org.eclipse.jgit/src/org/eclipse/jgit/util/FS_POSIX.java - jgit - Git at Google

 /*
  * Copyright (C) 2010, Robin Rosenberg
  * and other copyright owners as documented in the project's IP log.
  *
  * This program and the accompanying materials are made available
  * under the terms of the Eclipse Distribution License v1.0 which
  * accompanies this distribution, is reproduced below, and is
  * available at http://www.eclipse.org/org/documents/edl-v10.php
  *
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or
  * without modification, are permitted provided that the following
  * conditions are met:
  *
  * - Redistributions of source code must retain the above copyright
  *   notice, this list of conditions and the following disclaimer.
  *
  * - Redistributions in binary form must reproduce the above
  *   copyright notice, this list of conditions and the following
  *   disclaimer in the documentation and/or other materials provided
  *   with the distribution.
  *
  * - Neither the name of the Eclipse Foundation, Inc. nor the
  *   names of its contributors may be used to endorse or promote
  *   products derived from this software without specific prior
  *   written permission.
  *
  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
  * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
  * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
  * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
  * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 package org.eclipse.jgit.util;

 import java.io.BufferedReader;
 import java.io.File;
 import java.io.IOException;
 import java.io.InputStreamReader;
 import java.io.PrintStream;
 import java.nio.charset.Charset;
 import java.nio.file.FileStore;
 import java.nio.file.FileSystemException;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.nio.file.attribute.PosixFilePermission;
 import java.text.MessageFormat;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
 import java.util.Set;
 import java.util.UUID;
 import java.util.concurrent.ConcurrentHashMap;

 import org.eclipse.jgit.annotations.Nullable;
 import org.eclipse.jgit.api.errors.JGitInternalException;
 import org.eclipse.jgit.errors.CommandFailedException;
 import org.eclipse.jgit.errors.ConfigInvalidException;
 import org.eclipse.jgit.internal.JGitText;
 import org.eclipse.jgit.lib.ConfigConstants;
 import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.storage.file.FileBasedConfig;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;

 /**
  * Base FS for POSIX based systems
  *
  * @since 3.0
  */
 public class FS_POSIX extends FS {
 	private final static Logger LOG = LoggerFactory.getLogger(FS_POSIX.class);

 	private static final int DEFAULT_UMASK = 0022;
 	private volatile int umask = -1;

 	private static final Map<FileStore, Boolean> CAN_HARD_LINK = new ConcurrentHashMap<>();

 	private volatile AtomicFileCreation supportsAtomicCreateNewFile = AtomicFileCreation.UNDEFINED;

 	private enum AtomicFileCreation {
 		SUPPORTED, NOT_SUPPORTED, UNDEFINED
 	}

 	/**
 	 * Default constructor.
 	 */
 	protected FS_POSIX() {
 	}

 	/**
 	 * Constructor
 	 *
 	 * @param src
 	 *            FS to copy some settings from
 	 */
 	protected FS_POSIX(FS src) {
 		super(src);
 		if (src instanceof FS_POSIX) {
 			umask = ((FS_POSIX) src).umask;
 		}
 	}

 	private void determineAtomicFileCreationSupport() {
 		// @TODO: enhance SystemReader to support this without copying code
 		AtomicFileCreation ret = getAtomicFileCreationSupportOption(
 				SystemReader.getInstance().openUserConfig(null, this));
 		if (ret == AtomicFileCreation.UNDEFINED
 				&& StringUtils.isEmptyOrNull(SystemReader.getInstance()
 						.getenv(Constants.GIT_CONFIG_NOSYSTEM_KEY))) {
 			ret = getAtomicFileCreationSupportOption(
 					SystemReader.getInstance().openSystemConfig(null, this));
 		}
 		supportsAtomicCreateNewFile = ret;
 	}

 	private AtomicFileCreation getAtomicFileCreationSupportOption(
 			FileBasedConfig config) {
 		try {
 			config.load();
 			String value = config.getString(ConfigConstants.CONFIG_CORE_SECTION,
 					null,
 					ConfigConstants.CONFIG_KEY_SUPPORTSATOMICFILECREATION);
 			if (value == null) {
 				return AtomicFileCreation.UNDEFINED;
 			}
 			return StringUtils.toBoolean(value)
 					? AtomicFileCreation.SUPPORTED
 					: AtomicFileCreation.NOT_SUPPORTED;
 		} catch (IOException | ConfigInvalidException e) {
 			return AtomicFileCreation.SUPPORTED;
 		}
 	}

