Overview

fstrace is a C library for Linux and macOS that provides a framework to trace a program execution.

Building

fstrace uses SCons and pkg-config for building and depends on the following libraries:

• fsdyn
• rotatable

Before building fsdyn for the first time, run

git submodule update --init

To build fstrace, run

scons [ prefix=<prefix> ]

from the top-level fstrace directory. The prefix argument is a directory, /usr/local by default, where the build system searches for fstrace dependencies and installs fstrace.

To install fstrace, run

sudo scons [ prefix=<prefix> ] install

Trace File Format

The trace file is a sequence of ASCII records. Each record has this format:

YYYY-MM-DD hh:mm:ss.dddddd <id> <format>\n

that is, the UTC timestamp followed by the id and expanded format as given in fstrace_declare() by user code.

Trace Event Format

Trace events are declared in user code with the fstrace_declare() function. The function has a format argument similar to (but not identical with) that in the standard printf(3) function:

Format directive	Output format Regex	Explanation
%%	%	percent
%d	-?[0-9]+	signed integer
%u	[0-9]+	unsigned integer
%x	[0-9a-f]+	unsigned hexadecimal
%64d	-?[0-9]+	signed integer
%64u	[0-9]+	unsigned integer
%64x	[0-9a-f]+	unsigned hexadecimal
%lld	-?[0-9]+	signed integer
%llu	[0-9]+	unsigned integer
%llx	[0-9a-f]+	unsigned hexadecimal
%z	-?[0-9]+	signed integer
%f	-?[0-9]+(\.[0-9]+)?(e[-+][0-9]+)+	floating-point
%b	true|false	boolean
%s	[-0-9A-Za-z"%./<>\^_`{|}~]*	URL-encoded string1
%S	[-0-9A-Za-z"%./<>\^_`{|}~]*	URL-encoded string1
%A	[-0-9A-Za-z"%./<>\^_`{|}~]*	URL-encoded string2
%B	([0-9a-f][0-9a-f])*	octet string
%P	[0-9]+	getpid()
%T	[0-9]+	pthread_self()
%F	[-0-9A-Za-z"%./<>\^_`{|}~]*	__FILE__
%L	[0-9]+	__LINE__
%e	[0-9A-Z]+	errno (symbol or number)
%E	[0-9A-Z]+	errno (symbol or number)
%p	[0-9a-f]+	pointer
%a	[-0-9A-Za-z"%./<>\^_`{|}~]*	network address3
%I	[-0-9A-Za-z"%./<>\^_`{|}~]*	URL-encoded string1
%J	\[([-0-9A-Za-z"%./<>\^_`{|}~]*)(,\1)*\]	list of URL-encoded strings4

1. The NUL character is illegal inside a string. The percent encoding %00 is reserved for the encoding of an omitted string (NULL pointer).

2. The NUL character is allowed inside the string.

3. Examples:

 AF_INET`127.0.0.1`12345
 AF_INET6`fe80::62b7:7d4a:ed95:922a`12345
 AF_UNIX`/var/run/syslog
 OTHER`ffeea1

4. Examples:

[]
[hello]
[hello,world]

Convention

The user code is advised to stick to format strings like this:

ICAP-ACCEPT RHOST=%s RPORT=%d CONN-ID=%d

where "ICAP-ACCEPT" is the id of the event. In particular, the format string must only contain printable, non-control ASCII characters (regular expression: [ -~]*).

The event id's of a single tracing component should have a common prefix to facilitate event filtering.