src/main/java/com/google/devtools/build/lib/unix/UnixFileSystem.java - bazel - Git at Google

 // Copyright 2014 The Bazel Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //    http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
 package com.google.devtools.build.lib.unix;

 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Preconditions;
 import com.google.common.collect.Lists;
 import com.google.devtools.build.lib.concurrent.ThreadSafety.ThreadSafe;
 import com.google.devtools.build.lib.profiler.Profiler;
 import com.google.devtools.build.lib.profiler.ProfilerTask;
 import com.google.devtools.build.lib.unix.NativePosixFiles.Dirents;
 import com.google.devtools.build.lib.unix.NativePosixFiles.ReadTypes;
 import com.google.devtools.build.lib.vfs.AbstractFileSystemWithCustomStat;
 import com.google.devtools.build.lib.vfs.DigestHashFunction;
 import com.google.devtools.build.lib.vfs.DigestHashFunction.DefaultHashFunctionNotSetException;
 import com.google.devtools.build.lib.vfs.Dirent;
 import com.google.devtools.build.lib.vfs.FileStatus;
 import com.google.devtools.build.lib.vfs.Path;
 import com.google.devtools.build.lib.vfs.PathFragment;
 import com.google.devtools.build.lib.vfs.Symlinks;
 import java.io.File;
 import java.io.FileInputStream;
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
 import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;

 /**
  * This class implements the FileSystem interface using direct calls to the UNIX filesystem.
  */
 @ThreadSafe
 public class UnixFileSystem extends AbstractFileSystemWithCustomStat {

   public UnixFileSystem() throws DefaultHashFunctionNotSetException {}

   public UnixFileSystem(DigestHashFunction hashFunction) {
     super(hashFunction);
   }

   /**
    * Eager implementation of FileStatus for file systems that have an atomic
    * stat(2) syscall. A proxy for {@link com.google.devtools.build.lib.unix.FileStatus}.
    * Note that isFile and getLastModifiedTime have slightly different meanings
    * between UNIX and VFS.
    */
   @VisibleForTesting
   protected static class UnixFileStatus implements FileStatus {

     private final com.google.devtools.build.lib.unix.FileStatus status;

     UnixFileStatus(com.google.devtools.build.lib.unix.FileStatus status) {
       this.status = status;
     }

     @Override
     public boolean isFile() { return !isDirectory() && !isSymbolicLink(); }

     @Override
     public boolean isDirectory() { return status.isDirectory(); }

     @Override
     public boolean isSymbolicLink() { return status.isSymbolicLink(); }

     @Override
     public boolean isSpecialFile() { return isFile() && !status.isRegularFile(); }

     @Override
     public long getSize() { return status.getSize(); }

     @Override
     public long getLastModifiedTime() {
       return (status.getLastModifiedTime() * 1000)
           + (status.getFractionalLastModifiedTime() / 1000000);
     }

     @Override
     public long getLastChangeTime() {
       return (status.getLastChangeTime() * 1000)
           + (status.getFractionalLastChangeTime() / 1000000);
     }

     @Override
     public long getNodeId() {
       // Note that we may want to include more information in this id number going forward,
       // especially the device number.
       return status.getInodeNumber();
     }

     int getPermissions() { return status.getPermissions(); }

     @Override
     public String toString() { return status.toString(); }
   }

   @Override
   protected Collection<String> getDirectoryEntries(Path path) throws IOException {
     String name = path.getPathString();
     String[] entries;
     long startTime = Profiler.nanoTimeMaybe();
     try {
       entries = NativePosixFiles.readdir(name);
     } finally {
       profiler.logSimpleTask(startTime, ProfilerTask.VFS_DIR, name);
     }
     Collection<String> result = new ArrayList<>(entries.length);
     for (String entry : entries) {
       result.add(entry);
     }
     return result;
   }

   @Override
   protected PathFragment resolveOneLink(Path path) throws IOException {
     // Beware, this seemingly simple code belies the complex specification of
     // FileSystem.resolveOneLink().
     return stat(path, false).isSymbolicLink()
         ? readSymbolicLink(path)
         : null;
   }