 	/** {@inheritDoc} */
 	@Override
 	public FS newInstance() {
 		return new FS_POSIX(this);
 	}

 	/**
 	 * Set the umask, overriding any value observed from the shell.
 	 *
 	 * @param umask
 	 *            mask to apply when creating files.
 	 * @since 4.0
 	 */
 	public void setUmask(int umask) {
 		this.umask = umask;
 	}

 	private int umask() {
 		int u = umask;
 		if (u == -1) {
 			u = readUmask();
 			umask = u;
 		}
 		return u;
 	}

 	/** @return mask returned from running {@code umask} command in shell. */
 	private static int readUmask() {
 		try {
 			Process p = Runtime.getRuntime().exec(
 					new String[] { "sh", "-c", "umask" }, //$NON-NLS-1$ //$NON-NLS-2$ //$NON-NLS-3$
 					null, null);
 			try (BufferedReader lineRead = new BufferedReader(
 					new InputStreamReader(p.getInputStream(), Charset
 							.defaultCharset().name()))) {
 				if (p.waitFor() == 0) {
 					String s = lineRead.readLine();
 					if (s != null && s.matches("0?\\d{3}")) { //$NON-NLS-1$
 						return Integer.parseInt(s, 8);
 					}
 				}
 				return DEFAULT_UMASK;
 			}
 		} catch (Exception e) {
 			return DEFAULT_UMASK;
 		}
 	}

 	/** {@inheritDoc} */
 	@Override
 	protected File discoverGitExe() {
 		String path = SystemReader.getInstance().getenv("PATH"); //$NON-NLS-1$
 		File gitExe = searchPath(path, "git"); //$NON-NLS-1$

 		if (gitExe == null) {
 			if (SystemReader.getInstance().isMacOS()) {
 				if (searchPath(path, "bash") != null) { //$NON-NLS-1$
 					// On MacOSX, PATH is shorter when Eclipse is launched from the
 					// Finder than from a terminal. Therefore try to launch bash as a
 					// login shell and search using that.
 					String w;
 					try {
 						w = readPipe(userHome(),
 							new String[]{"bash", "--login", "-c", "which git"}, // //$NON-NLS-1$ //$NON-NLS-2$ //$NON-NLS-3$ //$NON-NLS-4$
 							Charset.defaultCharset().name());
 					} catch (CommandFailedException e) {
 						LOG.warn(e.getMessage());
 						return null;
 					}
 					if (!StringUtils.isEmptyOrNull(w)) {
 						gitExe = new File(w);
 					}
 				}
 			}
 		}

 		return gitExe;
 	}

 	/** {@inheritDoc} */
 	@Override
 	public boolean isCaseSensitive() {
 		return !SystemReader.getInstance().isMacOS();
 	}

 	/** {@inheritDoc} */
 	@Override
 	public boolean supportsExecute() {
 		return true;
 	}

 	/** {@inheritDoc} */
 	@Override
 	public boolean canExecute(File f) {
 		return FileUtils.canExecute(f);
 	}

 	/** {@inheritDoc} */
 	@Override
 	public boolean setExecute(File f, boolean canExecute) {
 		if (!isFile(f))
 			return false;
 		if (!canExecute)
 			return f.setExecutable(false, false);

 		try {
 			Path path = FileUtils.toPath(f);
 			Set<PosixFilePermission> pset = Files.getPosixFilePermissions(path);

 			// owner (user) is always allowed to execute.
 			pset.add(PosixFilePermission.OWNER_EXECUTE);

 			int mask = umask();
 			apply(pset, mask, PosixFilePermission.GROUP_EXECUTE, 1 << 3);
 			apply(pset, mask, PosixFilePermission.OTHERS_EXECUTE, 1);
 			Files.setPosixFilePermissions(path, pset);
 			return true;
 		} catch (IOException e) {
 			// The interface doesn't allow to throw IOException
 			final boolean debug = Boolean.parseBoolean(SystemReader
 					.getInstance().getProperty("jgit.fs.debug")); //$NON-NLS-1$
 			if (debug)
 				System.err.println(e);
 			return false;
 		}
 	}

 	private static void apply(Set<PosixFilePermission> set,
 			int umask, PosixFilePermission perm, int test) {
 		if ((umask & test) == 0) {
 			// If bit is clear in umask, permission is allowed.
 			set.add(perm);
 		} else {
 			// If bit is set in umask, permission is denied.
 			set.remove(perm);
 		}
 	}

