Display usage of encrypted file systems (#760080)

There is already the set of methods in the Partition class to report the
file system usage.  Virtualise them and provide PartitionLUKS specific
implementations to calculate the usage of a file system wrapped in LUKS
encryption.

See the ascii art and comment in PartitionLUKS.cc for the details of
those calculations.

Bug 760080 - Implement read-only LUKS support

include/Partition.h

@@ -82,11 +82,11 @@ public:
 	          bool busy );
 
 	void set_sector_usage( Sector sectors_fs_size, Sector sectors_fs_unused ) ;
-	bool sector_usage_known() const ;
-	Sector estimated_min_size() const ;
-	Sector get_sectors_used() const ;
-	Sector get_sectors_unused() const ;
-	Sector get_sectors_unallocated() const ;
+	virtual bool sector_usage_known() const;
+	virtual Sector estimated_min_size() const;
+	virtual Sector get_sectors_used() const;
+	virtual Sector get_sectors_unused() const;
+	virtual Sector get_sectors_unallocated() const;
 	void get_usage_triple( int imax, int & i1, int & i2, int & i3 ) const ;
 
 	void Set_Unallocated( const Glib::ustring & device_path,

include/PartitionLUKS.h

@@ -34,6 +34,11 @@ public:
 	Partition & get_encrypted()              { return encrypted; };
 	const Partition & get_encrypted() const  { return encrypted; };
 
+	virtual bool sector_usage_known() const;
+	virtual Sector estimated_min_size() const;
+	virtual Sector get_sectors_used() const;
+	virtual Sector get_sectors_unused() const;
+	virtual Sector get_sectors_unallocated() const;
 	virtual Glib::ustring get_filesystem_label() const;
 
 private:

src/PartitionLUKS.cc

@@ -37,6 +37,110 @@ PartitionLUKS * PartitionLUKS::clone() const
 	return new PartitionLUKS( *this );
 }
 
+bool PartitionLUKS::sector_usage_known() const
+{
+	if ( busy )
+		// For an open dm-crypt mapping the usage of both the LUKS and encrypted
+		// file system must be known.
+		return Partition::sector_usage_known() && encrypted.sector_usage_known();
+	return Partition::sector_usage_known();
+}
+
+// An encrypted partition is laid out, and usage figures calculated like this:
+//
+//     Partition
+//     |<---------------------------------------->| <- this PartitionLUKS object
+//     LUKS   LUKS
+//     Header Mapping
+//     |<--->||<----------------------->|           <- encrypted Partition object member
+//     1111111111111111111111111111111111uuuuuuuuuu <- this->sectors_{used,unused,unallocated}
+//            Encrypted file system
+//            |<----------------->|
+//            111111111111110000000uuuuuu           <- encrypted.sectors_{used,unused,unallocated}
+//            ^                         ^
+//            |                         `------------- encrypted.sector_end
+//            `--------------------------------------- encrypted.sector_start (== size of LUKS header)
+//     1111111111111111111110000000uuuuuuuuuuuuuuuu <- Overall usage figures as used in the following
+//                                                     usage related methods.
+// Legend:
+// 1 - used sectors
+// 0 - unused sectors
+// u - unallocated sectors
+//
+// Calculations:
+//     total_used        = LUKS Header size + Encrypted file system used
+//                       = encrypted.sector_start + encrypted.sectors_used
+//     total_unallocated = LUKS unallocated + Encrypted file system unallocated
+//                       = this->sectors_unallocated + encrypted_unallocated
+//     total_unused      = LUKS unused + Encrypted file system unused
+//                       = 0 + encrypted.sectors_unused
+//
+//     By definition LUKS unused is 0 (See luks::set_used_sectors()).
+
+// Return estimated minimum size to which the partition can be resized.
+// See Partition::estimated_min_size() for unallocated threshold reasoning.
+Sector PartitionLUKS::estimated_min_size() const
+{
+	if ( busy )
+	{
+		// For an open dm-crypt mapping work with above described totals.
+		if ( sectors_used >= 0 && encrypted.sectors_used >= 0 )
+		{
+			Sector total_used        = encrypted.sector_start + encrypted.sectors_used;
+			Sector total_unallocated = sectors_unallocated + encrypted.sectors_unallocated;
+			return total_used + std::min( total_unallocated, significant_threshold );
+		}
+		return -1;
+	}
+	return Partition::estimated_min_size();
+}
+
+// Return user displayable used sectors.
+// See Partition::get_sectors_used() for unallocated threshold reasoning.
+Sector PartitionLUKS::get_sectors_used() const
+{
+	if ( busy )
+	{
+		// For an open dm-crypt mapping work with above described totals.
+		if ( sectors_used >= 0 && encrypted.sectors_used >= 0 )
+		{
+			Sector total_used        = encrypted.sector_start + encrypted.sectors_used;
+			Sector total_unallocated = sectors_unallocated + encrypted.sectors_unallocated;
+			if ( total_unallocated < significant_threshold )
+				return total_used + total_unallocated;
+			else
+				return total_used;
+		}
+		return -1;
+	}
+	return Partition::get_sectors_used();
+}
+
+// Return user displayable unused sectors.
+// See above described totals.
+Sector PartitionLUKS::get_sectors_unused() const
+{
+	if ( busy )
+		return encrypted.get_sectors_unused();
+	return Partition::get_sectors_unused();
+}
+
+// Return user displayable unallocated sectors.
+// See Partition::get_sectors_unallocated() for unallocated threshold reasoning.
+Sector PartitionLUKS::get_sectors_unallocated() const
+{
+	if ( busy )
+	{
+		// For an open dm-crypt mapping work with above described totals.
+		Sector total_unallocated = sectors_unallocated + encrypted.sectors_unallocated;
+		if ( total_unallocated < significant_threshold )
+			return 0;
+		else
+			return total_unallocated;
+	}
+	return Partition::get_sectors_unallocated();
+}
+
 // Return the label of the encrypted file system within, or "" if no open mapping.
 Glib::ustring PartitionLUKS::get_filesystem_label() const
 {