   /**
    * Converts from {@link com.google.devtools.build.lib.unix.NativePosixFiles.Dirents.Type} to
    * {@link com.google.devtools.build.lib.vfs.Dirent.Type}.
    */
   private static Dirent.Type convertToDirentType(Dirents.Type type) {
     switch (type) {
       case FILE:
         return Dirent.Type.FILE;
       case DIRECTORY:
         return Dirent.Type.DIRECTORY;
       case SYMLINK:
         return Dirent.Type.SYMLINK;
       case UNKNOWN:
         return Dirent.Type.UNKNOWN;
       default:
         throw new IllegalArgumentException("Unknown type " + type);
     }
   }

   @Override
   protected Collection<Dirent> readdir(Path path, boolean followSymlinks) throws IOException {
     String name = path.getPathString();
     long startTime = Profiler.nanoTimeMaybe();
     try {
       Dirents unixDirents = NativePosixFiles.readdir(name,
           followSymlinks ? ReadTypes.FOLLOW : ReadTypes.NOFOLLOW);
       Preconditions.checkState(unixDirents.hasTypes());
       List<Dirent> dirents = Lists.newArrayListWithCapacity(unixDirents.size());
       for (int i = 0; i < unixDirents.size(); i++) {
         dirents.add(new Dirent(unixDirents.getName(i),
             convertToDirentType(unixDirents.getType(i))));
       }
       return dirents;
     } finally {
       profiler.logSimpleTask(startTime, ProfilerTask.VFS_DIR, name);
     }
   }

   @Override
   protected FileStatus stat(Path path, boolean followSymlinks) throws IOException {
     return statInternal(path, followSymlinks);
   }

   @VisibleForTesting
   protected UnixFileStatus statInternal(Path path, boolean followSymlinks) throws IOException {
     String name = path.getPathString();
     long startTime = Profiler.nanoTimeMaybe();
     try {
       return new UnixFileStatus(followSymlinks
                                       ? NativePosixFiles.stat(name)
                                       : NativePosixFiles.lstat(name));
     } finally {
       profiler.logSimpleTask(startTime, ProfilerTask.VFS_STAT, name);
     }
   }

   // Like stat(), but returns null instead of throwing.
   // This is a performance optimization in the case where clients
   // catch and don't re-throw.
   @Override
   protected FileStatus statNullable(Path path, boolean followSymlinks) {
     String name = path.getPathString();
     long startTime = Profiler.nanoTimeMaybe();
     try {
       ErrnoFileStatus stat = followSymlinks
           ? NativePosixFiles.errnoStat(name)
           : NativePosixFiles.errnoLstat(name);
       return stat.hasError() ? null : new UnixFileStatus(stat);
     } finally {
       profiler.logSimpleTask(startTime, ProfilerTask.VFS_STAT, name);
     }
   }

   @Override
   protected boolean exists(Path path, boolean followSymlinks) {
     return statNullable(path, followSymlinks) != null;
   }

   /**
    * Return true iff the {@code stat} of {@code path} resulted in an {@code ENOENT}
    * or {@code ENOTDIR} error.
    */
   @Override
   protected FileStatus statIfFound(Path path, boolean followSymlinks) throws IOException {
     String name = path.getPathString();
     long startTime = Profiler.nanoTimeMaybe();
     try {
       ErrnoFileStatus stat = followSymlinks
           ? NativePosixFiles.errnoStat(name)
           : NativePosixFiles.errnoLstat(name);
       if (!stat.hasError()) {
         return new UnixFileStatus(stat);
       }
       int errno = stat.getErrno();
       if (errno == ErrnoFileStatus.ENOENT || errno == ErrnoFileStatus.ENOTDIR) {
         return null;
       }
       // This should not return -- we are calling stat here just to throw the proper exception.
       // However, since there may be transient IO errors, we cannot guarantee that an exception will
       // be thrown.
       // TODO(bazel-team): Extract the exception-construction code and make it visible separately in
       // FilesystemUtils to avoid having to do a duplicate stat call.
       return stat(path, followSymlinks);
     } finally {
       profiler.logSimpleTask(startTime, ProfilerTask.VFS_STAT, name);
     }
   }

   @Override
   protected boolean isReadable(Path path) throws IOException {
     return (statInternal(path, true).getPermissions() & 0400) != 0;
   }