 	/** {@inheritDoc} */
 	@Override
 	public ProcessBuilder runInShell(String cmd, String[] args) {
 		List<String> argv = new ArrayList<>(4 + args.length);
 		argv.add("sh"); //$NON-NLS-1$
 		argv.add("-c"); //$NON-NLS-1$
 		argv.add(cmd + " \"$@\""); //$NON-NLS-1$
 		argv.add(cmd);
 		argv.addAll(Arrays.asList(args));
 		ProcessBuilder proc = new ProcessBuilder();
 		proc.command(argv);
 		return proc;
 	}

 	/** {@inheritDoc} */
 	@Override
 	public ProcessResult runHookIfPresent(Repository repository, String hookName,
 			String[] args, PrintStream outRedirect, PrintStream errRedirect,
 			String stdinArgs) throws JGitInternalException {
 		return internalRunHookIfPresent(repository, hookName, args, outRedirect,
 				errRedirect, stdinArgs);
 	}

 	/** {@inheritDoc} */
 	@Override
 	public boolean retryFailedLockFileCommit() {
 		return false;
 	}

 	/** {@inheritDoc} */
 	@Override
 	public boolean supportsSymlinks() {
 		return true;
 	}

 	/** {@inheritDoc} */
 	@Override
 	public void setHidden(File path, boolean hidden) throws IOException {
 		// no action on POSIX
 	}

 	/** {@inheritDoc} */
 	@Override
 	public Attributes getAttributes(File path) {
 		return FileUtils.getFileAttributesPosix(this, path);
 	}

 	/** {@inheritDoc} */
 	@Override
 	public File normalize(File file) {
 		return FileUtils.normalize(file);
 	}

 	/** {@inheritDoc} */
 	@Override
 	public String normalize(String name) {
 		return FileUtils.normalize(name);
 	}

 	/** {@inheritDoc} */
 	@Override
 	public File findHook(Repository repository, String hookName) {
 		final File gitdir = repository.getDirectory();
 		if (gitdir == null) {
 			return null;
 		}
 		final Path hookPath = gitdir.toPath().resolve(Constants.HOOKS)
 				.resolve(hookName);
 		if (Files.isExecutable(hookPath))
 			return hookPath.toFile();
 		return null;
 	}

 	/** {@inheritDoc} */
 	@Override
 	public boolean supportsAtomicCreateNewFile() {
 		if (supportsAtomicCreateNewFile == AtomicFileCreation.UNDEFINED) {
 			determineAtomicFileCreationSupport();
 		}
 		return supportsAtomicCreateNewFile == AtomicFileCreation.SUPPORTED;
 	}

