QStorageInfo: Add support for obtaining subvolume names

[ChangeLog][QtCore][QStorageInfo] Added QStorageInfo::subvolume(), which
returns the name of the subvolume of a volume that was mounted, if one
was detected. This is currently implemented only for btrfs on Linux.

Change-Id: Ib57b52598e2f452985e9fffd1459f3145d733ce5
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/io/qstorageinfo.cpp

@@ -260,13 +260,33 @@ QByteArray QStorageInfo::fileSystemType() const
     devpath like \c /dev/sda0 for local storages. On Windows, it returns the UNC
     path starting with \c \\\\?\\ for local storages (in other words, the volume GUID).
 
-    \sa rootPath()
+    \sa rootPath(), subvolume()
 */
 QByteArray QStorageInfo::device() const
 {
     return d->device;
 }
 
+/*!
+    \since 5.8
+    Returns the subvolume name for this volume.
+
+    Some filesystem types allow multiple subvolumes inside one device, which
+    may be mounted in different paths. If the subvolume could be detected, it
+    is returned here. The format of the subvolume name is specific to each
+    filesystem type.
+
+    If this volume was not mounted from a subvolume of a larger filesystem or
+    if the subvolume could not be detected, this function returns an empty byte
+    array.
+
+    \sa device()
+*/
+QByteArray QStorageInfo::subvolume() const
+{
+    return d->subvolume;
+}
+
 /*!
     Returns the human-readable name of a filesystem, usually called \c label.
 

src/corelib/io/qstorageinfo.h

@@ -71,6 +71,7 @@ public:
 
     QString rootPath() const;
     QByteArray device() const;
+    QByteArray subvolume() const;
     QByteArray fileSystemType() const;
     QString name() const;
     QString displayName() const;
@@ -100,7 +101,7 @@ inline bool operator==(const QStorageInfo &first, const QStorageInfo &second)
 {
     if (first.d == second.d)
         return true;
-    return first.device() == second.device();
+    return first.device() == second.device() && first.rootPath() == second.rootPath();
 }
 
 inline bool operator!=(const QStorageInfo &first, const QStorageInfo &second)

src/corelib/io/qstorageinfo_p.h

@@ -85,6 +85,7 @@ protected:
 public:
     QString rootPath;
     QByteArray device;
+    QByteArray subvolume;
     QByteArray fileSystemType;
     QString name;
 

src/corelib/io/qstorageinfo_unix.cpp

@@ -120,6 +120,7 @@ public:
     inline QString rootPath() const;
     inline QByteArray fileSystemType() const;
     inline QByteArray device() const;
+    inline QByteArray options() const;
 private:
 #if defined(Q_OS_BSD4)
     QT_STATFSBUF *stat_buf;
@@ -133,6 +134,7 @@ private:
     QByteArray m_rootPath;
     QByteArray m_fileSystemType;
     QByteArray m_device;
+    QByteArray m_options;
 #elif defined(Q_OS_LINUX) || defined(Q_OS_HURD)
     FILE *fp;
     mntent mnt;
@@ -228,6 +230,11 @@ inline QByteArray QStorageIterator::device() const
     return QByteArray(stat_buf[currentIndex].f_mntfromname);
 }
 
+inline QByteArray QStorageIterator::options() const
+{
+    return QByteArray();
+}
+
 #elif defined(Q_OS_SOLARIS)
 
 static const char pathMounted[] = "/etc/mnttab";
@@ -301,6 +308,7 @@ inline bool QStorageIterator::next()
     m_device = data.at(0);
     m_rootPath = data.at(1);
     m_fileSystemType = data.at(2);
+    m_options = data.at(3);
 
     return true;
 }
@@ -320,6 +328,11 @@ inline QByteArray QStorageIterator::device() const
     return m_device;
 }
 
+inline QByteArray QStorageIterator::options() const
+{
+    return m_options;
+}
+
 #elif defined(Q_OS_LINUX) || defined(Q_OS_HURD)
 
 static const char pathMounted[] = "/etc/mtab";
@@ -363,6 +376,11 @@ inline QByteArray QStorageIterator::device() const
     return QByteArray(mnt.mnt_fsname);
 }
 
+inline QByteArray QStorageIterator::options() const
+{
+    return QByteArray(mnt.mnt_opts);
+}
+
 #elif defined(Q_OS_HAIKU)
 inline QStorageIterator::QStorageIterator()
 {
@@ -420,6 +438,11 @@ inline QByteArray QStorageIterator::device() const
     return m_device;
 }
 
+inline QByteArray QStorageIterator::options() const
+{
+    return QByteArray();
+}
+
 #else
 
 inline QStorageIterator::QStorageIterator()
@@ -455,8 +478,35 @@ inline QByteArray QStorageIterator::device() const
     return QByteArray();
 }
 
+inline QByteArray QStorageIterator::options() const
+{
+    return QByteArray();
+}
+
 #endif
 
+static QByteArray extractSubvolume(const QStorageIterator &it)
+{
+#ifdef Q_OS_LINUX
+    if (it.fileSystemType() == "btrfs") {
+        const QByteArrayList opts = it.options().split(',');
+        QByteArray id;
+        for (const QByteArray &opt : opts) {
+            static const char subvol[] = "subvol=";
+            static const char subvolid[] = "subvolid=";
+            if (opt.startsWith(subvol))
+                return std::move(opt).mid(strlen(subvol));
+            if (opt.startsWith(subvolid))
+                id = std::move(opt).mid(strlen(subvolid));
+        }
+
+        // if we didn't find the subvolume name, return the subvolume ID
+        return id;
+    }
+#endif
+    return QByteArray();
+}
+
 void QStorageInfoPrivate::initRootPath()
 {
     rootPath = QFileInfo(rootPath).canonicalFilePath();
@@ -483,6 +533,7 @@ void QStorageInfoPrivate::initRootPath()
             rootPath = mountDir;
             device = it.device();
             fileSystemType = fsName;
+            subvolume = extractSubvolume(it);
         }
     }
 }

tests/manual/qstorageinfo/printvolumes.cpp

@@ -48,11 +48,15 @@ void printVolumes(const QList<QStorageInfo> &volumes, int (*printer)(const char
         if (info.fileSystemType() != fsAndType)
             fsAndType += " (" + info.fileSystemType() + ')';
 
-        printf("%-19s R%c ", fsAndType.constData(), info.isReadOnly() ? 'O' : 'W');
+        printer("%-19s R%c ", fsAndType.constData(), info.isReadOnly() ? 'O' : 'W');
         if (fsAndType.size() > 19)
-            printf("\n%23s", "");
+            printer("\n%23s", "");
 
-        printf("%10llu %10llu %5u  ", info.bytesTotal() / 1024, info.bytesFree() / 1024, info.blockSize());
-        printf("%-16s %s\n", qPrintable(info.name()), qPrintable(info.rootPath()));
+        printer("%10llu %10llu %5u  ", info.bytesTotal() / 1024, info.bytesFree() / 1024, info.blockSize());
+        if (!info.subvolume().isEmpty())
+            printer("subvol=%-18s ", qPrintable(info.subvolume()));
+        else
+            printer("%-25s ", qPrintable(info.name()));
+        printer("%s\n", qPrintable(info.rootPath()));
     }
 }