/// <summary>
/// Reads the file descriptor sector for a given file and verified that all sectors in the file segment list (and the file descriptor sector itself)
/// are marked as free in the passed cluster allocation map. It then marks the clusters as marked.
/// </summary>
/// <param name="map">Cluster allocation map.</param>
/// <param name="filedesc">Logical sector number of the file descriptor sector for the file.</param>
/// <param name="clustersize">Cluster size for this filesystem.</param>
/// <exception cref="FilesystemConsistencyException">Thrown if any cluster used for this file is already allocated.</exception>
private void VerifyAndUpdateAllocationMap(OS9AllocationMap map, int filedesc, int clustersize)
{
var fileinfo = OS9FileInfo.Parse(ReadSector(filedesc), null);
/* Verify that all sectors used by this file are marked as free in the cluster allocation map. */
if (map.IsAllocated(filedesc / clustersize))
{
throw new FilesystemConsistencyException(String.Format("Sector {0} is in use by multiple files", filedesc));
}
foreach (var segment in fileinfo.Segments)
{
int sector = segment.Lsn;
for (int i = 0; i < segment.Size; i++)
{
if (map.IsAllocated(sector / clustersize))
{
throw new FilesystemConsistencyException(String.Format("Sector {0} is in use by multiple files", sector));
}
sector++;
}
}
/* Mark all sectors as allocated. */
map.SetAllocated(filedesc / clustersize, true);
foreach (var segment in fileinfo.Segments)
{
int sector = segment.Lsn;
for (int i = 0; i < segment.Size; i++)
{
map.SetAllocated(sector / clustersize, true);
sector++;
}
}
}
/// <summary>
/// Checks the filesystem consistency.
/// </summary>
/// <exception cref="FilesystemConsistencyException">Thrown if the filesystem is not consistent in a manner that makes write operations unsafe.</exception>
public void Check()
{
if (IsDisposed)
{
throw new ObjectDisposedException(GetType().FullName);
}
ReadDiskHeader();
var allocmap = new OS9AllocationMap(DiskInfo.AllocationMapSize); // mirror the allocation map
allocmap.SetAllocated(IdentificationSector / DiskInfo.ClusterSize, true);
allocmap.SetAllocated(AllocationMapSector / DiskInfo.ClusterSize, true);
var dirs = new Queue <int>(); // LSN of all directories found while traversing the file structure
dirs.Enqueue(DiskInfo.RootDirectory);
VerifyAndUpdateAllocationMap(allocmap, DiskInfo.RootDirectory, DiskInfo.ClusterSize);
/* Traverse the directory hierarchy and update the cluster allocation map for all files encountered. */
while (dirs.Count > 0)
{
int lsn = dirs.Dequeue();
var files = ReadDirectory(lsn);
foreach (var file in files)
{
if (file.IsValid && !String.Equals(file.Filename, ".") && !String.Equals(file.Filename, ".."))
{
VerifyAndUpdateAllocationMap(allocmap, file.Sector, DiskInfo.ClusterSize);
var fileinfo = OS9FileInfo.Parse(ReadSector(file.Sector), file.Filename);
if (fileinfo.IsDirectory)
{
dirs.Enqueue(file.Sector);
}
}
}
}
/* Finally, verify that all clusters used by files found are actually marked as allocated in the disk cluster allocation map. */
for (int i = 0; i < AllocationMap.AllocationMapSize; i++)
{
if (allocmap.IsAllocated(i) && !AllocationMap.IsAllocated(i))
{
throw new FilesystemConsistencyException(String.Format("Cluster {0} is in use by a file but not marked as allocated", i));
}
}
}
/// <summary>
/// Reads a directory starting at a given disk sector.
/// </summary>
/// <param name="sector">First sector of the directory file.</param>
/// <returns>A list of (filename, sector) tuples for the entries in the directory.</returns>
internal List <OS9DirectoryEntry> ReadDirectory(int sector)
{
var header = OS9FileInfo.Parse(ReadSector(sector), null);
if (!header.IsDirectory)
{
throw new InvalidFileException();
}
var dir = new List <OS9DirectoryEntry>();
var raw = ReadFile(header);
int direntries = raw.Length / OS9DirectoryEntry.RawEntrySize;
for (int i = 0; i < direntries; i++)
{
dir.Add(new OS9DirectoryEntry(raw, i));
}
return(dir);
}
/// <summary>
/// Returns meta-information for a named file.
/// </summary>
/// <param name="filename">Name of file</param>
/// <returns>File meta-information object.</returns>
public IFileInfo GetFileInfo(string filename)
{
if (IsDisposed)
{
throw new ObjectDisposedException(GetType().FullName);
}
if (filename == null)
{
throw new ArgumentNullException();
}
int sector = FindPath(filename);
if (sector == -1)
{
throw new FileNotFoundException(filename);
}
var raw = ReadSector(sector);
return(OS9FileInfo.Parse(raw, filename));
}