   @Override
   protected boolean isWritable(Path path) throws IOException {
     return (statInternal(path, true).getPermissions() & 0200) != 0;
   }

   @Override
   protected boolean isExecutable(Path path) throws IOException {
     return (statInternal(path, true).getPermissions() & 0100) != 0;
   }

   /**
    * Adds or remove the bits specified in "permissionBits" to the permission
    * mask of the file specified by {@code path}. If the argument {@code add} is
    * true, the specified permissions are added, otherwise they are removed.
    *
    * @throws IOException if there was an error writing the file's metadata
    */
   private void modifyPermissionBits(Path path, int permissionBits, boolean add)
     throws IOException {
     int oldMode = statInternal(path, true).getPermissions();
     int newMode = add ? (oldMode | permissionBits) : (oldMode & ~permissionBits);
     NativePosixFiles.chmod(path.toString(), newMode);
   }

   @Override
   protected void setReadable(Path path, boolean readable) throws IOException {
     modifyPermissionBits(path, 0400, readable);
   }

   @Override
   public void setWritable(Path path, boolean writable) throws IOException {
     modifyPermissionBits(path, 0200, writable);
   }

   @Override
   protected void setExecutable(Path path, boolean executable) throws IOException {
     modifyPermissionBits(path, 0111, executable);
   }

   @Override
   protected void chmod(Path path, int mode) throws IOException {
     NativePosixFiles.chmod(path.toString(), mode);
   }

   @Override
   public boolean supportsModifications(Path path) {
     return true;
   }

   @Override
   public boolean supportsSymbolicLinksNatively(Path path) {
     return true;
   }

   @Override
   public boolean supportsHardLinksNatively(Path path) {
     return true;
   }

   @Override
   public boolean isFilePathCaseSensitive() {
     return true;
   }

   @Override
   public boolean createDirectory(Path path) throws IOException {
     // Note: UNIX mkdir(2), FilesystemUtils.mkdir() and createDirectory all
     // have different ways of representing failure!
     if (NativePosixFiles.mkdir(path.toString(), 0777)) {
       return true; // successfully created
     }

     // false => EEXIST: something is already in the way (file/dir/symlink)
     if (isDirectory(path, false)) {
       return false; // directory already existed
     } else {
       throw new IOException(path + " (File exists)");
     }
   }

   @Override
   public void createDirectoryAndParents(Path path) throws IOException {
     NativePosixFiles.mkdirs(path.toString(), 0777);
   }

   @Override
   protected void createSymbolicLink(Path linkPath, PathFragment targetFragment)
       throws IOException {
     NativePosixFiles.symlink(targetFragment.getSafePathString(), linkPath.toString());
   }

   @Override
   protected PathFragment readSymbolicLink(Path path) throws IOException {
     // Note that the default implementation of readSymbolicLinkUnchecked calls this method and thus
     // is optimal since we only make one system call in here.
     String name = path.toString();
     long startTime = Profiler.nanoTimeMaybe();
     try {
       return PathFragment.create(NativePosixFiles.readlink(name));
     } catch (IOException e) {
       // EINVAL => not a symbolic link.  Anything else is a real error.
       throw e.getMessage().endsWith("(Invalid argument)") ? new NotASymlinkException(path) : e;
     } finally {
       profiler.logSimpleTask(startTime, ProfilerTask.VFS_READLINK, name);
     }
   }

   @Override
   public void renameTo(Path sourcePath, Path targetPath) throws IOException {
     NativePosixFiles.rename(sourcePath.toString(), targetPath.toString());
   }

   @Override
   protected long getFileSize(Path path, boolean followSymlinks) throws IOException {
     return stat(path, followSymlinks).getSize();
   }

   @Override
   public boolean delete(Path path) throws IOException {
     String name = path.toString();
     long startTime = Profiler.nanoTimeMaybe();
     try {
       return NativePosixFiles.remove(name);
     } finally {
       profiler.logSimpleTask(startTime, ProfilerTask.VFS_DELETE, name);
     }
   }

   @Override
   protected long getLastModifiedTime(Path path, boolean followSymlinks) throws IOException {
     return stat(path, followSymlinks).getLastModifiedTime();
   }

