519 lines
13 KiB
Groff
519 lines
13 KiB
Groff
.\"
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.\" Copyright (c) 2009 Advanced Computing Technologies LLC
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.\" Written by: John H. Baldwin <jhb@FreeBSD.org>
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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 12, 2014
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.Dt SGLIST 9
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.Os
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.Sh NAME
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.Nm sglist ,
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.Nm sglist_alloc ,
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.Nm sglist_append ,
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.Nm sglist_append_bio ,
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.Nm sglist_append_mbuf ,
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.Nm sglist_append_phys ,
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.Nm sglist_append_uio ,
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.Nm sglist_append_user ,
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.Nm sglist_build ,
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.Nm sglist_clone ,
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.Nm sglist_consume_uio ,
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.Nm sglist_count ,
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.Nm sglist_free ,
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.Nm sglist_hold ,
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.Nm sglist_init ,
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.Nm sglist_join ,
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.Nm sglist_length ,
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.Nm sglist_reset ,
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.Nm sglist_slice ,
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.Nm sglist_split
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.Nd manage a scatter/gather list of physical memory addresses
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.Sh SYNOPSIS
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.In sys/types.h
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.In sys/sglist.h
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.Ft struct sglist *
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.Fn sglist_alloc "int nsegs" "int mflags"
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.Ft int
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.Fn sglist_append "struct sglist *sg" "void *buf" "size_t len"
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.Ft int
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.Fn sglist_append_bio "struct sglist *sg" "struct bio *bp"
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.Ft int
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.Fn sglist_append_mbuf "struct sglist *sg" "struct mbuf *m"
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.Ft int
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.Fn sglist_append_phys "struct sglist *sg" "vm_paddr_t paddr" "size_t len"
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.Ft int
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.Fn sglist_append_uio "struct sglist *sg" "struct uio *uio"
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.Ft int
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.Fn sglist_append_user "struct sglist *sg" "void *buf" "size_t len" "struct thread *td"
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.Ft struct sglist *
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.Fn sglist_build "void *buf" "size_t len" "int mflags"
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.Ft struct sglist *
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.Fn sglist_clone "struct sglist *sg" "int mflags"
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.Ft int
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.Fn sglist_consume_uio "struct sglist *sg" "struct uio *uio" "size_t resid"
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.Ft int
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.Fn sglist_count "void *buf" "size_t len"
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.Ft void
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.Fn sglist_free "struct sglist *sg"
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.Ft struct sglist *
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.Fn sglist_hold "struct sglist *sg"
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.Ft void
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.Fn sglist_init "struct sglist *sg" "int maxsegs" "struct sglist_seg *segs"
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.Ft int
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.Fn sglist_join "struct sglist *first" "struct sglist *second"
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.Ft size_t
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.Fn sglist_length "struct sglist *sg"
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.Ft void
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.Fn sglist_reset "struct sglist *sg"
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.Ft int
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.Fn sglist_slice "struct sglist *original" "struct sglist **slice" "size_t offset" "size_t length" "int mflags"
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.Ft int
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.Fn sglist_split "struct sglist *original" "struct sglist **head" "size_t length" "int mflags"
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.Sh DESCRIPTION
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The
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.Nm
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API manages physical address ranges.
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Each list contains one or more elements.
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Each element contains a starting physical address and a length.
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Scatter/gather lists are read-only while they are shared.
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If one wishes to alter an existing scatter/gather list and does not hold the
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sole reference to the list,
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then one should create a new list instead of modifying the existing list.
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.Pp
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Each scatter/gather list object contains a reference count.
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New lists are created with a single reference.
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New references are obtained by calling
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.Nm sglist_hold
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and are released by calling
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.Nm sglist_free .
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.Ss Allocating and Initializing Lists
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Each
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.Nm
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object consists of a header structure and a variable-length array of
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scatter/gather list elements.
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The
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.Nm sglist_alloc
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function allocates a new list that contains a header and
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.Fa nsegs
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scatter/gather list elements.
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The
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.Fa mflags
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argument can be set to either
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.Dv M_NOWAIT
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or
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.Dv M_WAITOK .
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.Pp
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The
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.Nm sglist_count
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function returns the number of scatter/gather list elements needed to describe
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the physical address ranges mapped by a single kernel virtual address range.
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The kernel virtual address range starts at
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.Fa buf
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and is
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.Fa len
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bytes long.
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.Pp
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The
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.Nm sglist_build
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function allocates a new scatter/gather list object that describes the physical
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address ranges mapped by a single kernel virtual address range.
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The kernel virtual address range starts at
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.Fa buf
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and is
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.Fa len
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bytes long.
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The
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.Fa mflags
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argument can be set to either
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.Dv M_NOWAIT
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or
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.Dv M_WAITOK .
