NAME
extent
,
extent_create
,
extent_destroy
,
extent_alloc
,
extent_alloc_subregion
,
extent_alloc1
,
extent_alloc_subregion1
,
extent_alloc_region
,
extent_free
, extent_print
— general purpose extent
manager
SYNOPSIS
#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);
DESCRIPTION
The NetBSD extent manager provides
management of areas of memory or other number spaces (such as I/O ports). An
opaque structure called an 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
- Allocate the first region that fits the provided parameters, regardless of resulting extent fragmentation.
- default
- Allocate the smallest region that is capable of holding the request, thus minimizing fragmentation of the extent.
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.
LOCKING
The extent manager performs all necessary locking (unless
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.
RETURN VALUES
The behavior of all extent manager functions is undefined if given
invalid arguments. 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
- Operation was successful.
ENOMEM
- If
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
- Requested region is not available and
EX_WAITSPACE
was not specified. EINTR
- Process received a signal while waiting for the requested region to become
available in the extent. Does not apply to
extent_free
().
EXAMPLES
Here is an example of a (useless) function that uses several of the extent manager routines.
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); }
CODE REFERENCES
The extent manager itself is implemented within the file sys/kern/subr_extent.c. Function prototypes for the framework are located in sys/sys/extent.h.
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.
SEE ALSO
HISTORY
The NetBSD extent manager appeared in NetBSD 1.3.
AUTHORS
The NetBSD extent manager was architected
and implemented by Jason R. Thorpe
⟨thorpej@NetBSD.org⟩.
Matthias Drochner
⟨drochner@zelux6.zel.kfa-juelich.de⟩ contributed to the
initial testing and optimization of the implementation.
Chris Demetriou ⟨cgd@NetBSD.org⟩
contributed many architectural suggestions.