   @Override
   public void setLastModifiedTime(Path path, long newTime) throws IOException {
     if (newTime == -1L) { // "now"
       NativePosixFiles.utime(path.toString(), true, 0);
     } else {
       // newTime > MAX_INT => -ve unixTime
       int unixTime = (int) (newTime / 1000);
       NativePosixFiles.utime(path.toString(), false, unixTime);
     }
   }

   @Override
   public byte[] getxattr(Path path, String name, boolean followSymlinks) throws IOException {
     String pathName = path.toString();
     long startTime = Profiler.nanoTimeMaybe();
     try {
       return followSymlinks
           ? NativePosixFiles.getxattr(pathName, name)
           : NativePosixFiles.lgetxattr(pathName, name);
     } catch (UnsupportedOperationException e) {
       // getxattr() syscall is not supported by the underlying filesystem (it returned ENOTSUP).
       // Per method contract, treat this as ENODATA.
       return null;
     } finally {
       profiler.logSimpleTask(startTime, ProfilerTask.VFS_XATTR, pathName);
     }
   }

   @Override
   protected byte[] getDigest(Path path) throws IOException {
     String name = path.toString();
     long startTime = Profiler.nanoTimeMaybe();
     try {
       return super.getDigest(path);
     } finally {
       profiler.logSimpleTask(startTime, ProfilerTask.VFS_MD5, name);
     }
   }

   @Override
   protected void createFSDependentHardLink(Path linkPath, Path originalPath)
       throws IOException {
     NativePosixFiles.link(originalPath.toString(), linkPath.toString());
   }

   @Override
   public void deleteTreesBelow(Path dir) throws IOException {
     if (dir.isDirectory(Symlinks.NOFOLLOW)) {
       long startTime = Profiler.nanoTimeMaybe();
       try {
         NativePosixFiles.deleteTreesBelow(dir.toString());
       } finally {
         profiler.logSimpleTask(startTime, ProfilerTask.VFS_DELETE, dir.toString());
       }
     }
   }

   private static File createJavaIoFile(Path path) throws FileNotFoundException {
     final String pathStr = path.getPathString();
     if (pathStr.chars().allMatch(c -> c < 128)) {
       return new File(pathStr);
     }

     // Paths returned from NativePosixFiles are Strings containing raw bytes from the filesystem.
     // Java's IO subsystem expects paths to be encoded per the `sun.jnu.encoding` setting. This
     // is difficult to handle generically, but we can special-case the most common case (UTF-8).
     if ("UTF-8".equals(System.getProperty("sun.jnu.encoding"))) {
       final byte[] pathBytes = pathStr.getBytes(StandardCharsets.ISO_8859_1);
       return new File(new String(pathBytes, StandardCharsets.UTF_8));
     }

     // This will probably fail but not much that can be done without migrating to `java.nio.Files`.
     return new File(pathStr);
   }

   @Override
   protected InputStream createFileInputStream(Path path) throws IOException {
     return new FileInputStream(createJavaIoFile(path));
   }

   @Override
   protected OutputStream createFileOutputStream(Path path, boolean append)
       throws FileNotFoundException {
     final String name = path.toString();
     if (profiler.isActive()
         && (profiler.isProfiling(ProfilerTask.VFS_WRITE)
             || profiler.isProfiling(ProfilerTask.VFS_OPEN))) {
       long startTime = Profiler.nanoTimeMaybe();
       try {
         return new ProfiledNativeFileOutputStream(NativePosixFiles.openWrite(name, append), name);
       } finally {
         profiler.logSimpleTask(startTime, ProfilerTask.VFS_OPEN, name);
       }
     } else {
       return new NativeFileOutputStream(NativePosixFiles.openWrite(name, append));
     }
   }

   private static class NativeFileOutputStream extends OutputStream {
     private final int fd;
     private boolean closed = false;

     NativeFileOutputStream(int fd) {
       this.fd = fd;
     }

     @Override
     protected void finalize() throws Throwable {
       close();
       super.finalize();
     }

     @Override
     public synchronized void close() throws IOException {
       if (!closed) {
         NativePosixFiles.close(fd, this);
         closed = true;
       }
       super.close();
     }

     @Override
     public void write(int b) throws IOException {
       write(new byte[] {(byte) (b & 0xFF)});
     }