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.Pp
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The
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.Nm sglist_clone
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function returns a copy of an existing scatter/gather list object
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.Fa sg .
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The
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.Fa mflags
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argument can be set to either
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.Dv M_NOWAIT
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or
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.Dv M_WAITOK .
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This can be used to obtain a private copy of a scatter/gather list before
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modifying it.
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.Pp
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The
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.Nm sglist_init
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function initializes a scatter/gather list header.
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The header is pointed to by
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.Fa sg
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and is initialized to manage an array of
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.Fa maxsegs
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scatter/gather list elements pointed to by
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.Fa segs .
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This can be used to initialize a scatter/gather list header whose storage
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is not provided by
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.Nm sglist_alloc .
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In that case, the caller should not call
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.Nm sglist_free
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to release its own reference and is responsible for ensuring all other
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references to the list are dropped before it releases the storage for
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.Fa sg
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and
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.Fa segs .
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.Ss Constructing Scatter/Gather Lists
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The
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.Nm
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API provides several routines for building a scatter/gather list to describe
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one or more objects.
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Specifically, the
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.Nm sglist_append
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family of routines can be used to append the physical address ranges described
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by an object to the end of a scatter/gather list.
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All of these routines return 0 on success or an error on failure.
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If a request to append an address range to a scatter/gather list fails,
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the scatter/gather list will remain unchanged.
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.Pp
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The
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.Nm sglist_append
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function appends the physical address ranges described by a single kernel
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virtual address range to the scatter/gather list
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.Fa sg .
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The kernel virtual address range starts at
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.Fa buf
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and is
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.Fa len
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bytes long.
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.Pp
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The
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.Nm sglist_append_bio
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function appends the physical address ranges described by a single bio
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.Fa bp
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to the scatter/gather list
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.Fa sg .
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.Pp
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The
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.Nm sglist_append_mbuf
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function appends the physical address ranges described by an entire mbuf
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chain
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.Fa m
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to the scatter/gather list
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.Fa sg .
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.Pp
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The
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.Nm sglist_append_phys
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function appends a single physical address range to the scatter/gather list
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.Fa sg .
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The physical address range starts at
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.Fa paddr
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and is
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.Fa len
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bytes long.
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.Pp
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The
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.Nm sglist_append_uio
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function appends the physical address ranges described by a
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.Xr uio 9
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object to the scatter/gather list
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.Fa sg .
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Note that it is the caller's responsibility to ensure that the pages backing
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the I/O request are wired for the lifetime of
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.Fa sg .
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Note also that this routine does not modify
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.Fa uio .
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.Pp
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The
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.Nm sglist_append_user
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function appends the physical address ranges described by a single user
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virtual address range to the scatter/gather list
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.Fa sg .
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The user virtual address range is relative to the address space of the thread
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.Fa td .
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It starts at
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.Fa buf
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and is
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.Fa len
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bytes long.
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Note that it is the caller's responsibility to ensure that the pages backing
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the user buffer are wired for the lifetime of
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.Fa sg .
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.Pp
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The
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.Nm sglist_consume_uio
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function is a variation of
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.Nm sglist_append_uio .
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As with
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.Nm sglist_append_uio ,
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it appends the physical address ranges described by
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.Fa uio
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to the scatter/gather list
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.Fa sg .
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Unlike
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.Nm sglist_append_uio ,
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however,
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.Nm sglist_consume_uio
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modifies the I/O request to indicate that the appended address ranges have
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been processed similar to calling
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.Xr uiomove 9 .
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This routine will only append ranges that describe up to
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.Fa resid
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total bytes in length.
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If the available segments in the scatter/gather list are exhausted before
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.Fa resid
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bytes are processed,
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then the
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.Fa uio
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structure will be updated to reflect the actual number of bytes processed,
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and
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.Nm sglist_consume_io
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will return zero to indicate success.
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In effect, this function will perform partial reads or writes.
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The caller can compare the
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.Fa uio_resid
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member of
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.Fa uio
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before and after calling
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.Nm sglist_consume_uio
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to determine the actual number of bytes processed.
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.Ss Manipulating Scatter/Gather Lists
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The
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.Nm sglist_join
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function appends physical address ranges from the scatter/gather list
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.Fa second
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onto
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.Fa first
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and then resets
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.Fa second
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to an empty list.
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It returns zero on success or an error on failure.
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.Pp
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The
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.Nm sglist_split
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function splits an existing scatter/gather list into two lists.
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The first
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.Fa length
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bytes described by the list
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.Fa original
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are moved to a new list
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.Fa *head .
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If
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.Fa original
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describes a total address range that is smaller than
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.Fa length
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bytes,
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then all of the address ranges will be moved to the new list at
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.Fa *head
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and
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.Fa original
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will be an empty list.
