02-15-2002
Physical Memory
Hi,
My problem is next....
How can I work with physical memory in the Unix FreeBSD 2.2 or hight?
What is the "mem" & "kmem" drivers?
P.S./ writing device driver for UNIX FreeBSD 2.2
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0 0 0 28220616 1318888 15 143 0 0 0 0 0 253 2 15 0 5215 14989 5917 7 0 93
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mem(7D) Devices mem(7D)
NAME
mem, kmem, allkmem - physical or virtual memory access
SYNOPSIS
/dev/mem
/dev/kmem
/dev/allkmem
DESCRIPTION
The file /dev/mem is a special file that provides access to the physical memory of the computer.
The file /dev/kmem is a special file that provides access to the virtual address space of the operating system kernel, excluding memory
that is associated with an I/O device.
The file /dev/allkmem is a special file that provides access to the virtual address space of the operating system kernel, including memory
that is associated with an I/O device. You can use any of these devices to examine and modify the system.
Byte addresses in /dev/mem are interpreted as physical memory addresses. Byte addresses in /dev/kmem and /dev/allkmem are interpreted as
kernel virtual memory addresses. A reference to a non-existent location returns an error. See ERRORS for more information.
The file /dev/mem accesses physical memory; the size of the file is equal to the amount of physical memory in the computer. This size may
be larger than 4GB on a system running the 32-bit operating environment. In this case, you can access memory beyond 4GB using a series of
read(2) and write(2) calls, a pread64() or pwrite64() call, or a combination of llseek(2) and read(2) or write(2).
ERRORS
EFAULT Occurs when trying to write(2) a read-only location (allkmem), read(2) a write-only location (allkmem), or read(2) or
write(2) a non-existent or unimplemented location (mem, kmem, allkmem).
EIO Occurs when trying to read(2) or write(2) a memory location that is associated with an I/O device using the /dev/kmem spe-
cial file.
ENXIO Results from attempting to mmap(2) a non-existent physical (mem) or virtual (kmem, allkmem) memory address.
FILES
/dev/mem Provides access to the computer's physical memory.
/dev/kmem Provides access to the virtual address space of the operating system kernel, excluding memory that is associated with an
I/O device.
/dev/allkmem Provides access to the virtual address space of the operating system kernel, including memory that is associated with an
I/O device.
SEE ALSO
llseek(2), mmap(2), read(2), write(2)
WARNINGS
Using these devices to modify (that is, write to) the address space of a live running operating system or to modify the state of a
hardware device is extremely dangerous and may result in a system panic if kernel data structures are damaged or if device state is
changed.
SunOS 5.10 18 Feb 2002 mem(7D)