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MEM(4)		       FreeBSD Kernel Interfaces Manual			MEM(4)

NAME
     mem, kmem -- memory files

SYNOPSIS
     device mem

DESCRIPTION
     The special file /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 /dev/mem	are
     allowed.

     Kernel virtual memory is accessed through the interface /dev/kmem in the
     same manner as /dev/mem.  Only kernel virtual addresses that are cur-
     rently mapped to memory are allowed.

     On	ISA the	I/O memory space begins	at physical address 0x000a0000 and
     runs to 0x00100000.  The per-process data size for	the current process is
     UPAGES long, and ends at virtual address 0xf0000000.

IOCTL INTERFACE
     Several architectures allow attributes to be associated with ranges of
     physical memory.  These attributes	can be manipulated via ioctl() calls
     performed on /dev/mem.  Declarations and data types are to	be found in
     <sys/memrange.h>.

     The specific attributes, and number of programmable ranges	may vary
     between architectures.  The full set of supported attributes is:

     MDF_UNCACHEABLE
	     The region	is not cached.

     MDF_WRITECOMBINE
	     Writes to the region may be combined or performed out of order.

     MDF_WRITETHROUGH
	     Writes to the region are committed	synchronously.

     MDF_WRITEBACK
	     Writes to the region are committed	asynchronously.

     MDF_WRITEPROTECT
	     The region	cannot be written to.

     Memory ranges are described by struct mem_range_desc:

	   uint64_t	   mr_base;	   /* physical base address */
	   uint64_t	   mr_len;	   /* physical length of region	*/
	   int		   mr_flags;	   /* attributes of region */
	   char		   mr_owner[8];

     In	addition to the	region attributes listed above,	the following flags
     may also be set in	the mr_flags field:

     MDF_FIXBASE
	     The region's base address cannot be changed.

     MDF_FIXLEN
	     The region's length cannot	be changed.

     MDF_FIRMWARE
	     The region	is believed to have been established by	the system
	     firmware.

     MDF_ACTIVE
	     The region	is currently active.

     MDF_BOGUS
	     We	believe	the region to be invalid or otherwise erroneous.

     MDF_FIXACTIVE
	     The region	cannot be disabled.

     MDF_BUSY
	     The region	is currently owned by another process and may not be
	     altered.

     Operations	are performed using struct mem_range_op:

	   struct mem_range_desc   *mo_desc;
	   int			   mo_arg[2];

     The MEMRANGE_GET ioctl is used to retrieve	current	memory range
     attributes.  If 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
     mo_desc will be filled with a corresponding number	of descriptor struc-
     tures, or the maximum, whichever is less.

     The MEMRANGE_SET ioctl is used to add, alter and remove memory range
     attributes.  A range with the MDF_FIXACTIVE flag may not be removed; a
     range with	the MDF_BUSY flag may not be removed or	updated.

     mo_arg[0] should be set to	MEMRANGE_SET_UPDATE to update an existing or
     establish a new range, or to MEMRANGE_SET_REMOVE to remove	a range.

RETURN VALUES
     [EOPNOTSUPP]	Memory range operations	are not	supported on this
			architecture.

     [ENXIO]		No memory range	descriptors are	available (e.g.
			firmware has not enabled any).

     [EINVAL]		The memory range supplied as an	argument is invalid or
			overlaps another range in a fashion not	supported by
			this architecture.

     [EBUSY]		An attempt to remove or	update a range failed because
			the range is busy.

     [ENOSPC]		An attempt to create a new range failed	due to a
			shortage of hardware resources (e.g. descriptor
			slots).

     [ENOENT]		An attempt to remove a range failed because no range
			matches	the descriptor base/length supplied.

     [EPERM]		An attempt to remove a range failed because the	range
			is permanently enabled.

FILES
     /dev/mem
     /dev/kmem

SEE ALSO
     kvm(3), memcontrol(8)

HISTORY
     The mem and kmem files appeared in	Version	6 AT&T UNIX.  The ioctl	inter-
     face for memory range attributes was added	in FreeBSD 3.2.

BUGS
     Busy range	attributes are not yet managed correctly.

     This device is required for all users of kvm(3) to	operate.

FreeBSD	10.1			October	3, 2004			  FreeBSD 10.1

NAME | SYNOPSIS | DESCRIPTION | IOCTL INTERFACE | RETURN VALUES | FILES | SEE ALSO | HISTORY | BUGS

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