     @Override
     public void write(byte[] b) throws IOException {
       write(b, 0, b.length);
     }

     @Override
     public synchronized void write(byte[] b, int off, int len) throws IOException {
       if (closed) {
         throw new IOException("attempt to write to a closed Outputstream backed by a native file");
       }
       NativePosixFiles.write(fd, b, off, len);
     }
   }

   private static final class ProfiledNativeFileOutputStream extends NativeFileOutputStream {
     private final String name;

     public ProfiledNativeFileOutputStream(int fd, String name) throws FileNotFoundException {
       super(fd);
       this.name = name;
     }

     @Override
     public synchronized void write(byte[] b, int off, int len) throws IOException {
       long startTime = Profiler.nanoTimeMaybe();
       try {
         super.write(b, off, len);
       } finally {
         profiler.logSimpleTask(startTime, ProfilerTask.VFS_WRITE, name);
       }
     }
   }
 }
	// Copyright 2014 The Bazel Authors. All rights reserved.
	//
	// Licensed under the Apache License, Version 2.0 (the "License");
	// you may not use this file except in compliance with the License.
	// You may obtain a copy of the License at
	//
	// http://www.apache.org/licenses/LICENSE-2.0
	//
	// Unless required by applicable law or agreed to in writing, software
	// distributed under the License is distributed on an "AS IS" BASIS,
	// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	// See the License for the specific language governing permissions and
	// limitations under the License.
	package com.google.devtools.build.lib.unix;

	import com.google.common.annotations.VisibleForTesting;
	import com.google.common.base.Preconditions;
	import com.google.common.collect.Lists;
	import com.google.devtools.build.lib.concurrent.ThreadSafety.ThreadSafe;
	import com.google.devtools.build.lib.profiler.Profiler;
	import com.google.devtools.build.lib.profiler.ProfilerTask;
	import com.google.devtools.build.lib.unix.NativePosixFiles.Dirents;
	import com.google.devtools.build.lib.unix.NativePosixFiles.ReadTypes;
	import com.google.devtools.build.lib.vfs.AbstractFileSystemWithCustomStat;
	import com.google.devtools.build.lib.vfs.DigestHashFunction;
	import com.google.devtools.build.lib.vfs.DigestHashFunction.DefaultHashFunctionNotSetException;
	import com.google.devtools.build.lib.vfs.Dirent;
	import com.google.devtools.build.lib.vfs.FileStatus;
	import com.google.devtools.build.lib.vfs.Path;
	import com.google.devtools.build.lib.vfs.PathFragment;
	import com.google.devtools.build.lib.vfs.Symlinks;
	import java.io.File;
	import java.io.FileInputStream;
	import java.io.FileNotFoundException;
	import java.io.IOException;
	import java.io.InputStream;
	import java.io.OutputStream;
	import java.nio.charset.StandardCharsets;
	import java.util.ArrayList;
	import java.util.Collection;
	import java.util.List;

	/**
	* This class implements the FileSystem interface using direct calls to the UNIX filesystem.
	*/
	@ThreadSafe
	public class UnixFileSystem extends AbstractFileSystemWithCustomStat {

	public UnixFileSystem() throws DefaultHashFunctionNotSetException {}

	public UnixFileSystem(DigestHashFunction hashFunction) {
	super(hashFunction);
	}

	/**
	* Eager implementation of FileStatus for file systems that have an atomic
	* stat(2) syscall. A proxy for {@link com.google.devtools.build.lib.unix.FileStatus}.
	* Note that isFile and getLastModifiedTime have slightly different meanings
	* between UNIX and VFS.
	*/
	@VisibleForTesting
	protected static class UnixFileStatus implements FileStatus {

	private final com.google.devtools.build.lib.unix.FileStatus status;

	UnixFileStatus(com.google.devtools.build.lib.unix.FileStatus status) {
	this.status = status;
	}

	@Override
	public boolean isFile() { return !isDirectory() && !isSymbolicLink(); }

	@Override
	public boolean isDirectory() { return status.isDirectory(); }

	@Override
	public boolean isSymbolicLink() { return status.isSymbolicLink(); }

	@Override
	public boolean isSpecialFile() { return isFile() && !status.isRegularFile(); }

