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/*
* Oracle Linux DTrace.
* Copyright (c) 2025, Oracle and/or its affiliates. All rights reserved.
* Licensed under the Universal Permissive License v 1.0 as shown at
* http://oss.oracle.com/licenses/upl.
*/
/*
* NAME
* wrun.d - display arguments to write() for the w command
*
* SYNOPSIS
* sudo dtrace -s wrun.d
*
* DESCRIPTION
* Trace the calls to write(), but only when executed by the w
* command. For such calls, print the file descriptor, the
* output string, and the number of bytes printed.
*
* NOTES
* - Execute this script in the background, and type in "w", or
* run it in the foreground and type in "w" in a separate window.
*
* - The script needs to be terminated with ctrl-C. In case the
* script is running in the background, get it to run in the
* foreground first by using the fg command and then use ctrl-C
* to terminate the process. Otherwise, typing in ctrl-C will do.
*
* - DTrace has a default limit of 256 bytes for strings. In this
* example, the output string may be longer than this. If so,
* either use the "-x strsize=<new-length>" command line option,
* or a "#pragma D option strsize=<new-length>" pragma in the
* script to increase the size. The latter is shown below.
*/
#pragma D option strsize=512
/*
* Use a predicate to only execute the clause in case the w
* command causes the probe to fire.
*/
syscall::write:entry
/execname == "w"/
{
/*
* Use copyinstr() to copy the string from user space into a DTrace
* buffer in kernel space. This function returns a pointer to the buffer.
* The string it points to, is null terminated.
* The third argument in the call to write() is the number of bytes
* to be printed. This could be used as an optional second argument
* in copyinstr() so that only this many bytes are copied.
*/
printf("%s(fd=%d\noutput=\n%s\nbytes=%d)\n",probefunc, arg0,
copyinstr(arg1), arg2);
}
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