.\" $NetBSD: extent.9,v 1.10 1998/06/06 02:32:28 thorpej Exp $ .\" .\" Copyright (c) 1996, 1998 The NetBSD Foundation, Inc. .\" All rights reserved. .\" .\" This code is derived from software contributed to The NetBSD Foundation .\" by Jason R. Thorpe and Greg Hudson. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. All advertising materials mentioning features or use of this software .\" must display the following acknowledgement: .\" This product includes software developed by the NetBSD .\" Foundation, Inc. and its contributors. .\" 4. Neither the name of The NetBSD Foundation nor the names of its .\" contributors may be used to endorse or promote products derived .\" from this software without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS .\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED .\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR .\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS .\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR .\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF .\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS .\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN .\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE .\" POSSIBILITY OF SUCH DAMAGE. .\" .Dd September 23, 1996 .Dt EXTENT 9 .Os NetBSD .Sh NAME .Nm extent , .Nm extent_create , .Nm extent_destroy , .Nm extent_alloc , .Nm extent_alloc_subregion , .Nm extent_alloc_region , .Nm extent_free , .Nm extent_print .Nd general purpose extent manager .Sh SYNOPSIS .Fd #include .Fd #include .Ft struct extent * .Fn extent_create "char *name" "u_long start" "u_long end" "int mtype" "caddr_t storage" "size_t storagesize" "int flags" .Ft void .Fn extent_destroy "struct extent *ex" .Ft int .Fn extent_alloc "struct extent *ex" "u_long size" "u_long alignment" "u_long boundary" "int flags" "u_long *result" .Ft int .Fn 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" .Ft int .Fn extent_alloc_region "struct extent *ex" "u_long start" "u_long size" "int flags" .Ft int .Fn extent_free "struct extent *ex" "u_long start" "u_long size" "int flags" .Ft void .Fn extent_print "struct extent *ex" .Sh DESCRIPTION The .Nx extent manager provides management of areas of memory or other number spaces (such as I/O ports). An opaque structure called an .Nm extent map keeps track of allocated regions within the number space. .Pp .Fn extent_create creates an extent map managing the space from .Fa start to .Fa end inclusive. All memory allocation will use the memory type .Fa mtype (see .Xr malloc 9 ). The extent map will have the name .Fa name , used for identification in case of an error. If the flag .Dv EX_NOCOALESCE is specified, only entire regions may be freed within the extent map, but internal coalescing of regions is disabled so that .Fn extent_free will never have to allocate a region descriptor and therefore will never fail. The caller must specify one of the flags .Dv EX_NOWAIT or .Dv EX_WAITOK , specifying whether it is okay to wait for memory allocated for extent map overhead. .Pp There are some applications which may want to use an extent map but can't use .Fn malloc and .Fn free . These applications may provide pre-allocated storage for all descriptor overhead with the arguments .Fa storage and .Fa storagesize . An extent of this type is called a .Nm fixed extent . If the application can safely use .Fn malloc and .Fn free , .Fa storage should be .Dv 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 .Dv EX_MALLOCOK may be passed to allocation requests to indicate that a fixed extent map may be extended using a call to .Fn malloc . .Pp .Fn extent_destroy destroys the extent map .Fa 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. .Pp .Fn extent_alloc allocates a region in extent .Fa ex of size .Fa size that fits the provided parameters. There are two distinct allocation policies, which are selected by the .Fa flags argument: .Bl -tag -offset indent -width "XXXXXXXXX" .It Dv EX_FAST Allocate the first region that fits the provided paramters, regardless of resulting extent fragmentation. .It default Allocate the smallest region that is capable of holding the request, thus minimizing fragmentation of the extent. .El .Pp The caller must specify if waiting for space in the extent is allowed using the flag .Dv EX_WAITSPACE . If .Dv 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 .Dv EX_NOWAIT or .Dv EX_WAITOK flags, if waiting for overhead allocation is allowed. The request will be aligned to .Fa alignment boundaries. Alignment values must be a power of 2. If no alignment is necessary, the value 1 should be specified. If .Fa boundary is nonzero, the allocated region will not cross any of the numbers which are a multiple of .Fa boundary . If the caller specifies the .Dv 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, .Fa *result will contain the start of the allocated region. .Pp .Fn extent_alloc_subregion is similar to .Fn extent_alloc , but it allows the caller to specify that the allocated region must fall within the subregion from .Fa substart to .Fa subend inclusive. The other arguments and the return values of .Fn extent_alloc_subregion are otherwise the same as those of .Fn extent_alloc . .Pp .Fn extent_alloc_region allocates the specific region in the extent map .Fa ex beginning at .Fa start with the size .Fa size . The caller must specify whether it is okay to wait for the indicated region to be free using the flag .Dv EX_WAITSPACE . If .Dv 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 .Dv EX_NOWAIT or .Dv EX_WAITOK flags, if waiting for overhead allocation is allowed. .Pp .Fn extent_free frees a region of .Fa size bytes in extent .Fa ex starting at .Fa start . If the extent has the .Dv EX_NOCOALESCE property, only entire regions may be freed. If the extent has the .Dv EX_NOCOALESCE property and the caller attempts to free a partial region, behavior is undefined. The caller must specify one of the flags .Dv EX_NOWAIT or .Dv 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. .Pp .Fn extent_print Print out information about extent .Fa ex . This function always succeeds. Behavior is undefined if invalid arguments are provided. .Sh 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 spin locks, and will never sleep. This should be taken into account when designing the locking protocol for users of the extent manager. .Sh RETURN VALUES The behavior of all extent manager functions is undefined if given invalid arguments. .Fn extent_create returns the extent map on success, or .Dv NULL if it fails to allocate storage for the extent map. It always succeeds when creating a fixed extent or when given the flag .Dv EX_WAITOK . .Fn extent_alloc , .Fn extent_alloc_region , .Fn extent_alloc_subregion , and .Fn extent_free return one of the following values: .Bl -tag -offset indent -width "XXXXXXXX" .It Dv 0 Operation was successful. .It Dv ENOMEM If .Dv 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. .It Dv EAGAIN Requested region is not available and .Dv EX_WAITSPACE was not specified. .It Dv EINTR Process received a signal while waiting for the requested region to become available in the extent. Does not apply to .Fn extent_free . .El .Sh EXAMPLES Here is an example of a (useless) function that uses several of the extent manager routines. .Bd -literal 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); } .Ed .Sh CODE REFERENCES This section describes places within the .Nx source tree where actual code implementing or using the extent manager can be found. All pathnames are relative to .Nm /usr/src . .Pp The extent manager itself is implemented within the file .Nm sys/kern/subr_extent.c . Function prototypes for the framework are located in .Nm sys/sys/extent.h . .Pp The i386 bus management code uses the extent manager for managing I/O ports and I/O memory. This code is in the file .Nm sys/arch/i386/i386/machdep.c . .Sh AUTHOR The .Nx extent manager was architected and implemented by Jason R. Thorpe . Matthias Drochner contributed to the initial testing and optimization of the implementation. Chris Demetriou contributed many architectural suggestions. .Sh SEE ALSO .Xr malloc 9 . .Sh HISTORY The .Nx extent manager appeared in .Nx 1.3 .