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.\" Copyright (c) 1991 The Regents of the University of California.
.\" 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.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by the University of
.\"	California, Berkeley and its contributors.
.\" 4. Neither the name of the University 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 REGENTS 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 REGENTS 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.
.\"
.\"	@(#)mem.4	5.3 (Berkeley) 5/2/91
.\" $FreeBSD$
.\"
.Dd May 2, 1991
.Dt MEM 4
.Os
.Sh NAME
.Nm mem ,
.Nm kmem
.Nd memory files
.Sh DESCRIPTION
The special file
.Pa /dev/mem
is an interface to the physical memory of the computer.
Byte offsets in this file are interpreted as physical memory addresses.
Reading and writing this file is equivalent to reading and writing
memory itself.
Only offsets within the bounds of
.Pa /dev/mem
are allowed.
.Pp
Kernel virtual memory is accessed through the interface
.Pa /dev/kmem
in the same manner as
.Pa /dev/mem .
Only kernel virtual addresses that are currently mapped to memory are allowed.
.Pp
On
.Tn ISA
the
.Tn I/O
memory space begins at physical address 0x000a0000
and runs to 0x00100000.
The
per-process data
size
for the current process
is
.Dv UPAGES
long, and ends at virtual
address 0xf0000000.
.Sh IOCTL INTERFACE
Several architectures allow attributes to be associated with ranges of physical
memory.
These attributes can be manipulated via
.Fn ioctl
calls performed on
.Pa /dev/mem .
Declarations and data types are to be found in
.Aq Pa sys/memrange.h .
.Pp
The specific attributes, and number of programmable ranges may vary between
architectures.
The full set of supported attributes is:
.Bl -tag -width indent
.It Dv MDF_UNCACHEABLE
The region is not cached.
.It Dv MDF_WRITECOMBINE
Writes to the region may be combined or performed out of order.
.It Dv MDF_WRITETHROUGH
Writes to the region are committed synchronously.
.It Dv MDF_WRITEBACK
Writes to the region are committed asynchronously.
.It Dv MDF_WRITEPROTECT
The region cannot be written to.
.El
.Pp
Memory ranges are described by
.Vt struct mem_range_desc :
.Bd -literal -offset indent
u_int64_t	mr_base;	/\(** physical base address \(**/
u_int64_t	mr_len;		/\(** physical length of region \(**/
int		mr_flags;	/\(** attributes of region \(**/
char		mr_owner[8];
.Ed
.Pp
In addition to the region attributes listed above, the following flags
may also be set in the
.Fa mr_flags
field:
.Bl -tag -width indent
.It MDF_FIXBASE
The region's base address cannot be changed.
.It MDF_FIXLEN
The region's length cannot be changed.
.It MDF_FIRMWARE
The region is believed to have been established by the system firmware.
.It MDF_ACTIVE
The region is currently active.
.It MDF_BOGUS
We believe the region to be invalid or otherwise erroneous.
.It MDF_FIXACTIVE
The region cannot be disabled.
.It MDF_BUSY
The region is currently owned by another process and may not be
altered.
.El
.Pp
Operations are performed using
.Fa struct mem_range_op :
.Bd -literal -offset indent
struct mem_range_desc	*mo_desc;
int			mo_arg[2];
.Ed
.Pp
The
.Dv MEMRANGE_GET
ioctl is used to retrieve current memory range attributes.
If
.Va mo_arg[0]
is set to 0, it will be updated with the total number of memory range
descriptors.
If greater than 0, the array at
.Va mo_desc
will be filled with a corresponding number of descriptor structures,
or the maximum, whichever is less.
.Pp
The
.Dv MEMRANGE_SET
ioctl is used to add, alter and remove memory range attributes.  A range
with the
.Dv MDF_FIXACTIVE
flag may not be removed; a range with the
.Dv MDF_BUSY
flag may not be removed or updated.
.Pp
.Va mo_arg[0]
should be set to
.Dv MEMRANGE_SET_UPDATE
to update an existing or establish a new range, or to
.Dv MEMRANGE_SET_REMOVE
to remove a range.
.Sh RETURN VALUES
.Bl -tag -width Er
.It Bq Er EOPNOTSUPP
Memory range operations are not supported on this architecture.
.It Bq Er ENXIO
No memory range descriptors are available (eg. firmware has not enabled
any).
.It Bq Er EINVAL
The memory range supplied as an argument is invalid or overlaps another
range in a fashion not supported by this architecture.
.It Bq Er EBUSY
An attempt to remove or update a range failed because the range is busy.
.It Bq Er ENOSPC
An attempt to create a new range failed due to a shortage of hardware
resources (eg. descriptor slots).
.It Bq Er ENOENT
An attempt to remove a range failed because no range matches the descriptor
base/length supplied.
.It Bq Er EPERM
An attempt to remove a range failed because the range is permanently
enabled.
.El
.Sh BUGS
Busy range attributes are not yet managed correctly.
.Sh FILES
.Bl -tag -width /dev/kmem -compact
.It Pa /dev/mem
.It Pa /dev/kmem
.El
.Sh SEE ALSO
.Xr memcontrol 8
.Sh HISTORY
The
.Nm mem
and
.Nm kmem
files appeared in
.At v6 .
The ioctl interface for memory range attributes was added in
.Fx 3.2 .
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