192 lines
5.9 KiB
Groff
192 lines
5.9 KiB
Groff
.\"-
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.\" Copyright (c) 2001 Dag-Erling Coïdan Smørgrav
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd January 27, 2001
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.Dt ZONE 9
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.Os
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.Sh NAME
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.Nm zbootinit ,
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.Nm zinitna ,
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.Nm zinit ,
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.Nm zalloc ,
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.Nm zfree
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.Nd zone allocator
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.Sh SYNOPSIS
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.Fd #include <sys/types.h>
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.Fd #include <vm/vm_zone.h>
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.Ft void
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.Fn zbootinit "vm_zone_t z" "char *name" "int size" "void *item" "int nitems"
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.Ft int
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.Fn zinitna "vm_zone_t z" "struct vm_object *obj" "char *name" "int size" "int nentries" "int flags" "int zalloc"
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.Ft vm_zone_t
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.Fn zinit "char *name" "int size" "int nentries" "int flags" "int zalloc"
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.Ft void *
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.Fn zalloc "vm_zone_t z"
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.Ft void
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.Fn zfree "vm_zone_t z" "void *item"
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.Sh DESCRIPTION
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The zone allocator provides an efficient interface for managing
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dynamically-sized collections of items of similar size.
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The zone allocator can work with preallocated zones as well as with
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runtime-allocated ones, and is therefore available much earlier in the
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boot process than other memory management routines.
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.Pp
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A zone is an extensible collection of items of identical size.
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The zone allocator keeps track of which items are in use and which
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aren't, and provides functions for allocating items from the zone and
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for releasing them back (which makes them available for later use).
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.Pp
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The zone allocator stores state information inside the items proper,
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so structures that will be managed by the zone allocator must reserve
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two pointers at the very beginning for internal use by the zone
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allocator, as follows:
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.Bd -literal
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struct my_item {
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struct my_item *z_rsvd1;
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struct my_item *z_rsvd2;
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/* rest of structure */
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};
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.Ed
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.Pp
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Zones are created in one of two fashions, depending how far along the
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boot process is.
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.Pp
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If the VM system is fully initialized, a dynamically allocated zone can
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be created using
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.Fn zinit .
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The
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.Fa name
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argument should be a pointer to a short, descriptive name for the
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zone; it is used for statistics and debugging purposes.
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The
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.Fa size
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and
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.Fa nentries
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are the size of the items held by the zone and the initial size (in
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items) of the zone, respectively.
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The
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.Fa flags
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argument should be set to
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.Dv ZONE_INTERRUPT
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if there is a chance that items may be allocated from the zone in
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interrupt context; note that in this case, the zone will never grow
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larger than
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.Fa nentries
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items.
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In all other cases,
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.Fa flags
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should be set to 0.
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The final argument,
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.Fa zalloc ,
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indicates the number of VM pages by which the zone should grow every
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time it fills up.
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.Pp
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If the VM system is not yet fully initialized, the zone allocator
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cannot dynamically allocate VM pages from which to dole out items, so
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the caller needs to provide a static pool of items.
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In this case, the initialization is done in two stages: first,
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.Fn zbootinit
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is called before first use of the zone; later, when the VM system is
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up, the initialization of the zone is completed by calling
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.Fn zinitna .
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.Pp
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The first argument to
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.Fn zbootinit
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is a pointer to a static
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.Vt "struct vm_zone"
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to initialize.
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The second and third are the name of the zone and the size of the
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items it will hold.
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The fourth argument is a pointer to a static array of items from which
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the zone allocator will draw until the zone is fully initialized.
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The
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.Fa nitems
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argument is the number of items in the array.
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.Pp
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The arguments to
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.Fa zinitna
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are the same as for
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.Fa zinit ,
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with the addition of a pointer to the zone to initialize, and a
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pointer to a
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.Vt "struct vm_object"
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from which to allocate pages in the
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.Dv ZONE_INTERRUPT
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case.
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.Pp
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To allocate an item from a zone, simply call
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.Fn zalloc
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with a pointer to that zone; it will return a pointer to an item, or
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.Dv NULL
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in the rare case where all items in the zone are in use and the
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allocator is unable to grow the zone.
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.Pp
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Items are released back to the zone from which they were allocated by
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calling
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.Fn zfree
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with a pointer to the zone and a pointer to the item.
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.Sh RETURN VALUES
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The
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.Fn zinitna
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function returns 1 on success and 0 on failure; the only failure case
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is inability to preallocate address space for an interrupt-safe zone.
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.Pp
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The
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.Fn zinit
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function returns a pointer to a fully initialized
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.Vt "struct vm_zone" ,
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or
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.Dv NULL
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if it was unable to
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.Fn malloc
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a
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.Vt "struct vm_zone"
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or the
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.Dv ZONE_INTERRUPT
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flag was specified and
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.Fn zinitna
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failed to preallocate address space.
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.Pp
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The
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.Fn zalloc
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function returns a pointer to an item, or
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.Dv NULL
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if the zone ran out of unused items and the allocator was unable to
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enlarge it.
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.Sh SEE ALSO
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.Xr malloc 9
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.Sh HISTORY
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The zone allocator first appeared in
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.Fx 3.0 .
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.Sh AUTHORS
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.An -nosplit
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The zone allocator was written by
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.An John S. Dyson .
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.Pp
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This manual page was written by
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.An Dag-Erling Co\(:idan Sm\(/orgrav Aq des@FreeBSD.org .
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