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.\" Copyright (c) 2012
.\" David E. O'Brien <obrien@FreeBSD.org>. All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\" must display the following acknowledgment:
.\" This product includes software developed by David E. O'Brien and
.\" contributors.
.\" 4. Neither the name of the author nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANT ABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" $FreeBSD$
.\"
.Dd June 15, 2019
.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
.Nm
is not intended to be a security auditing tool.
Many system calls are not tracked and binaries of foreign ABI will not be fully
audited.
It is intended for auditing of processes for the purpose of determining its
dependencies in an efficient and easily parsable format.
An example of this is
.Xr make 1
which uses this module with
.Sy .MAKE.MODE=meta
to handle incremental builds more smartly.
.Pp
System calls are denoted using the following single letters:
.Pp
.Bl -tag -width indent -compact
.It Ql A
.Xr openat 2 .
The next log entry may be lacking an absolute path or be inaccurate.
.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
.It Ql M
.Xr rename 2
.It Ql R
.Xr open 2
or
.Xr openat 2
for read
.It Ql W
.Xr open 2
or
.Xr openat 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 separate
.Xr open 2
calls, one for
.Ql R
and one for
.Ql W .
Note that only successful system calls are captured.
.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.
This should normally be done under the control of a parent in the child after
.Xr fork 2
but before anything else.
See the example below.
.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 ERRORS
The
.Fn ioctl
system call
with
.Dv FILEMON_SET_FD
will fail if:
.Bl -tag -width Er
.It Bq Er EEXIST
The
.Nm
handle is already associated with a file descriptor.
.El
.Pp
The
.Fn ioctl
system call
with
.Dv FILEMON_SET_PID
will fail if:
.Bl -tag -width Er
.It Bq Er ESRCH
No process having the specified process ID exists.
.It Bq Er EBUSY
The process ID specified is already being traced and was not the current
process.
.El
.Pp
The
.Fn close
system call on the filemon file descriptor may fail with the errors from
.Xr write 2
if any error is encountered while writing the log.
It may also fail if:
.Bl -tag -width Er
.It Bq Er EFAULT
An invalid address was used for a traced system call argument, resulting in
no log entry for the system call.
.It Bq Er ENAMETOOLONG
An argument for a traced system call was too long, resulting in
no log entry for the system call.
.El
.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>
#include <unistd.h>
static void
open_filemon(void)
{
pid_t child;
int fm_fd, fm_log;
if ((fm_fd = open("/dev/filemon", O_RDWR | O_CLOEXEC)) == -1)
err(1, "open(\e"/dev/filemon\e", O_RDWR)");
if ((fm_log = open("filemon.out",
O_CREAT | O_WRONLY | O_TRUNC | O_CLOEXEC, 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");
if ((child = fork()) == 0) {
child = getpid();
if (ioctl(fm_fd, FILEMON_SET_PID, &child) == -1)
err(1, "Cannot set filemon PID");
/* Do something here. */
} else {
wait(&child);
close(fm_fd);
}
}
.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 script 1 ,
.Xr truss 1 ,
.Xr ioctl 2
.Sh HISTORY
A
.Nm
device appeared in
.Fx 9.1 .
.Sh BUGS
Unloading the module may panic the system, thus requires using
.Ic kldunload -f .
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