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kvm(3) [freebsd man page]

KVM(3)							   BSD Library Functions Manual 						    KVM(3)

kvm -- kernel memory interface LIBRARY
Kernel Data Access Library (libkvm, -lkvm) DESCRIPTION
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 sysctl(3) for some functions, and mem(4) and kmem(4) for other functions, while crash dumps can be examined via the core file generated by savecore(8). The interface behaves similarly 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. The kvm_open() function is first called to obtain a descriptor for all subsequent calls. COMPATIBILITY
The kvm interface was first introduced in SunOS. A considerable number of programs have been developed that use this interface, making back- ward 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 depen- dent. Finally, the Sun kvm error reporting semantics are poorly defined. The library can be configured either to print errors to stderr automati- cally, 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. SEE ALSO
kvm_close(3), kvm_getargv(3), kvm_getenvv(3), kvm_geterr(3), kvm_getfiles(3), kvm_getloadavg(3), kvm_getprocs(3), kvm_getswapinfo(3), kvm_nlist(3), kvm_open(3), kvm_openfiles(3), kvm_read(3), kvm_write(3), sysctl(3), kmem(4), mem(4) BSD
April 25, 2010 BSD

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KVM_GETPROCS(3) 					   BSD Library Functions Manual 					   KVM_GETPROCS(3)

kvm_getprocs, kvm_getargv, kvm_getenvv -- access user process state LIBRARY
Kernel Data Access Library (libkvm, -lkvm) SYNOPSIS
#include <kvm.h> #include <sys/param.h> #include <sys/sysctl.h> #include <sys/user.h> struct kinfo_proc * kvm_getprocs(kvm_t *kd, int op, int arg, int *cnt); char ** kvm_getargv(kvm_t *kd, const struct kinfo_proc *p, int nchr); char ** kvm_getenvv(kvm_t *kd, const struct kinfo_proc *p, int nchr); DESCRIPTION
The kvm_getprocs() function returns a (sub-)set of active processes in the kernel indicated by kd. The op and arg arguments constitute a predicate which limits the set of processes returned. The value of op describes the filtering predicate as follows: KERN_PROC_ALL all processes and kernel visible threads KERN_PROC_PROC all processes, without threads KERN_PROC_PID processes with process ID arg KERN_PROC_PGRP processes with process group arg KERN_PROC_SESSION processes with session arg KERN_PROC_TTY processes with TTY arg KERN_PROC_UID processes with effective user ID arg KERN_PROC_RUID processes with real user ID arg KERN_PROC_INC_THREAD modifier to return all kernel visible threads when filtering by process ID, process group, TTY, user ID, and real user ID The number of processes found is returned in the reference parameter cnt. The processes are returned as a contiguous array of kinfo_proc structures. This memory is locally allocated, and subsequent calls to kvm_getprocs() and kvm_close() will overwrite this storage. The kvm_getargv() function returns a null-terminated argument vector that corresponds to the command line arguments passed to process indi- cated by p. Most likely, these arguments correspond to the values passed to exec(3) on process creation. This information is, however, deliberately under control of the process itself. Note that the original command name can be found, unaltered, in the p_comm field of the process structure returned by kvm_getprocs(). The nchr argument indicates the maximum number of characters, including null bytes, to use in building the strings. If this amount is exceeded, the string causing the overflow is truncated and the partial result is returned. This is handy for programs like ps(1) and w(1) that print only a one line summary of a command and should not copy out large amounts of text only to ignore it. If nchr is zero, no limit is imposed and all argument strings are returned in their entirety. The memory allocated to the argv pointers and string storage is owned by the kvm library. Subsequent kvm_getprocs() and kvm_close(3) calls will clobber this storage. The kvm_getenvv() function is similar to kvm_getargv() but returns the vector of environment strings. This data is also alterable by the process. RETURN VALUES
The kvm_getprocs(), kvm_getargv(), and kvm_getenvv() functions return NULL on failure. SEE ALSO
kvm(3), kvm_close(3), kvm_geterr(3), kvm_nlist(3), kvm_open(3), kvm_openfiles(3), kvm_read(3), kvm_write(3) BUGS
These routines do not belong in the kvm interface. BSD
November 22, 2011 BSD

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