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The caller may supply an existing scatter/gather list in
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.Fa *head .
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If so, the list must be empty.
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Otherwise, the caller may set
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.Fa *head
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to
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.Dv NULL
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in which case a new scatter/gather list will be allocated.
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In that case,
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.Fa mflags
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may be set to either
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.Dv M_NOWAIT
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or
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.Dv M_WAITOK .
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Note that since the
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.Fa original
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list is modified by this call, it must be a private list with no other
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references.
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The
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.Nm sglist_split
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function returns zero on success or an error on failure.
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.Pp
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The
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.Nm sglist_slice
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function generates a new scatter/gather list from a sub-range of an existing
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scatter/gather list
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.Fa original .
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The sub-range to extract is specified by the
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.Fa offset
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and
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.Fa length
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parameters.
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The new scatter/gather list is stored in
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.Fa *slice .
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As with
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.Fa head
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for
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.Nm sglist_join ,
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the caller may either provide an empty scatter/gather list,
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or it may set
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.Fa *slice
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to
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.Dv NULL
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in which case
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.Nm sglist_slice
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will allocate a new list subject to
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.Fa mflags .
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Unlike
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.Nm sglist_split ,
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.Nm sglist_slice
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does not modify
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.Fa original
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and does not require it to be a private list.
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The
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.Nm sglist_split
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function returns zero on success or an error on failure.
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.Ss Miscellaneous Routines
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The
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.Nm sglist_reset
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function clears the scatter/gather list
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.Fa sg
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so that it no longer maps any address ranges.
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This can allow reuse of a single scatter/gather list object for multiple
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requests.
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.Pp
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The
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.Nm sglist_length
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function returns the total length of the physical address ranges described
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by the scatter/gather list
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.Fa sg .
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.Sh RETURN VALUES
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The
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.Nm sglist_alloc ,
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.Nm sglist_build ,
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and
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.Nm sglist_clone
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functions return a new scatter/gather list on success or
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.Dv NULL
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on failure.
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.Pp
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The
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.Nm sglist_append
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family of functions and the
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.Nm sglist_consume_uio ,
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.Nm sglist_join ,
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.Nm sglist_slice ,
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and
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.Nm sglist_split
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functions return zero on success or an error on failure.
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.Pp
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The
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.Nm sglist_count
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function returns a count of scatter/gather list elements.
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.Pp
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The
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.Nm sglist_length
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function returns a count of address space described by a scatter/gather list
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in bytes.
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.Sh ERRORS
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The
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.Nm sglist_append
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functions return the following errors on failure:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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The scatter/gather list has zero segments.
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.It Bq Er EFBIG
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There are not enough available segments in the scatter/gather list to append
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the specified physical address ranges.
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.El
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.Pp
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The
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.Nm sglist_consume_uio
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function returns the following error on failure:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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The scatter/gather list has zero segments.
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.El
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.Pp
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The
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.Nm sglist_join
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function returns the following error on failure:
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.Bl -tag -width Er
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.It Bq Er EFBIG
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There are not enough available segments in the scatter/gather list
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.Fa first
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to append the physical address ranges from
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.Fa second .
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.El
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.Pp
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The
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.Nm sglist_slice
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function returns the following errors on failure:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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The
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.Fa original
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scatter/gather list does not describe enough address space to cover the
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requested sub-range.
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.It Bq Er EINVAL
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The caller-supplied scatter/gather list in
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.Fa *slice
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is not empty.
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.It Bq Er ENOMEM
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An attempt to allocate a new scatter/gather list with
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.Dv M_NOWAIT
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set in
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.Fa mflags
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failed.
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.It Bq Er EFBIG
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There are not enough available segments in the caller-supplied scatter/gather
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list in
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.Fa *slice
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to describe the requested physical address ranges.
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.El
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.Pp
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The
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.Nm sglist_split
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function returns the following errors on failure:
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.Bl -tag -width Er
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.It Bq Er EDOOFUS
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The
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.Fa original
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scatter/gather list has more than one reference.
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.It Bq Er EINVAL
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The caller-supplied scatter/gather list in
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.Fa *head
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is not empty.
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.It Bq Er ENOMEM
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An attempt to allocate a new scatter/gather list with
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.Dv M_NOWAIT
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set in
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.Fa mflags
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failed.
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.It Bq Er EFBIG
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There are not enough available segments in the caller-supplied scatter/gather
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list in
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.Fa *head
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to describe the requested physical address ranges.
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.El
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.Sh SEE ALSO
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.Xr g_bio 9 ,
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.Xr malloc 9 ,
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.Xr mbuf 9 ,
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.Xr uio 9
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.Sh HISTORY
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This API was first introduced in
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.Fx 8.0 .
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