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@(#)kvm_open.3 8.3 (Berkeley) 4/19/94
$FreeBSD$
.Dd January 29, 2004 .Dt KVM_OPEN 3 .Os .Sh NAME .Nm kvm_open , .Nm kvm_openfiles , .Nm kvm_close .Nd initialize kernel virtual memory access .Sh LIBRARY .Lb libkvm .Sh SYNOPSIS n fcntl.h n kvm.h .Ft kvm_t * .Fn kvm_open "const char *execfile" "const char *corefile" "const char *swapfile" "int flags" "const char *errstr" .Ft kvm_t * .Fn kvm_openfiles "const char *execfile" "const char *corefile" "const char *swapfile" "int flags" "char *errbuf" .Ft int .Fn kvm_close "kvm_t *kd" .Sh DESCRIPTION The functions .Fn kvm_open and .Fn kvm_openfiles return a descriptor used to access kernel virtual memory via the .Xr kvm 3 library routines. Both active kernels and crash dumps are accessible through this interface.
p The .Fa execfile argument is the executable image of the kernel being examined. This file must contain a symbol table. If this argument is .Dv NULL , the currently running system is assumed, as determined from .Xr getbootfile 3 .
p The .Fa corefile argument is the kernel memory device file. It can be either
a /dev/mem or a crash dump core generated by .Xr savecore 8 . If .Fa corefile is .Dv NULL , the default indicated by .Dv _PATH_MEM from n paths.h is used. It can also be set to a special value
a /dev/null by utilities like .Xr ps 1 that do not directly access kernel memory.
p The .Fa swapfile argument is currently unused.
p The .Fa flags argument indicates read/write access as in .Xr open 2 and applies only to the core file. Only .Dv O_RDONLY , .Dv O_WRONLY , and .Dv O_RDWR are permitted.
p 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.
p The .Fn kvm_open function is the Sun kvm compatible open call. Here, the .Fa errstr argument indicates how errors should be handled. If it is .Dv NULL , no errors are reported and the application cannot know the specific nature of the failed kvm call. If it is not .Dv NULL , errors are printed to .Dv stderr with .Fa errstr prepended to the message, as in .Xr perror 3 . Normally, the name of the program is used here. The string is assumed to persist at least until the corresponding .Fn kvm_close call.
p The .Fn kvm_openfiles function provides x style error reporting. Here, error messages are not printed out by the library. Instead, the application obtains the error message corresponding to the most recent kvm library call using .Fn kvm_geterr (see .Xr kvm_geterr 3 ) . The results are undefined if the most recent kvm call did not produce an error. Since .Fn kvm_geterr requires a kvm descriptor, but the open routines return .Dv NULL on failure, .Fn kvm_geterr cannot be used to get the error message if open fails. Thus, .Fn kvm_openfiles will place any error message in the .Fa errbuf argument. This buffer should be _POSIX2_LINE_MAX characters large (from <limits.h>). .Sh RETURN VALUES The .Fn kvm_open and .Fn kvm_openfiles functions both return a descriptor to be used in all subsequent kvm library calls. The library is fully re-entrant. On failure, .Dv NULL is returned, in which case .Fn kvm_openfiles writes the error message into .Fa errbuf .
p The .Fn kvm_close function returns 0 on success and -1 on failure. .Sh SEE ALSO .Xr open 2 , .Xr kvm 3 , .Xr kvm_getargv 3 , .Xr kvm_getenvv 3 , .Xr kvm_geterr 3 , .Xr kvm_getprocs 3 , .Xr kvm_nlist 3 , .Xr kvm_read 3 , .Xr kvm_write 3 , .Xr kmem 4 , .Xr mem 4 .Sh BUGS 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 x left little choice.