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 or /dev/xf86. 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 {
	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];
};

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.

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 structures, 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.

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.