I/O ports and I/O memory. This code is in the file sys/arch/i386/i386/machdep.c.
August 28, 2017 | NetBSD 9.0 |