org.apache.hadoop.fs
Class HardLink

java.lang.Object
  org.apache.hadoop.fs.HardLink

public class HardLink
extends Object

Class for creating hardlinks. Supports Unix/Linux, WinXP/2003/Vista via Cygwin, and Mac OS X. The HardLink class was formerly a static inner class of FSUtil, and the methods provided were blatantly non-thread-safe. To enable volume-parallel Update snapshots, we now provide static threadsafe methods that allocate new buffer string arrays upon each call. We also provide an API to hardlink all files in a directory with a single command, which is up to 128 times more efficient - and minimizes the impact of the extra buffer creations.

Nested Class Summary

static class	HardLink.LinkStats HardLink statistics counters and methods.
static class	HardLink.OSType

Field Summary

HardLink.LinkStats	linkStats
static HardLink.OSType	osType

Constructor Summary

HardLink()

Method Summary

static void	createHardLink(File file, File linkName) Creates a hardlink
static void	createHardLinkMult(File parentDir, String[] fileBaseNames, File linkDir) Creates hardlinks from multiple existing files within one parent directory, into one target directory.
protected static int	createHardLinkMult(File parentDir, String[] fileBaseNames, File linkDir, int maxLength)
static int	getLinkCount(File fileName) Retrieves the number of links to the specified file.
protected static int	getLinkMultArgLength(File fileDir, String[] fileBaseNames, File linkDir) Calculate the nominal length of all contributors to the total commandstring length, including fixed overhead of the OS-dependent command.
protected static int	getMaxAllowedCmdArgLength() Return this private value for use by unit tests.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

osType

public static HardLink.OSType osType

linkStats

public final HardLink.LinkStats linkStats

Constructor Detail

HardLink

public HardLink()

Method Detail

getLinkMultArgLength

protected static int getLinkMultArgLength(File fileDir,
                                          String[] fileBaseNames,
                                          File linkDir)
                                   throws IOException

Calculate the nominal length of all contributors to the total commandstring length, including fixed overhead of the OS-dependent command. It's protected rather than private, to assist unit testing, but real clients are not expected to need it -- see the way createHardLinkMult() uses it internally so the user doesn't need to worry about it.

Parameters:

fileDir - - source directory, parent of fileBaseNames

fileBaseNames - - array of path-less file names, relative to the source directory

linkDir - - target directory where the hardlinks will be put

Returns:

- total data length (must not exceed maxAllowedCmdArgLength)

Throws:

IOException

getMaxAllowedCmdArgLength

protected static int getMaxAllowedCmdArgLength()

Return this private value for use by unit tests. Shell commands are not allowed to have a total string length exceeding this size.

createHardLink

public static void createHardLink(File file,
                                  File linkName)
                           throws IOException

Creates a hardlink

Parameters:

file - - existing source file

linkName - - desired target link file

Throws:

IOException

createHardLinkMult

public static void createHardLinkMult(File parentDir,
                                      String[] fileBaseNames,
                                      File linkDir)
                               throws IOException

Creates hardlinks from multiple existing files within one parent directory, into one target directory.

Parameters:

parentDir - - directory containing source files

fileBaseNames - - list of path-less file names, as returned by parentDir.list()

linkDir - - where the hardlinks should be put. It must already exist. If the list of files is too long (overflows maxAllowedCmdArgLength), we will automatically split it into multiple invocations of the underlying method.

Throws:

IOException

createHardLinkMult

protected static int createHardLinkMult(File parentDir,
                                        String[] fileBaseNames,
                                        File linkDir,
                                        int maxLength)
                                 throws IOException

Throws:

IOException

getLinkCount

public static int getLinkCount(File fileName)
                        throws IOException

Retrieves the number of links to the specified file.

Throws:

IOException