	@Override
	public long getSize() { return status.getSize(); }

	@Override
	public long getLastModifiedTime() {
	return (status.getLastModifiedTime() * 1000)
	+ (status.getFractionalLastModifiedTime() / 1000000);
	}

	@Override
	public long getLastChangeTime() {
	return (status.getLastChangeTime() * 1000)
	+ (status.getFractionalLastChangeTime() / 1000000);
	}

	@Override
	public long getNodeId() {
	// Note that we may want to include more information in this id number going forward,
	// especially the device number.
	return status.getInodeNumber();
	}

	int getPermissions() { return status.getPermissions(); }

	@Override
	public String toString() { return status.toString(); }
	}

	@Override
	protected Collection<String> getDirectoryEntries(Path path) throws IOException {
	String name = path.getPathString();
	String[] entries;
	long startTime = Profiler.nanoTimeMaybe();
	try {
	entries = NativePosixFiles.readdir(name);
	} finally {
	profiler.logSimpleTask(startTime, ProfilerTask.VFS_DIR, name);
	}
	Collection<String> result = new ArrayList<>(entries.length);
	for (String entry : entries) {
	result.add(entry);
	}
	return result;
	}

	@Override
	protected PathFragment resolveOneLink(Path path) throws IOException {
	// Beware, this seemingly simple code belies the complex specification of
	// FileSystem.resolveOneLink().
	return stat(path, false).isSymbolicLink()
	? readSymbolicLink(path)
	: null;
	}

	/**
	* Converts from {@link com.google.devtools.build.lib.unix.NativePosixFiles.Dirents.Type} to
	* {@link com.google.devtools.build.lib.vfs.Dirent.Type}.
	*/
	private static Dirent.Type convertToDirentType(Dirents.Type type) {
	switch (type) {
	case FILE:
	return Dirent.Type.FILE;
	case DIRECTORY:
	return Dirent.Type.DIRECTORY;
	case SYMLINK:
	return Dirent.Type.SYMLINK;
	case UNKNOWN:
	return Dirent.Type.UNKNOWN;
	default:
	throw new IllegalArgumentException("Unknown type " + type);
	}
	}

	@Override
	protected Collection<Dirent> readdir(Path path, boolean followSymlinks) throws IOException {
	String name = path.getPathString();
	long startTime = Profiler.nanoTimeMaybe();
	try {
	Dirents unixDirents = NativePosixFiles.readdir(name,
	followSymlinks ? ReadTypes.FOLLOW : ReadTypes.NOFOLLOW);
	Preconditions.checkState(unixDirents.hasTypes());
	List<Dirent> dirents = Lists.newArrayListWithCapacity(unixDirents.size());
	for (int i = 0; i < unixDirents.size(); i++) {
	dirents.add(new Dirent(unixDirents.getName(i),
	convertToDirentType(unixDirents.getType(i))));
	}
	return dirents;
	} finally {
	profiler.logSimpleTask(startTime, ProfilerTask.VFS_DIR, name);
	}
	}

	@Override
	protected FileStatus stat(Path path, boolean followSymlinks) throws IOException {
	return statInternal(path, followSymlinks);
	}

	@VisibleForTesting
	protected UnixFileStatus statInternal(Path path, boolean followSymlinks) throws IOException {
	String name = path.getPathString();
	long startTime = Profiler.nanoTimeMaybe();
	try {
	return new UnixFileStatus(followSymlinks
	? NativePosixFiles.stat(name)
	: NativePosixFiles.lstat(name));
	} finally {
	profiler.logSimpleTask(startTime, ProfilerTask.VFS_STAT, name);
	}
	}

	// Like stat(), but returns null instead of throwing.
	// This is a performance optimization in the case where clients
	// catch and don't re-throw.
	@Override
	protected FileStatus statNullable(Path path, boolean followSymlinks) {
	String name = path.getPathString();
	long startTime = Profiler.nanoTimeMaybe();
	try {
	ErrnoFileStatus stat = followSymlinks
	? NativePosixFiles.errnoStat(name)
	: NativePosixFiles.errnoLstat(name);
	return stat.hasError() ? null : new UnixFileStatus(stat);
	} finally {
	profiler.logSimpleTask(startTime, ProfilerTask.VFS_STAT, name);
	}
	}

