QMYSQL driver not loaded - cross compiling for Raspberry PI 3

JarekT · 7 Jul 2020, 12:44

Dear All,

I'm cross compiling my project for Raspberry PI 3 and it successful except that I cannot connect to MySql database. I got this standard error:
QSqlDatabase: QMYSQL driver not loaded
QSqlDatabase: available drivers: QSQLITE QSQLITE2 QODBC QODBC3 QPSQL QPSQL7 QTDS QTDS7

Of course there are different threads that explain this but unfortunately this doesn't help...
My host: Ubuntu 18.04
Qt version that I use to cross compile for RPi3: 5.12.3
Target: Raspberry PI 3

Some time ago I was able to create the project (also on Ubuntu 18.04) and after some struggles I was able to connect to MySql. Unfortunately now I don't remember every single step I did... The project that I successfully run on the host, now I would like to run on RPi. I'm able to run the program on RPi but when I try to connect to the database I get the above error.

I understand I need to have libqsqlmysql.so library. Unfortunately I don't have it:

I downloaded sources for Qt5.12.3 from here. I understand I need to compile them so that I have the missing library. Am I right? Unfortunately I'm not able to do it.
Here are some outputs that I get:

Could you also explain me what is actually the difference in removing the problem for regular compilation and cross compilation? Shouldn't I prepare the mysql driver on the target rather than on the host?

I would be very happy to receive any suggestion...

KroMignon · 7 Jul 2020, 14:01

@JarekT said in QMYSQL driver not loaded - cross compiling for Raspberry PI 3:

I would be very happy to receive any suggestion...

First, I would suggest you to read documentation ==> https://doc.qt.io/qt-5/sql-driver.html#how-to-build-the-qmysql-plugin-on-unix-and-macos

Then, check MySQL or MariaDB shared libs and headers are installed on your platform.
Rerun qmake

JarekT · 7 Jul 2020, 14:41

@KroMignon Thank you for your reply. Please tell me should I do it on target or on the host?

The idea is to connect to the mysql installed on the target, so I think it should be done on the target. My MySQL database location is /var/lib, so I tried this:

but it looks like there is no qmake command available. I tried to find for any qmake file in the target:

KroMignon · 7 Jul 2020, 14:44

@JarekT said in QMYSQL driver not loaded - cross compiling for Raspberry PI 3:

Please tell me should I do it on target or on the host?

On the target of course.
Did you cross-compile Qt for you RPI or did you use a precompiled version?

JarekT · 7 Jul 2020, 14:53

@KroMignon I did cross-compile according to this procedure: LINK

KroMignon · J JarekT 7 Jul 2020, 14:44

This post is deleted!

KroMignon · 7 Jul 2020, 15:10

@JarekT So you have to add mysql libs on your RPI before creating the sysroot

on RPI

sudo apt-get install libmysqlclient-dev libmysqld-dev

After that you should be able to cross-compile the plugin

JarekT · 7 Jul 2020, 15:13

@KroMignon When I tried to install those packages I got information that mariadb counterparts are available. So I tried to install them and it appeared that libmariadb-dev-compat,libmariadb-dev I already had, but libmariadbd-dev I didn't have so I installed it.

How can I cross-compile the plugin?

KroMignon · 8 Jul 2020, 04:30

@JarekT said in QMYSQL driver not loaded - cross compiling for Raspberry PI 3:

How can I cross-compile the plugin?

After installing the missed packages, you have to recreate/update the sysroot.
Then restart qmake in the sqldrivers directory (I suppose RPI sysroot is located at /home/embsys/raspi/sysroot):

/home/embsys/raspi/qtbase/bin/qmake -- MYSQL_PREFIX=/home/embsys/raspi/sysroot/usr/local

make
make install

jsulm · wrote on 8 Jul 2020, 04:30

@KroMignon said in QMYSQL driver not loaded - cross compiling for Raspberry PI 3:

Then restart qmake in the sqldrivers directory

I would suggest to do out of source builds to avoid problems with build artefacts from previous builds.

JarekT · 8 Jul 2020, 06:58

@KroMignon said in QMYSQL driver not loaded - cross compiling for Raspberry PI 3:

you have to recreate/update the sysroot

In the ~/raspi folder I did this (192.168.0.100 is IP of RPi):
rsync -avz pi@192.168.0.100:/lib sysroot
rsync -avz pi@192.168.0.100:/usr/include sysroot/usr
rsync -avz pi@192.168.0.100:/usr/lib sysroot/usr
rsync -avz pi@192.168.0.100:/opt/vc sysroot/opt

Is this what you meant by "you have to recreate/update the sysroot"?

