143 lines
4.4 KiB
Groff
143 lines
4.4 KiB
Groff
.\"
|
|
.\" Copyright (c) 2007 Seccuris Inc.
|
|
.\" All rights reserved.
|
|
.\"
|
|
.\" This documentation was written by Robert N. M. Watson under contract to
|
|
.\" Seccuris Inc.
|
|
.\"
|
|
.\" 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(s), this list of conditions and the following disclaimer as
|
|
.\" the first lines of this file unmodified other than the possible
|
|
.\" addition of one or more copyright notices.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice(s), this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``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 COPYRIGHT HOLDER(S) 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.
|
|
.\"
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd January 28, 2007
|
|
.Dt SF_BUF 9
|
|
.Os
|
|
.Sh NAME
|
|
.Nm sf_buf
|
|
.Nd manage temporary kernel address space mapping for memory pages
|
|
.Sh SYNOPSIS
|
|
.In sys/sf_buf.h
|
|
.Ft struct sf_buf *
|
|
.Fn sf_buf_alloc "struct vm_page *m" "int flags"
|
|
.Ft void
|
|
.Fn sf_buf_free "struct sf_buf *sf"
|
|
.Ft vm_offset_t
|
|
.Fn sf_buf_kva "struct sf_buf *sf"
|
|
.Ft struct vm_page *
|
|
.Fn sf_buf_page "struct sf_buf *sf"
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Nm
|
|
interface, historically the
|
|
.Xr sendfile 2
|
|
buffer interface, allows kernel subsystems to manage temporary kernel address
|
|
space mappings for physical memory pages.
|
|
On systems with a direct memory map region (allowing all physical pages to be
|
|
visible in the kernel address space at all times), the
|
|
.Vt "struct sf_buf"
|
|
will point to an address in the direct map region; on systems without a
|
|
direct memory map region, the
|
|
.Vt "struct sf_buf"
|
|
will manage a temporary kernel address space mapping valid for the lifetime
|
|
of the
|
|
.Vt "struct sf_buf".
|
|
.Pp
|
|
Call
|
|
.Fn sf_buf_alloc
|
|
to allocate a
|
|
.Vt "struct sf_buf"
|
|
for a physical memory page.
|
|
.Fn sf_buf_alloc
|
|
is not responsible for arranging for the page to be present in physical
|
|
memory; the caller should already have arranged for the page to be wired,
|
|
i.e., by calling
|
|
.Xr vm_page_wire 9 .
|
|
Several flags may be passed to
|
|
.Fn sf_buf_alloc :
|
|
.Bl -tag -width SFB_CPUPRIVATE
|
|
.It Dv SFB_CATCH
|
|
Cause
|
|
.Fn sf_buf_alloc
|
|
to abort and return
|
|
.Dv NULL
|
|
if a signal is received waiting for a
|
|
.Vt "struct sf_buf"
|
|
to become available.
|
|
.It Dv SFB_NOWAIT
|
|
Cause
|
|
.Fn sf_buf_alloc
|
|
to return
|
|
.Dv NULL
|
|
rather than sleeping if a
|
|
.Vt "struct sf_buf"
|
|
is not immediately available.
|
|
.It Dv SFB_CPUPRIVATE
|
|
Cause
|
|
.Fn sf_buf_alloc
|
|
to only arrange that the temporary mapping be valid on the current CPU,
|
|
avoiding unnecessary TLB shootdowns for mappings that will only be accessed
|
|
on a single CPU at a time.
|
|
The caller must ensure that accesses to the virtual address occur only on the
|
|
CPU from which
|
|
.Fn sf_buf_alloc
|
|
was invoked, perhaps by using
|
|
.Fn sched_pin .
|
|
.El
|
|
.Pp
|
|
Call
|
|
.Fn sf_buf_kva
|
|
to return a kernel mapped address for the page.
|
|
.Pp
|
|
Call
|
|
.Fn sf_buf_page
|
|
to return a pointer to the page originally passed into
|
|
.Fn sf_buf_alloc .
|
|
.Pp
|
|
Call
|
|
.Fn sf_buf_free
|
|
to release the
|
|
.Vt "struct sf_buf"
|
|
reference.
|
|
The caller is responsible for releasing any wiring they have previously
|
|
acquired on the physical page;
|
|
.Fn sf_buf_free
|
|
releases only the temporary kernel address space mapping, not the page
|
|
itself.
|
|
.Pp
|
|
Uses of this interface include managing mappings of borrowed pages from user
|
|
memory, such as in zero-copy socket I/O, or pages of memory from the buffer
|
|
cache referenced by mbuf external storage for
|
|
.Xr sendfile 2 .
|
|
.Sh SEE ALSO
|
|
.Xr sendfile 2 ,
|
|
.Xr vm_page_wire 9
|
|
.Sh AUTHORS
|
|
.An -nosplit
|
|
The
|
|
.Vt "struct sf_buf"
|
|
API was designed and implemented by
|
|
.An Alan L. Cox .
|
|
This manual page was written by
|
|
.An Robert N. M. Watson .
|