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MEM(4) | Device Drivers 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 currently 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 isUPAGES
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 viaioctl
() 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.
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];
- 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.
struct mem_range_desc *mo_desc; int mo_arg[2];
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; 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¶
Themem
and
kmem
files appeared in
Version 6 AT&T UNIX. The ioctl interface
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.October 3, 2004 | Debian |