179fa75e6e
Computing Technologies LLC to Hudson River Trading LLC. Approved by: Hudson River Trading LLC (who owns ACT LLC) MFC after: 1 week
187 lines
5.0 KiB
Groff
187 lines
5.0 KiB
Groff
.\"
|
|
.\" Copyright (c) 2011 Hudson River Trading LLC
|
|
.\" Written by: John H. Baldwin <jhb@FreeBSD.org>
|
|
.\" All rights reserved.
|
|
.\"
|
|
.\" 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.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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.
|
|
.\"
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd December 14, 2011
|
|
.Dt SHM_MAP 9
|
|
.Os
|
|
.Sh NAME
|
|
.Nm shm_map , shm_unmap
|
|
.Nd "map shared memory objects into the kernel's address space"
|
|
.Sh SYNOPSIS
|
|
.In sys/types.h
|
|
.In sys/mman.h
|
|
.Ft int
|
|
.Fn shm_map "struct file *fp" "size_t size" "off_t offset" "void **memp"
|
|
.Ft int
|
|
.Fn shm_unmap "struct file *fp" "void *mem" "size_t size"
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Fn shm_map
|
|
and
|
|
.Fn shm_unmap
|
|
functions provide an API for mapping shared memory objects into the kernel.
|
|
Shared memory objects are created by
|
|
.Xr shm_open 2 .
|
|
These objects can then be passed into the kernel via file descriptors.
|
|
.Pp
|
|
A shared memory object cannot be shrunk while it is mapped into the kernel.
|
|
This is to avoid invalidating any pages that may be wired into the kernel's
|
|
address space.
|
|
Shared memory objects can still be grown while mapped into the kernel.
|
|
.Pp
|
|
To simplify the accounting needed to enforce the above requirement,
|
|
callers of this API are required to unmap the entire region mapped by
|
|
.Fn shm_map
|
|
when calling
|
|
.Fn shm_unmap .
|
|
Unmapping only a portion of the region is not permitted.
|
|
.Pp
|
|
The
|
|
.Fn shm_map
|
|
function locates the shared memory object associated with the open file
|
|
.Fa fp .
|
|
It maps the region of that object described by
|
|
.Fa offset
|
|
and
|
|
.Fa size
|
|
into the kernel's address space.
|
|
If it succeeds,
|
|
.Fa *memp
|
|
will be set to the start of the mapping.
|
|
All pages for the range will be wired into memory upon successful return.
|
|
.Pp
|
|
The
|
|
.Fn shm_unmap
|
|
function unmaps a region previously mapped by
|
|
.Fn shm_map .
|
|
The
|
|
.Fa mem
|
|
argument should match the value previously returned in
|
|
.Fa *memp ,
|
|
and the
|
|
.Fa size
|
|
argument should match the value passed to
|
|
.Fn shm_map .
|
|
.Pp
|
|
Note that
|
|
.Fn shm_map
|
|
will not hold an extra reference on the open file
|
|
.Fa fp
|
|
for the lifetime of the mapping.
|
|
Instead,
|
|
the calling code is required to do this if it wishes to use
|
|
.Fn shm_unmap
|
|
on the region in the future.
|
|
.Sh RETURN VALUES
|
|
The
|
|
.Fn shm_map
|
|
and
|
|
.Fn shm_unmap
|
|
functions return zero on success or an error on failure.
|
|
.Sh EXAMPLES
|
|
The following function accepts a file descriptor for a shared memory
|
|
object.
|
|
It maps the first sixteen kilobytes of the object into the kernel,
|
|
performs some work on that address,
|
|
and then unmaps the address before returning.
|
|
.Bd -literal -offset indent
|
|
int
|
|
shm_example(int fd)
|
|
{
|
|
struct file *fp;
|
|
void *mem;
|
|
int error;
|
|
|
|
error = fget(curthread, fd, CAP_MMAP, &fp);
|
|
if (error)
|
|
return (error);
|
|
error = shm_map(fp, 16384, 0, &mem);
|
|
if (error) {
|
|
fdrop(fp, curthread);
|
|
return (error);
|
|
}
|
|
|
|
/* Do something with 'mem'. */
|
|
|
|
error = shm_unmap(fp, mem, 16384);
|
|
fdrop(fp, curthread);
|
|
return (error);
|
|
}
|
|
.Ed
|
|
.Sh ERRORS
|
|
The
|
|
.Fn shm_map
|
|
function returns the following errors on failure:
|
|
.Bl -tag -width Er
|
|
.It Bq Er EINVAL
|
|
The open file
|
|
.Fa fp
|
|
is not a shared memory object.
|
|
.It Bq Er EINVAL
|
|
The requested region described by
|
|
.Fa offset
|
|
and
|
|
.Fa size
|
|
extends beyond the end of the shared memory object.
|
|
.It Bq Er ENOMEM
|
|
Insufficient address space was available.
|
|
.It Bq Er EACCES
|
|
The shared memory object could not be mapped due to a protection error.
|
|
.It Bq Er EINVAL
|
|
The shared memory object could not be mapped due to some other VM error.
|
|
.El
|
|
.Pp
|
|
The
|
|
.Fn shm_unmap
|
|
function returns the following errors on failure:
|
|
.Bl -tag -width Er
|
|
.It Bq Er EINVAL
|
|
The open file
|
|
.Fa fp
|
|
is not a shared memory object.
|
|
.It Bq Er EINVAL
|
|
The address range described by
|
|
.Fa mem
|
|
and
|
|
.Fa size
|
|
is not a valid address range.
|
|
.It Bq Er EINVAL
|
|
The address range described by
|
|
.Fa mem
|
|
and
|
|
.Fa size
|
|
is not backed by the shared memory object associated with the open file
|
|
.Fa fp ,
|
|
or the address range does not cover the entire mapping of the object.
|
|
.El
|
|
.Sh SEE ALSO
|
|
.Xr shm_open 2
|
|
.Sh HISTORY
|
|
This API was first introduced in
|
|
.Fx 10.0 .
|