	@Override
	protected boolean exists(Path path, boolean followSymlinks) {
	return statNullable(path, followSymlinks) != null;
	}

	/**
	* Return true iff the {@code stat} of {@code path} resulted in an {@code ENOENT}
	* or {@code ENOTDIR} error.
	*/
	@Override
	protected FileStatus statIfFound(Path path, boolean followSymlinks) throws IOException {
	String name = path.getPathString();
	long startTime = Profiler.nanoTimeMaybe();
	try {
	ErrnoFileStatus stat = followSymlinks
	? NativePosixFiles.errnoStat(name)
	: NativePosixFiles.errnoLstat(name);
	if (!stat.hasError()) {
	return new UnixFileStatus(stat);
	}
	int errno = stat.getErrno();
	if (errno == ErrnoFileStatus.ENOENT \|\| errno == ErrnoFileStatus.ENOTDIR) {
	return null;
	}
	// This should not return -- we are calling stat here just to throw the proper exception.
	// However, since there may be transient IO errors, we cannot guarantee that an exception will
	// be thrown.
	// TODO(bazel-team): Extract the exception-construction code and make it visible separately in
	// FilesystemUtils to avoid having to do a duplicate stat call.
	return stat(path, followSymlinks);
	} finally {
	profiler.logSimpleTask(startTime, ProfilerTask.VFS_STAT, name);
	}
	}

	@Override
	protected boolean isReadable(Path path) throws IOException {
	return (statInternal(path, true).getPermissions() & 0400) != 0;
	}

	@Override
	protected boolean isWritable(Path path) throws IOException {
	return (statInternal(path, true).getPermissions() & 0200) != 0;
	}

	@Override
	protected boolean isExecutable(Path path) throws IOException {
	return (statInternal(path, true).getPermissions() & 0100) != 0;
	}

	/**
	* Adds or remove the bits specified in "permissionBits" to the permission
	* mask of the file specified by {@code path}. If the argument {@code add} is
	* true, the specified permissions are added, otherwise they are removed.
	*
	* @throws IOException if there was an error writing the file's metadata
	*/
	private void modifyPermissionBits(Path path, int permissionBits, boolean add)
	throws IOException {
	int oldMode = statInternal(path, true).getPermissions();
	int newMode = add ? (oldMode \| permissionBits) : (oldMode & ~permissionBits);
	NativePosixFiles.chmod(path.toString(), newMode);
	}

	@Override
	protected void setReadable(Path path, boolean readable) throws IOException {
	modifyPermissionBits(path, 0400, readable);
	}

	@Override
	public void setWritable(Path path, boolean writable) throws IOException {
	modifyPermissionBits(path, 0200, writable);
	}

	@Override
	protected void setExecutable(Path path, boolean executable) throws IOException {
	modifyPermissionBits(path, 0111, executable);
	}

	@Override
	protected void chmod(Path path, int mode) throws IOException {
	NativePosixFiles.chmod(path.toString(), mode);
	}

	@Override
	public boolean supportsModifications(Path path) {
	return true;
	}

	@Override
	public boolean supportsSymbolicLinksNatively(Path path) {
	return true;
	}

	@Override
	public boolean supportsHardLinksNatively(Path path) {
	return true;
	}

	@Override
	public boolean isFilePathCaseSensitive() {
	return true;
	}

	@Override
	public boolean createDirectory(Path path) throws IOException {
	// Note: UNIX mkdir(2), FilesystemUtils.mkdir() and createDirectory all
	// have different ways of representing failure!
	if (NativePosixFiles.mkdir(path.toString(), 0777)) {
	return true; // successfully created
	}

	// false => EEXIST: something is already in the way (file/dir/symlink)
	if (isDirectory(path, false)) {
	return false; // directory already existed
	} else {
	throw new IOException(path + " (File exists)");
	}
	}

	@Override
	public void createDirectoryAndParents(Path path) throws IOException {
	NativePosixFiles.mkdirs(path.toString(), 0777);
	}

	@Override
	protected void createSymbolicLink(Path linkPath, PathFragment targetFragment)
	throws IOException {
	NativePosixFiles.symlink(targetFragment.getSafePathString(), linkPath.toString());
	}

