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NetBSD 6.1.5 - man page for extent_free (netbsd section 9)

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EXTENT(9)			  BSD Kernel Developer's Manual 			EXTENT(9)

NAME
     extent, extent_create, extent_destroy, extent_alloc, extent_alloc_subregion,
     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, int mtype, 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.  All
     memory allocation will use the memory type mtype (see malloc(9)).	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 over-
     head.

     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().

     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 parame-
     ters.  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 neces-
     sary, 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 allo-
     cation 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 unde-
     fined.  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 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, &region_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
     malloc(9)

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.

BSD					September 23, 1996				      BSD
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