 	@Override
 	@SuppressWarnings("boxing")
 	/**
 	 * {@inheritDoc}
 	 * <p>
 	 * An implementation of the File#createNewFile() semantics which works also
 	 * on NFS. If the config option
 	 * {@code core.supportsAtomicCreateNewFile = true} (which is the default)
 	 * then simply File#createNewFile() is called.
 	 *
 	 * But if {@code core.supportsAtomicCreateNewFile = false} then after
 	 * successful creation of the lock file a hard link to that lock file is
 	 * created and the attribute nlink of the lock file is checked to be 2. If
 	 * multiple clients manage to create the same lock file nlink would be
 	 * greater than 2 showing the error.
 	 *
 	 * @see "https://www.time-travellers.org/shane/papers/NFS_considered_harmful.html"
 	 *
 	 * @deprecated use {@link FS_POSIX#createNewFileAtomic(File)} instead
 	 * @since 4.5
 	 */
 	@Deprecated
 	public boolean createNewFile(File lock) throws IOException {
 		if (!lock.createNewFile()) {
 			return false;
 		}
 		if (supportsAtomicCreateNewFile()) {
 			return true;
 		}
 		Path lockPath = lock.toPath();
 		Path link = null;
 		FileStore store = null;
 		try {
 			store = Files.getFileStore(lockPath);
 		} catch (SecurityException e) {
 			return true;
 		}
 		try {
 			Boolean canLink = CAN_HARD_LINK.computeIfAbsent(store,
 					s -> Boolean.TRUE);
 			if (Boolean.FALSE.equals(canLink)) {
 				return true;
 			}
 			link = Files.createLink(
 					Paths.get(lock.getAbsolutePath() + ".lnk"), //$NON-NLS-1$
 					lockPath);
 			Integer nlink = (Integer) (Files.getAttribute(lockPath,
 					"unix:nlink")); //$NON-NLS-1$
 			if (nlink > 2) {
 				LOG.warn(MessageFormat.format(
 						JGitText.get().failedAtomicFileCreation, lockPath,
 						nlink));
 				return false;
 			} else if (nlink < 2) {
 				CAN_HARD_LINK.put(store, Boolean.FALSE);
 			}
 			return true;
 		} catch (UnsupportedOperationException | IllegalArgumentException e) {
 			CAN_HARD_LINK.put(store, Boolean.FALSE);
 			return true;
 		} finally {
 			if (link != null) {
 				Files.delete(link);
 			}
 		}
 	}

 	/**
 	 * {@inheritDoc}
 	 * <p>
 	 * An implementation of the File#createNewFile() semantics which can create
 	 * a unique file atomically also on NFS. If the config option
 	 * {@code core.supportsAtomicCreateNewFile = true} (which is the default)
 	 * then simply File#createNewFile() is called.
 	 *
 	 * But if {@code core.supportsAtomicCreateNewFile = false} then after
 	 * successful creation of the lock file a hard link to that lock file is
 	 * created and the attribute nlink of the lock file is checked to be 2. If
 	 * multiple clients manage to create the same lock file nlink would be
 	 * greater than 2 showing the error. The hard link needs to be retained
 	 * until the corresponding file is no longer needed in order to prevent that
 	 * another process can create the same file concurrently using another NFS
 	 * client which might not yet see the file due to caching.
 	 *
 	 * @see "https://www.time-travellers.org/shane/papers/NFS_considered_harmful.html"
 	 * @param file
 	 *            the unique file to be created atomically
 	 * @return LockToken this lock token must be held until the file is no
 	 *         longer needed
 	 * @throws IOException
 	 * @since 5.0
 	 */
 	@Override
 	public LockToken createNewFileAtomic(File file) throws IOException {
 		if (!file.createNewFile()) {
 			return token(false, null);
 		}
 		if (supportsAtomicCreateNewFile()) {
 			return token(true, null);
 		}
 		Path link = null;
 		Path path = file.toPath();
 		FileStore store = null;
 		try {
 			store = Files.getFileStore(path);
 		} catch (SecurityException e) {
 			return token(true, null);
 		}
 		try {
 			Boolean canLink = CAN_HARD_LINK.computeIfAbsent(store,
 					s -> Boolean.TRUE);
 			if (Boolean.FALSE.equals(canLink)) {
 				return token(true, null);
 			}
 			link = Files.createLink(Paths.get(uniqueLinkPath(file)), path);
 			Integer nlink = (Integer) (Files.getAttribute(path,
 					"unix:nlink")); //$NON-NLS-1$
 			if (nlink.intValue() > 2) {
 				LOG.warn(MessageFormat.format(
 						JGitText.get().failedAtomicFileCreation, path, nlink));
 				return token(false, link);
 			} else if (nlink.intValue() < 2) {
 				CAN_HARD_LINK.put(store, Boolean.FALSE);
 			}
 			return token(true, link);
 		} catch (UnsupportedOperationException | IllegalArgumentException
 				| FileSystemException | SecurityException e) {
 			CAN_HARD_LINK.put(store, Boolean.FALSE);
 			return token(true, link);
 		}
 	}

 	private static LockToken token(boolean created, @Nullable Path p) {
 		return ((p != null) && Files.exists(p))
 				? new LockToken(created, Optional.of(p))
 				: new LockToken(created, Optional.empty());
 	}