After that I did qmake and I got the following results:

Unfortunately I don't see that MySql was configured...

Is the prefix "MYSQL_PREFIX=/home/embsys/raspi/sysroot/usr/local" correct and is it enough?

@jsulm Before I did qmake I deleted whole src folder and extracted it again. Only then I did qmake. Is this what you meant?

KroMignon · 8 Jul 2020, 08:06

@JarekT said in QMYSQL driver not loaded - cross compiling for Raspberry PI 3:

Is the prefix "MYSQL_PREFIX=/home/embsys/raspi/sysroot/usr/local" correct and is it enough?

I don't really know, I don't have a RPI to test it.
But according to this post ==> https://raspberrypi.stackexchange.com/a/101366
You should probably use this:

/home/embsys/raspi/qtbase/bin/qmake -- MYSQL_PREFIX=/home/embsys/raspi/sysroot/usr/lib/arm-linux-gnueabihf

JarekT · 8 Jul 2020, 08:09

@KroMignon I've changed the prefix but looks like it didn't help..

What can I do "remove any leftovers from the previous build" before I do reconfiguration?

jsulm · 8 Jul 2020, 08:45

@JarekT said in QMYSQL driver not loaded - cross compiling for Raspberry PI 3:

What can I do "remove any leftovers from the previous build" before I do reconfiguration?

Extract again the source code. To avoid this do out of source builds:

mkdir build
cd build
qmake PATH_TO_SOURCE

JarekT · 8 Jul 2020, 09:04

@jsulm I've extracted again the sources. But I'm not sure if I understand what you meant by: "To avoid this do out of source builds". Do you mean that after I have newly extracted source code, I should always do the qmake in a new folder (eg. "build" as you mentioned) so that I do not affect the source code and in this way I can always do fresh compilation without the need to extract the source code files again?

Assuming that this is what you meant I did this:

As I can see mysql was not compiled... Could you please check if the paths and prefixes are correct?...

jsulm · 8 Jul 2020, 10:00

@JarekT said in QMYSQL driver not loaded - cross compiling for Raspberry PI 3:

I should always do the qmake in a new folder

Yes.

To check why it still does not work please see what is in configure.log file.

JarekT · 7 Aug 2020, 10:02

@jsulm Here is what I have in the config.log (I'm showing here only the part that contains information about the failures)

Could you please help me understand those problems?

KroMignon · 8 Jul 2020, 10:23

@JarekT said in QMYSQL driver not loaded - cross compiling for Raspberry PI 3:

Could you please help me understand those problems?

Can you says which is the local path where you have put the sysroot? I supposed it was /home/embsys/raspi/sysroot.
Then search in this path where is located libmysqlclient with find:

find /home/embsys/raspi/sysroot -name libmysqlclient*.*

Then use the path to configure/compile your plugin:

/home/embsys/raspi/qtbase/bin/qmake -- MYSQL_PREFIX=<lib_mysqlclient_path>

JarekT · wrote on 8 Jul 2020, 10:23

@KroMignon said in QMYSQL driver not loaded - cross compiling for Raspberry PI 3:

Can you says which is the local path where you have put the sysroot? I supposed it was /home/embsys/raspi/sysroot.

Yes, this is my sysroot. I did it as you can see below

This command I tried also before and the results are unsuccessful as before..
Here I'm configuring/compiling the plugin using sqldriver.pro file, but I also read somewhere that mysql.pro (/home/embsys/raspi/qt-everywhere-src-5.12.3/qtbase/src/plugins/sqldrivers/mysql/mysql.pro) file should compiled. Do you know anything about it?

JarekT · 7 Aug 2020, 11:04

Another idea: shouldn't I configure qmake itself before I try to use it to compile the plugin?

That was my configure command when I was doing cross-compiling configuration (as in the LINK)

./configure -release -opengl es2 -device linux-rasp-pi3-g++ -device-option CROSS_COMPILE=~/raspi/tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian-x64/bin/arm-linux-gnueabihf- -sysroot ~/raspi/sysroot -opensource -confirm-license -make libs -prefix /usr/local/qt5pi -extprefix ~/raspi/qt5pi -hostprefix ~/raspi/qt5 -no-use-gold-linker -v -no-gbm

The above doesn't include mysql feature (should it??)