kvm - kernel memory interface
The kvm library provides a uniform interface for accessing
kernel virtual
memory images, including live systems and crash dumps. Access to live
systems is via /dev/mem while crash dumps can be examined
via the core
file generated by savecore(8). The interface behaves identically in both
cases. Memory can be read and written, kernel symbol addresses can be
looked up efficiently, and information about user processes
can be gathered.
kvm_open() is first called to obtain a descriptor for all
subsequent
calls.
/dev/mem interface to physical memory
kvm_close(3), kvm_getargv(3), kvm_getenvv(3), kvm_geterr(3),
kvm_getloadavg(3), kvm_getprocs(3), kvm_nlist(3),
kvm_open(3),
kvm_openfiles(3), kvm_read(3), kvm_write(3)
The kvm interface was first introduced in SunOS. A considerable number
of programs have been developed that use this interface,
making backward
compatibility highly desirable. In most respects, the Sun
kvm interface
is consistent and clean. Accordingly, the generic portion
of the interface
(i.e., kvm_open(), kvm_close(), kvm_read(),
kvm_write(), and
kvm_nlist()) has been incorporated into the BSD interface.
Indeed, many
kvm applications (i.e., debuggers and statistical monitors)
use only this
subset of the interface.
The process interface was not kept. This is not a portability issue
since any code that manipulates processes is inherently machine dependent.
Finally, the Sun kvm error reporting semantics are poorly
defined. The
library can be configured either to print errors to stderr
automatically,
or to print no error messages at all. In the latter case,
the nature of
the error cannot be determined. To overcome this, the BSD
interface includes
a routine, kvm_geterr(3), to return (not print out)
the error message
corresponding to the most recent error condition on the
given descriptor.
OpenBSD 3.6 June 4, 1993
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