 	private static String uniqueLinkPath(File file) {
 		UUID id = UUID.randomUUID();
 		return file.getAbsolutePath() + "." //$NON-NLS-1$
 				+ Long.toHexString(id.getMostSignificantBits())
 				+ Long.toHexString(id.getLeastSignificantBits());
 	}
 }
	/*
	* Copyright (C) 2010, Robin Rosenberg
	* and other copyright owners as documented in the project's IP log.
	*
	* This program and the accompanying materials are made available
	* under the terms of the Eclipse Distribution License v1.0 which
	* accompanies this distribution, is reproduced below, and is
	* available at http://www.eclipse.org/org/documents/edl-v10.php
	*
	* All rights reserved.
	*
	* Redistribution and use in source and binary forms, with or
	* without modification, are permitted provided that the following
	* conditions are met:
	*
	* - Redistributions of source code must retain the above copyright
	* notice, this list of conditions and the following disclaimer.
	*
	* - Redistributions in binary form must reproduce the above
	* copyright notice, this list of conditions and the following
	* disclaimer in the documentation and/or other materials provided
	* with the distribution.
	*
	* - Neither the name of the Eclipse Foundation, Inc. nor the
	* names of its contributors may be used to endorse or promote
	* products derived from this software without specific prior
	* written permission.
	*
	* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
	* CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
	* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
	* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
	* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
	* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
	* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
	* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
	* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
	* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
	* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
	* ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
	*/
	package org.eclipse.jgit.util;

	import java.io.BufferedReader;
	import java.io.File;
	import java.io.IOException;
	import java.io.InputStreamReader;
	import java.io.PrintStream;
	import java.nio.charset.Charset;
	import java.nio.file.FileStore;
	import java.nio.file.FileSystemException;
	import java.nio.file.Files;
	import java.nio.file.Path;
	import java.nio.file.Paths;
	import java.nio.file.attribute.PosixFilePermission;
	import java.text.MessageFormat;
	import java.util.ArrayList;
	import java.util.Arrays;
	import java.util.List;
	import java.util.Map;
	import java.util.Optional;
	import java.util.Set;
	import java.util.UUID;
	import java.util.concurrent.ConcurrentHashMap;

	import org.eclipse.jgit.annotations.Nullable;
	import org.eclipse.jgit.api.errors.JGitInternalException;
	import org.eclipse.jgit.errors.CommandFailedException;
	import org.eclipse.jgit.errors.ConfigInvalidException;
	import org.eclipse.jgit.internal.JGitText;
	import org.eclipse.jgit.lib.ConfigConstants;
	import org.eclipse.jgit.lib.Constants;
	import org.eclipse.jgit.lib.Repository;
	import org.eclipse.jgit.storage.file.FileBasedConfig;
	import org.slf4j.Logger;
	import org.slf4j.LoggerFactory;

	/**
	* Base FS for POSIX based systems
	*
	* @since 3.0
	*/
	public class FS_POSIX extends FS {
	private final static Logger LOG = LoggerFactory.getLogger(FS_POSIX.class);

	private static final int DEFAULT_UMASK = 0022;
	private volatile int umask = -1;

	private static final Map<FileStore, Boolean> CAN_HARD_LINK = new ConcurrentHashMap<>();

	private volatile AtomicFileCreation supportsAtomicCreateNewFile = AtomicFileCreation.UNDEFINED;

	private enum AtomicFileCreation {
	SUPPORTED, NOT_SUPPORTED, UNDEFINED
	}

	/**
	* Default constructor.
	*/
	protected FS_POSIX() {
	}

	/**
	* Constructor
	*
	* @param src
	* FS to copy some settings from
	*/
	protected FS_POSIX(FS src) {
	super(src);
	if (src instanceof FS_POSIX) {
	umask = ((FS_POSIX) src).umask;
	}
	}

	private void determineAtomicFileCreationSupport() {
	// @TODO: enhance SystemReader to support this without copying code
	AtomicFileCreation ret = getAtomicFileCreationSupportOption(
	SystemReader.getInstance().openUserConfig(null, this));
	if (ret == AtomicFileCreation.UNDEFINED
	&& StringUtils.isEmptyOrNull(SystemReader.getInstance()
	.getenv(Constants.GIT_CONFIG_NOSYSTEM_KEY))) {
	ret = getAtomicFileCreationSupportOption(
	SystemReader.getInstance().openSystemConfig(null, this));
	}
	supportsAtomicCreateNewFile = ret;
	}

