[Digikam-devel] [Bug 195202] New: thumbnail rename fails (cross-device link) and so cache doesn't work

[Jonathan Marten]

https://bugs.kde.org/show_bug.cgi?id=195202

           Summary: thumbnail rename fails (cross-device link) and so
                    cache doesn't work
           Product: digikam
           Version: unspecified
          Platform: Compiled Sources
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: NOR
         Component: general
        AssignedTo: digikam-devel at kde.org
        ReportedBy: jjm at keelhaul.me.uk


Version:           0.11.0-svn (rev.: 968562) (using Devel)
OS:                Linux
Installed from:    Compiled sources

Image thumbnails are generated initially to a temporary file, using
KTemporaryFile.  This places the thumbnail in a path of the form:

  /tmp/kde-USER/MD5-digikam-?PID.png

These are then intended to be saved in the user's freedesktop standard
thumbnail directory, ~/.thumbnails/large or ~/.thumbnails/normal.  Digikam
attempts to do this by a simple rename in  ThumbnailCreator::load(const
QString& path):

    if(savedCorrectly)
    {
        int ret = 0;
        Q_ASSERT(!tempFileName.isEmpty());

#if KDE_IS_VERSION(4,2,85)
        // KDE 4.3.0
        ret = KDE::rename(QFile::encodeName(tempFileName),
                          QFile::encodeName(thumbPath));
#else
        // KDE 4.2.x or 4.1.x
        ret = KDE_rename(QFile::encodeName(tempFileName),
                         QFile::encodeName(thumbPath));
#endif

        if (ret != 0)
        {
            kDebug(50003) << "Cannot rename thumb file (" << tempFileName <<
")" << endl;
            kDebug(50003) << "to (" << thumbPath << ")..." << endl;
        }
    }

Unfortunately the rename() will not work if the temporary file and the
destination thumbnail are on different file systems, which will typically be
the case on any sensible installation.  On digikam's stderr output each
thumbnail generates a message such as:

digikam(28782)/digikam (core) Digikam::ThumbnailCreator::load: Cannot rename
thumb file ( "/tmp/kde-jjm/35f7885fd5af2a4371b9ce90855e38a2-digikam-J28782.png"
)
digikam(28782)/digikam (core) Digikam::ThumbnailCreator::load: to (
"/home/jjm/.thumbnails/large/35f7885fd5af2a4371b9ce90855e38a2.png" )...

The effect for the user is that switching between folders and albums is very
slow, because the thumbnails need to be regenerated every time.  Another side
effect is that /tmp fills up with thumbnail files that are never deleted.

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