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

     kvm_open, kvm_openfiles, kvm_close -- initialize kernel virtual memory

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

     kvm_close(kvm_t *kd);

     The functions kvm_open() and kvm_openfiles() return a descriptor used to
     access kernel virtual memory via the kvm(3) library routines.  Both
     active kernels and crash dumps are accessible through this interface.

     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-

     There are two open routines which differ only with respect to the error
     mechanism.  One provides backward compatibility with the SunOS kvm
     library, while the other provides an improved error reporting framework.

     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
     nature 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_openfiles() function provides BSD style error reporting.  Here,
     error messages are not printed out by the library.  Instead, the applica-
     tion 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 error.  Since
     kvm_geterr() requires a kvm descriptor, but the open routines return NULL
     on failure, kvm_geterr() cannot be used to get the error message if open
     fails.  Thus, kvm_openfiles() will place any error message in the errbuf
     argument.  This buffer should be _POSIX2_LINE_MAX characters large (from

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

     The kvm_close() function returns 0 on success and -1 on failure.

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

     There should not be two 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 6.2                    January 29, 2004                    FreeBSD 6.2


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