	private AtomicFileCreation getAtomicFileCreationSupportOption(
	FileBasedConfig config) {
	try {
	config.load();
	String value = config.getString(ConfigConstants.CONFIG_CORE_SECTION,
	null,
	ConfigConstants.CONFIG_KEY_SUPPORTSATOMICFILECREATION);
	if (value == null) {
	return AtomicFileCreation.UNDEFINED;
	}
	return StringUtils.toBoolean(value)
	? AtomicFileCreation.SUPPORTED
	: AtomicFileCreation.NOT_SUPPORTED;
	} catch (IOException \| ConfigInvalidException e) {
	return AtomicFileCreation.SUPPORTED;
	}
	}

	/** {@inheritDoc} */
	@Override
	public FS newInstance() {
	return new FS_POSIX(this);
	}

	/**
	* Set the umask, overriding any value observed from the shell.
	*
	* @param umask
	* mask to apply when creating files.
	* @since 4.0
	*/
	public void setUmask(int umask) {
	this.umask = umask;
	}

	private int umask() {
	int u = umask;
	if (u == -1) {
	u = readUmask();
	umask = u;
	}
	return u;
	}

	/** @return mask returned from running {@code umask} command in shell. */
	private static int readUmask() {
	try {
	Process p = Runtime.getRuntime().exec(
	new String[] { "sh", "-c", "umask" }, //$NON-NLS-1$ //$NON-NLS-2$ //$NON-NLS-3$
	null, null);
	try (BufferedReader lineRead = new BufferedReader(
	new InputStreamReader(p.getInputStream(), Charset
	.defaultCharset().name()))) {
	if (p.waitFor() == 0) {
	String s = lineRead.readLine();
	if (s != null && s.matches("0?\\d{3}")) { //$NON-NLS-1$
	return Integer.parseInt(s, 8);
	}
	}
	return DEFAULT_UMASK;
	}
	} catch (Exception e) {
	return DEFAULT_UMASK;
	}
	}

	/** {@inheritDoc} */
	@Override
	protected File discoverGitExe() {
	String path = SystemReader.getInstance().getenv("PATH"); //$NON-NLS-1$
	File gitExe = searchPath(path, "git"); //$NON-NLS-1$

	if (gitExe == null) {
	if (SystemReader.getInstance().isMacOS()) {
	if (searchPath(path, "bash") != null) { //$NON-NLS-1$
	// On MacOSX, PATH is shorter when Eclipse is launched from the
	// Finder than from a terminal. Therefore try to launch bash as a
	// login shell and search using that.
	String w;
	try {
	w = readPipe(userHome(),
	new String[]{"bash", "--login", "-c", "which git"}, // //$NON-NLS-1$ //$NON-NLS-2$ //$NON-NLS-3$ //$NON-NLS-4$
	Charset.defaultCharset().name());
	} catch (CommandFailedException e) {
	LOG.warn(e.getMessage());
	return null;
	}
	if (!StringUtils.isEmptyOrNull(w)) {
	gitExe = new File(w);
	}
	}
	}
	}

	return gitExe;
	}

	/** {@inheritDoc} */
	@Override
	public boolean isCaseSensitive() {
	return !SystemReader.getInstance().isMacOS();
	}

	/** {@inheritDoc} */
	@Override
	public boolean supportsExecute() {
	return true;
	}

	/** {@inheritDoc} */
	@Override
	public boolean canExecute(File f) {
	return FileUtils.canExecute(f);
	}

	/** {@inheritDoc} */
	@Override
	public boolean setExecute(File f, boolean canExecute) {
	if (!isFile(f))
	return false;
	if (!canExecute)
	return f.setExecutable(false, false);

	try {
	Path path = FileUtils.toPath(f);
	Set<PosixFilePermission> pset = Files.getPosixFilePermissions(path);

