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KVM_OPEN(3)	       FreeBSD Library Functions Manual		   KVM_OPEN(3)

     kvm_open, kvm_open2, kvm_openfiles, kvm_close -- initialize kernel	vir-
     tual memory access

     Kernel Data Access	Library	(libkvm, -lkvm)

     #include <fcntl.h>
     #include <kvm.h>

     kvm_t *
     kvm_open(const char *execfile, const char *corefile,
	 const char *swapfile, int flags, const	char *errstr);

     kvm_t *
     kvm_open2(const char *execfile, const char	*corefile, int flags,
	 char *errbuf, int (*resolver)(const char *name, kvaddr_t *addr));

     kvm_t *
     kvm_openfiles(const char *execfile, const char *corefile,
	 const char *swapfile, int flags, char *errbuf);

     kvm_close(kvm_t *kd);

     The functions kvm_open(), kvm_open2(), and	kvm_openfiles()	return a de-
     scriptor used to access kernel virtual memory via the kvm(3) library rou-
     tines.  Both active kernels and crash dumps are accessible	through	this

     The execfile argument is the executable image of the kernel being exam-
     ined.  This file must contain a symbol table.  If this argument is	NULL,
     the currently running system is assumed, as determined from

     The corefile argument is the kernel memory	device file.  It can be	either
     /dev/mem or a crash dump core generated by	savecore(8).  If corefile is
     NULL, the default indicated by _PATH_MEM from <paths.h> is	used.  It can
     also be set to a special value /dev/null by utilities like	ps(1) that do
     not directly access kernel	memory.

     The swapfile argument is currently	unused.

     The flags argument	indicates read/write access as in open(2) and applies
     only to the core file.  Only O_RDONLY, O_WRONLY, and O_RDWR are permit-

     The kvm library provides two different error reporting mechanisms.	 One
     provides backward compatibility with the SunOS kvm	library, while the
     other provides an improved	error reporting	framework.  The	mechanism used
     by	a descriptor is	determined by the function used	to open	the descrip-

     The kvm_open() function is	the Sun	kvm compatible open call.  Here, the
     errstr argument indicates how errors should be handled.  If it is NULL,
     no	errors are reported and	the application	cannot know the	specific na-
     ture of the failed	kvm call.  If it is not	NULL, errors are printed to
     stderr with errstr	prepended to the message, as in	perror(3).  Normally,
     the name of the program is	used here.  The	string is assumed to persist
     at	least until the	corresponding kvm_close() call.

     The kvm_open2() and kvm_openfiles() functions provide BSD style error re-
     porting.  Here, error messages are	not printed out	by the library.	 In-
     stead, the	application obtains the	error message corresponding to the
     most recent kvm library call using	kvm_geterr() (see kvm_geterr(3)).  The
     results are undefined if the most recent kvm call did not produce an er-
     ror.  Since kvm_geterr() requires a kvm descriptor, but the open routines
     return NULL on failure, kvm_geterr() cannot be used to get	the error mes-
     sage if open fails.  Thus,	kvm_open2() and	kvm_openfiles()	will place any
     error message in the errbuf argument.  This buffer	should be
     _POSIX2_LINE_MAX characters large (from <limits.h>).

     The resolver argument points to a function	used by	the kvm	library	to map
     symbol names to kernel virtual addresses.	When the resolver function is
     called, name specifies the	requested symbol name.	If the function	is
     able to resolve the name to an address, the address should	be set in addr
     and the function should return zero.  If the function is not able to re-
     solve the name to an address, it should return a non-zero value.  When
     opening a native kernel image, resolver may be set	to NULL	to use an in-
     ternal function to	resolve	symbol names.  Non-native kernel images	(such
     as	when cross-debugging a crash dump) require a valid resolver.

     The kvm_open(), kvm_open2(), and kvm_openfiles() functions	return a de-
     scriptor to be used in all	subsequent kvm library calls.  The library is
     fully re-entrant.	On failure, NULL is returned, in which case
     kvm_open2() and kvm_openfiles() write the error message into errbuf.

     The kvm_close() function returns the value	0 if successful; otherwise the
     value -1 is returned and the global variable errno	is set to indicate the

     The kvm_close() function may fail and set the global variable errno for
     any of the	errors specified for close(2).

     The kvm_close() function may also fail and	set errno if:

     [EINVAL]		The value passed via kd	was NULL.

     close(2), open(2),	kvm(3),	kvm_getargv(3),	kvm_getenvv(3),	kvm_geterr(3),
     kvm_getprocs(3), kvm_native(3), kvm_nlist(3), kvm_read(3),	kvm_write(3),
     kmem(4), mem(4)

     There should not be three open calls.  The	ill-defined error semantics of
     the Sun library and the desire to have a backward-compatible library for
     BSD left little choice.

FreeBSD	13.0			March 20, 2017			  FreeBSD 13.0


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