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.\"	David E. O'Brien <obrien@FreeBSD.org>.  All rights reserved.
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.\" $FreeBSD: release/9.1.0/share/man/man4/filemon.4 237795 2012-06-29 15:57:25Z obrien $
.\"
.Dd May 30, 2012
.Dt FILEMON 4
.Os
.Sh NAME
.Nm filemon
.Nd the filemon device
.Sh SYNOPSIS
.In dev/filemon/filemon.h
.Sh DESCRIPTION
The
.Nm
device allows a process to collect file operations data of its children.
The device
.Pa /dev/filemon
responds to two
.Xr ioctl 2
calls.
.Pp
System calls are denoted using the following single letters:
.Pp
.Bl -tag -width indent -compact
.It Ql C
.Xr chdir 2
.It Ql D
.Xr unlink 2
.It Ql E
.Xr exec 2
.It Ql F
.Xr fork 2 ,
.Xr vfork 2
.It Ql L
.Xr link 2 ,
.Xr linkat 2 ,
.Xr symlink 2 ,
.Xr symlinkat 2
.It Ql M
.Xr rename 2
.It Ql R
.Xr open 2
for read
.It Ql S
.Xr stat 2
.It Ql W
.Xr open 2
for write
.It Ql X
.Xr _exit 2
.El
.Pp
Note that
.Ql R
following
.Ql W
records can represent a single
.Xr open 2
for R/W,
or two seperate
.Xr open 2
calls, one for
.Ql R
and one for
.Ql W .
.Sh IOCTLS
User mode programs communicate with the
.Nm
driver through a number of ioctls which are described below.
Each takes a single argument.
.Bl -tag -width ".Dv FILEMON_SET_PID"
.It Dv FILEMON_SET_FD
Write the internal tracing buffer to the supplied open file descriptor.
.It Dv FILEMON_SET_PID
Child process ID to trace.
.El
.Sh RETURN VALUES
.\" .Rv -std ioctl
The
.Fn ioctl
function returns the value 0 if successful;
otherwise the value \-1 is returned and the global variable
.Va errno
is set to indicate the error.
.Sh FILES
.Bl -tag -width ".Pa /dev/filemon"
.It Pa /dev/filemon
.El
.Sh EXAMPLES
.Bd -literal
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <sys/ioctl.h>
#include <dev/filemon/filemon.h>
#include <fcntl.h>
#include <err.h>

static void
open_filemon(void)
{
	pid_t child;
	int fm_fd, fm_log;

	if ((fm_fd = open("/dev/filemon", O_RDWR)) == -1)
		err(1, "open(\e"/dev/filemon\e", O_RDWR)");
	if ((fm_log = open("filemon.out",
	    O_CREAT | O_WRONLY | O_TRUNC, DEFFILEMODE)) == -1)
		err(1, "open(filemon.out)");

	if (ioctl(fm_fd, FILEMON_SET_FD, &fm_log) == -1)
		err(1, "Cannot set filemon log file descriptor");
	/* Set up these two fd's to close on exec. */
	(void)fcntl(fm_fd, F_SETFD, FD_CLOEXEC);
	(void)fcntl(fm_log, F_SETFD, FD_CLOEXEC);

	if ((child = fork()) == 0) {
		child = getpid();
		if (ioctl(fm_fd, FILEMON_SET_PID, &child) == -1)
			err(1, "Cannot set filemon PID");
		/* Do something here. */
		return 0;
	} else {
		wait(&child);
		close(fm_fd);
	}
	return 0;
}
.Ed
.Pp
Creates a file named
.Pa filemon.out
and configures the
.Nm
device to write the
.Nm
buffer contents to it.
.Sh SEE ALSO
.Xr dtrace 1 ,
.Xr ktrace 1 ,
.Xr truss 1
.Sh HISTORY
A
.Nm
device appeared in
.Fx 9.1 .