	// owner (user) is always allowed to execute.
	pset.add(PosixFilePermission.OWNER_EXECUTE);

	int mask = umask();
	apply(pset, mask, PosixFilePermission.GROUP_EXECUTE, 1 << 3);
	apply(pset, mask, PosixFilePermission.OTHERS_EXECUTE, 1);
	Files.setPosixFilePermissions(path, pset);
	return true;
	} catch (IOException e) {
	// The interface doesn't allow to throw IOException
	final boolean debug = Boolean.parseBoolean(SystemReader
	.getInstance().getProperty("jgit.fs.debug")); //$NON-NLS-1$
	if (debug)
	System.err.println(e);
	return false;
	}
	}

	private static void apply(Set<PosixFilePermission> set,
	int umask, PosixFilePermission perm, int test) {
	if ((umask & test) == 0) {
	// If bit is clear in umask, permission is allowed.
	set.add(perm);
	} else {
	// If bit is set in umask, permission is denied.
	set.remove(perm);
	}
	}

	/** {@inheritDoc} */
	@Override
	public ProcessBuilder runInShell(String cmd, String[] args) {
	List<String> argv = new ArrayList<>(4 + args.length);
	argv.add("sh"); //$NON-NLS-1$
	argv.add("-c"); //$NON-NLS-1$
	argv.add(cmd + " \"$@\""); //$NON-NLS-1$
	argv.add(cmd);
	argv.addAll(Arrays.asList(args));
	ProcessBuilder proc = new ProcessBuilder();
	proc.command(argv);
	return proc;
	}

	/** {@inheritDoc} */
	@Override
	public ProcessResult runHookIfPresent(Repository repository, String hookName,
	String[] args, PrintStream outRedirect, PrintStream errRedirect,
	String stdinArgs) throws JGitInternalException {
	return internalRunHookIfPresent(repository, hookName, args, outRedirect,
	errRedirect, stdinArgs);
	}

	/** {@inheritDoc} */
	@Override
	public boolean retryFailedLockFileCommit() {
	return false;
	}

	/** {@inheritDoc} */
	@Override
	public boolean supportsSymlinks() {
	return true;
	}

	/** {@inheritDoc} */
	@Override
	public void setHidden(File path, boolean hidden) throws IOException {
	// no action on POSIX
	}

	/** {@inheritDoc} */
	@Override
	public Attributes getAttributes(File path) {
	return FileUtils.getFileAttributesPosix(this, path);
	}

	/** {@inheritDoc} */
	@Override
	public File normalize(File file) {
	return FileUtils.normalize(file);
	}

	/** {@inheritDoc} */
	@Override
	public String normalize(String name) {
	return FileUtils.normalize(name);
	}

	/** {@inheritDoc} */
	@Override
	public File findHook(Repository repository, String hookName) {
	final File gitdir = repository.getDirectory();
	if (gitdir == null) {
	return null;
	}
	final Path hookPath = gitdir.toPath().resolve(Constants.HOOKS)
	.resolve(hookName);
	if (Files.isExecutable(hookPath))
	return hookPath.toFile();
	return null;
	}

	/** {@inheritDoc} */
	@Override
	public boolean supportsAtomicCreateNewFile() {
	if (supportsAtomicCreateNewFile == AtomicFileCreation.UNDEFINED) {
	determineAtomicFileCreationSupport();
	}
	return supportsAtomicCreateNewFile == AtomicFileCreation.SUPPORTED;
	}

