QSettings: use QSaveFile and QLockFile to write the settings

The old unix locking code is no longer working on unix since it locks on
a file descriptor, but QSaveFile creates a new file, and as a result we
get the lock on the wrong file. Also there is no need to keep the lock
held only for reading as QSaveFile is atomic. It just needs to be held
when doing a read before writing.

As a result, since we don't hold the same lock, there could be a race
with an application running an older version of Qt if they are writing
on the same configuration file.

[ChangeLog][QtCore][QSettings] Fixed data loss while writing the config
to the disk fails.

[ChangeLog][Important behavior changes] The locking mechanism inside
QSettings has changed and is no longer compatible with the one of
previous versions of Qt. There might be corruption if two applications
running different versions of Qt are writing to the same config file
at the same time. You must also now have write permissions in the
directory containing the settings file in order to write settings

Task-number: QTBUG-21739
Change-Id: I0844a5e96c8bc1e1222a3dac6cc48170ca77fe1b
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

0 files changed, 0 insertions, 0 deletions