View source for Guidelines and HOWTOs/Debugging/Debugging IOSlaves

This page describes how you can debug a KIO ioslave.

==How to Get Debug Output==

=== GUI (Qt5/KF5 instructions) ===

# Launch the  <code>kdebugsettings</code> tool, either from terminal or from KRunner (the latter can be invoked with Alt + F2)
# Type the name of the KIO Slave (e.g. ftp, http, ...). (If it's not listed, it doesn't use categorized debug output, so either its output is always on, or commented out in the code, in which case it needs to be ported to qCDebug)
# From the drop-down menu next to each KIO Slave you're interested in, select '''Full Debug'''
# Press '''OK''' to close the dialog and the save your changes
# You can either run <code>kdeinit5</code> in terminal, in which case the output from any IO slave that's started afterwards will show up in that terminal  OR
# Alternatively log out  then log back in, and additional debug info will typically end up in ~/.X.err, ~/.xsession-errors or ~/.local/share/sddm/xorg-session.log

Notes:
* If you have rebuilt an IO Slave from source with some changes you'll need ensure that <code>kdeinit5</code> will pick it up; this works with KIO from the KDE repos:
{{Input|1=<nowiki>
cd <path to build dir>/bin
export LD_LIBRARY_PATH=$PWD
export QT_PLUGIN_PATH=$PWD
kdeinit5</nowiki>}}
** in the first <code>cd</code> command you change to the directory containing the compiled binaries, in KIO case it's ''<build dir>/bin''.

* Instead of using <code>kdebugsettings</code>, you can change the Qt logging categories rules temporarily, in terminal:
{{Input|1=<nowiki>
export QT_LOGGING_RULES="*kio*=true"
</nowiki>}} 
** for more information see [https://doc.qt.io/qt-5/qloggingcategory.html this]. 
=== GUI (Qt4/kdelibs4 instructions) ===

# Press ALT+F2.
# Enter 'kdebugdialog --fullmode' without the quotes and press enter.
# Select the desired number in the "Debug area", e.g. 7103 for http.
# In the [Information] box, select "File" as the output.
# Enter the desired file name, e.g. /tmp/kio_http.log.
# Press OK to close the dialog.
# Press ALT+F2, type ''kdeinit4'' and press enter or alternatively log out of KDE and log back in.

This will print additional debug info to the stderr of your kdeinit process, which typically ends up in ~/.X.err, ~/.xsession-errors or ~/.local/share/sddm/xorg-session.log

===Manual (Qt4/kdelibs4 instructions)===
It is useful to redirect the debug output of your particular slave to a file 
instead of stderr. E.g. I myself use the following lines in
$KDEDIR/share/config/kdebugrc.
<pre>
[7113]
InfoOutput=0
InfoFilename=/tmp/http
[7103]
InfoOutput=0
InfoFilename=/tmp/http 
</pre>
This redirects all debug info for areas 7103 and 7113 (as used by kio_http) 
to the file /tmp/http.

To get debug information from the SMB slave you can add the following to
kioslaverc:
<pre>
[SMB]
DebugLevel=100
</pre>
This will print additional debug info to the stderr of your kdeinit process,
which typically ends up in ~/.X.err, ~/.xsession-errors or ~/.local/share/sddm/xorg-session.log

==How does an io-slave get started?==

Your application requests 'klauncher' via DBus for a slave. If 'klauncher' does not have an idle slave ready, it will ask kdeinit to start a new one. kdeinit forks and dlopens the library that contains the io-slave.
Then it calls a function called kdemain() in the library.

==Attaching gdb to an io-slave==
Due to the above sequence it is rather hard to get an io-slave in your
debugger. But wait there is hope. You can start <tt>klauncher</tt> in such a way
that slaves for a certain protocol (the first parameter of KIO::SlaveBase() constructor of the slave class) are started in debug mode.

E.g. to start all 'http' slaves in debug mode, you type:
<pre>
KDE_SLAVE_DEBUG_WAIT=http kdeinit5
</pre>

This will restart 'kdeinit' and 'klauncher'.

Note:
The string after the equal signal designates the name of a service, not the name of the slave! E.g. if you want to debug the kio_imap4, you must use:
<pre>
KDE_SLAVE_DEBUG_WAIT=imap kdeinit5
</pre>

For example, these commands don't work:
<pre>
KDE_SLAVE_DEBUG_WAIT=imap4 kdeinit5
KDE_SLAVE_DEBUG_WAIT=143 kdeinit5
</pre>

When your application now requests a http slave, the slave will be started
by kdeinit, but before it calls kdemain() (cq. main()) it will suspend the
slave by sending it a SIGSTOP signal.

In the terminal from which you started kdeinit you will get the following
message:
<pre>
kdeinit: Suspending process
kdeinit: 'gdb kdeinit 16779' to debug
kdeinit: 'kill -SIGCONT 16779' to continue
</pre>

You can now debug your slave by typing (or pasting) 'gdb kdeinit 16779' in
a terminal. 

Note that modern linux kernels disable ptrace. If gdb says "ptrace: Operation not permitted." then you need this:

<pre>echo 0 | sudo tee /proc/sys/kernel/yama/ptrace_scope</pre>

If you don't want to debug a slave you can let it continue by
sending it a SIGCONT by typing 'kill -SIGCONT 16779'.
Be aware that slaves will not be killed while they are suspended.

Once you have started gdb, you can set e.g. breakpoints and then resume the 
slave by typing 'continue'. The debugger will return immediate with a message 
that a SIGSTOP has been received so you will have to type 'continue' a second 
time.

See also [[Development/Tutorials/Debugging/Debugging_on_MS_Windows#Debugging_kioslaves|Windows-specific notes on debugging io-slaves]].

==Debugging io-slaves with valgrind==
KLauncher can be told to run certain io-slaves through valgrind. The following
command can be used to let klauncher run all https io-slaves via valgrind:
<pre>
KDE_SLAVE_VALGRIND=https kdeinit5
</pre>

The valgrind output will appear as the stderr output of the kdeinit process.
The $VALGRIND_OPTS environment variable can be used to pass options to valgrind.
If you want to use a different skin:
<pre>
KDE_SLAVE_VALGRIND_SKIN=callgrind      ( for example )
</pre>

== specific kioslaves ==
* [[Guidelines_and_HOWTOs/Debugging/Debugging IOSlaves/Debugging kio_fish|kio_fish]]
* [[Guidelines_and_HOWTOs/Debugging/Debugging IOSlaves/Debugging kio_sftp|kio_sftp]]
* [[Guidelines_and_HOWTOs/Debugging/Debugging IOSlaves/Debugging kio_smb|kio_smb]]