	@Override
	@SuppressWarnings("boxing")
	/**
	* {@inheritDoc}
	* <p>
	* An implementation of the File#createNewFile() semantics which works also
	* on NFS. If the config option
	* {@code core.supportsAtomicCreateNewFile = true} (which is the default)
	* then simply File#createNewFile() is called.
	*
	* But if {@code core.supportsAtomicCreateNewFile = false} then after
	* successful creation of the lock file a hard link to that lock file is
	* created and the attribute nlink of the lock file is checked to be 2. If
	* multiple clients manage to create the same lock file nlink would be
	* greater than 2 showing the error.
	*
	* @see "https://www.time-travellers.org/shane/papers/NFS_considered_harmful.html"
	*
	* @deprecated use {@link FS_POSIX#createNewFileAtomic(File)} instead
	* @since 4.5
	*/
	@Deprecated
	public boolean createNewFile(File lock) throws IOException {
	if (!lock.createNewFile()) {
	return false;
	}
	if (supportsAtomicCreateNewFile()) {
	return true;
	}
	Path lockPath = lock.toPath();
	Path link = null;
	FileStore store = null;
	try {
	store = Files.getFileStore(lockPath);
	} catch (SecurityException e) {
	return true;
	}
	try {
	Boolean canLink = CAN_HARD_LINK.computeIfAbsent(store,
	s -> Boolean.TRUE);
	if (Boolean.FALSE.equals(canLink)) {
	return true;
	}
	link = Files.createLink(
	Paths.get(lock.getAbsolutePath() + ".lnk"), //$NON-NLS-1$
	lockPath);
	Integer nlink = (Integer) (Files.getAttribute(lockPath,
	"unix:nlink")); //$NON-NLS-1$
	if (nlink > 2) {
	LOG.warn(MessageFormat.format(
	JGitText.get().failedAtomicFileCreation, lockPath,
	nlink));
	return false;
	} else if (nlink < 2) {
	CAN_HARD_LINK.put(store, Boolean.FALSE);
	}
	return true;
	} catch (UnsupportedOperationException \| IllegalArgumentException e) {
	CAN_HARD_LINK.put(store, Boolean.FALSE);
	return true;
	} finally {
	if (link != null) {
	Files.delete(link);
	}
	}
	}

	/**
	* {@inheritDoc}
	* <p>
	* An implementation of the File#createNewFile() semantics which can create
	* a unique file atomically also on NFS. If the config option
	* {@code core.supportsAtomicCreateNewFile = true} (which is the default)
	* then simply File#createNewFile() is called.
	*
	* But if {@code core.supportsAtomicCreateNewFile = false} then after
	* successful creation of the lock file a hard link to that lock file is
	* created and the attribute nlink of the lock file is checked to be 2. If
	* multiple clients manage to create the same lock file nlink would be
	* greater than 2 showing the error. The hard link needs to be retained
	* until the corresponding file is no longer needed in order to prevent that
	* another process can create the same file concurrently using another NFS
	* client which might not yet see the file due to caching.
	*
	* @see "https://www.time-travellers.org/shane/papers/NFS_considered_harmful.html"
	* @param file
	* the unique file to be created atomically
	* @return LockToken this lock token must be held until the file is no
	* longer needed
	* @throws IOException
	* @since 5.0
	*/
	@Override
	public LockToken createNewFileAtomic(File file) throws IOException {
	if (!file.createNewFile()) {
	return token(false, null);
	}
	if (supportsAtomicCreateNewFile()) {
	return token(true, null);
	}
	Path link = null;
	Path path = file.toPath();
	FileStore store = null;
	try {
	store = Files.getFileStore(path);
	} catch (SecurityException e) {
	return token(true, null);
	}
	try {
	Boolean canLink = CAN_HARD_LINK.computeIfAbsent(store,
	s -> Boolean.TRUE);
	if (Boolean.FALSE.equals(canLink)) {
	return token(true, null);
	}
	link = Files.createLink(Paths.get(uniqueLinkPath(file)), path);
	Integer nlink = (Integer) (Files.getAttribute(path,
	"unix:nlink")); //$NON-NLS-1$
	if (nlink.intValue() > 2) {
	LOG.warn(MessageFormat.format(
	JGitText.get().failedAtomicFileCreation, path, nlink));
	return token(false, link);
	} else if (nlink.intValue() < 2) {
	CAN_HARD_LINK.put(store, Boolean.FALSE);
	}
	return token(true, link);
	} catch (UnsupportedOperationException \| IllegalArgumentException
	\| FileSystemException \| SecurityException e) {
	CAN_HARD_LINK.put(store, Boolean.FALSE);
	return token(true, link);
	}
	}

	private static LockToken token(boolean created, @Nullable Path p) {
	return ((p != null) && Files.exists(p))
	? new LockToken(created, Optional.of(p))
	: new LockToken(created, Optional.empty());
	}

	private static String uniqueLinkPath(File file) {
	UUID id = UUID.randomUUID();
	return file.getAbsolutePath() + "." //$NON-NLS-1$
	+ Long.toHexString(id.getMostSignificantBits())
	+ Long.toHexString(id.getLeastSignificantBits());
	}
	}