EXTENT(9)              NetBSD 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 identifica-
     tion in case of an error.  If the flag EX_NOCOALESCE is specified, only
     entire regions may be freed within the extent map, but internal coalesc-
     ing of regions is disabled so that extent_free() will never have to allo-
     cate 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().

     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 parame-
                      ters, 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 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 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 bound-
     ary 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 subre-
     gion 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 exten-
     sions 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 pro-
     vided.

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 suc-
     ceeds 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 sugges-
     tions.

NetBSD 6.1.5                  September 23, 1996                  NetBSD 6.1.5

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