Gamin the File Alteration Monitor

Debugging Gamin

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Debugging support in gamin:

Both the client and server side, if compiled with debug support accept an environment variable GAM_DEBUG which is set will make them report debugging informations to stdout.

Usually for debugging you also want to use a dedicated server process so setting the GAM_CLIENT_ID environment allows to ensure this. Usually one also want to keep control over the server lifetime and not have it exit automatically after 30 seconds without connection, there is a command line flag --notimeout to gam_server for this.

A typical example of a debugging session using 2 shells would be:

shell1: export GAM_DEBUG=
shell1: gam_server --notimeout test

to run the server in debug mode using the ID "test"

shell2: export GAM_DEBUG=
shell2: export GAM_CLIENT_ID=test
shell2: gamin_client

to run the client in a verbose session. It is perfectly possible to also run the client under a debugger, for the server it works too except the dnotify kernel interface uses a signal SIG33 which is trapped by gdb. To avoid this use the handle gdb instruction:

(gdb) handle SIG33 nostop
Signal        Stop      Print   Pass to program Description
SIG33         No        Yes     Yes             Real-time event 33

even better add it to your $HOME/.gdbinit .

Debugging a running program:

Both the gam_server and client of the gamin library can get switched dynamically to a debug mode by sending them a signal SIGUSR2. In that case the program or library switches to verbose debugging and outputs the traces to a new file /tmp/gamin_debug_XXXXXX . Sending the signal again to the application or the server should switch off debugging.

Debugging and testing client:

A debugging client program called testgam is also available in the tests subdirectory. It allow to use the interface and monitor the flow of event received. Here is an example of a session:

paphio:~/gamin/tests -> export GAMIN_DEBUG_SERVER="../server/gam_server"
paphio:~/gamin/tests -> ./testgam -
> connect test
connected to test

The environment variable can be used to specify the path to the server to run, then testgam is launched in interactive mode (argument - ) and the program is asked to connect to the server for session test (the server will be started on-demand by the library if needed).

> mkdir temp
mkdir temp
> mkfile temp/foo
mkfile temp/foo
> mondir temp
mondir temp 0
1: /u/veillard/gamin/tests/temp Exists: NULL
1: foo Exists: NULL
1: /u/veillard/gamin/tests/temp EndExist: NULL
> mkfile temp/bar
mkfile temp/bar
1: bar Created: NULL
> rmfile temp/foo
rmfile temp/foo
1: foo Deleted: NULL

In this example a new directory is created with a file in it and then monitored, then the directory content is modified. The testgam program also poll and report events coming from the server as they arrive.

Daniel Veillard