	@Override
	protected PathFragment readSymbolicLink(Path path) throws IOException {
	// Note that the default implementation of readSymbolicLinkUnchecked calls this method and thus
	// is optimal since we only make one system call in here.
	String name = path.toString();
	long startTime = Profiler.nanoTimeMaybe();
	try {
	return PathFragment.create(NativePosixFiles.readlink(name));
	} catch (IOException e) {
	// EINVAL => not a symbolic link. Anything else is a real error.
	throw e.getMessage().endsWith("(Invalid argument)") ? new NotASymlinkException(path) : e;
	} finally {
	profiler.logSimpleTask(startTime, ProfilerTask.VFS_READLINK, name);
	}
	}

	@Override
	public void renameTo(Path sourcePath, Path targetPath) throws IOException {
	NativePosixFiles.rename(sourcePath.toString(), targetPath.toString());
	}

	@Override
	protected long getFileSize(Path path, boolean followSymlinks) throws IOException {
	return stat(path, followSymlinks).getSize();
	}

	@Override
	public boolean delete(Path path) throws IOException {
	String name = path.toString();
	long startTime = Profiler.nanoTimeMaybe();
	try {
	return NativePosixFiles.remove(name);
	} finally {
	profiler.logSimpleTask(startTime, ProfilerTask.VFS_DELETE, name);
	}
	}

	@Override
	protected long getLastModifiedTime(Path path, boolean followSymlinks) throws IOException {
	return stat(path, followSymlinks).getLastModifiedTime();
	}

	@Override
	public void setLastModifiedTime(Path path, long newTime) throws IOException {
	if (newTime == -1L) { // "now"
	NativePosixFiles.utime(path.toString(), true, 0);
	} else {
	// newTime > MAX_INT => -ve unixTime
	int unixTime = (int) (newTime / 1000);
	NativePosixFiles.utime(path.toString(), false, unixTime);
	}
	}

	@Override
	public byte[] getxattr(Path path, String name, boolean followSymlinks) throws IOException {
	String pathName = path.toString();
	long startTime = Profiler.nanoTimeMaybe();
	try {
	return followSymlinks
	? NativePosixFiles.getxattr(pathName, name)
	: NativePosixFiles.lgetxattr(pathName, name);
	} catch (UnsupportedOperationException e) {
	// getxattr() syscall is not supported by the underlying filesystem (it returned ENOTSUP).
	// Per method contract, treat this as ENODATA.
	return null;
	} finally {
	profiler.logSimpleTask(startTime, ProfilerTask.VFS_XATTR, pathName);
	}
	}

	@Override
	protected byte[] getDigest(Path path) throws IOException {
	String name = path.toString();
	long startTime = Profiler.nanoTimeMaybe();
	try {
	return super.getDigest(path);
	} finally {
	profiler.logSimpleTask(startTime, ProfilerTask.VFS_MD5, name);
	}
	}

	@Override
	protected void createFSDependentHardLink(Path linkPath, Path originalPath)
	throws IOException {
	NativePosixFiles.link(originalPath.toString(), linkPath.toString());
	}

	@Override
	public void deleteTreesBelow(Path dir) throws IOException {
	if (dir.isDirectory(Symlinks.NOFOLLOW)) {
	long startTime = Profiler.nanoTimeMaybe();
	try {
	NativePosixFiles.deleteTreesBelow(dir.toString());
	} finally {
	profiler.logSimpleTask(startTime, ProfilerTask.VFS_DELETE, dir.toString());
	}
	}
	}

	private static File createJavaIoFile(Path path) throws FileNotFoundException {
	final String pathStr = path.getPathString();
	if (pathStr.chars().allMatch(c -> c < 128)) {
	return new File(pathStr);
	}

	// Paths returned from NativePosixFiles are Strings containing raw bytes from the filesystem.
	// Java's IO subsystem expects paths to be encoded per the `sun.jnu.encoding` setting. This
	// is difficult to handle generically, but we can special-case the most common case (UTF-8).
	if ("UTF-8".equals(System.getProperty("sun.jnu.encoding"))) {
	final byte[] pathBytes = pathStr.getBytes(StandardCharsets.ISO_8859_1);
	return new File(new String(pathBytes, StandardCharsets.UTF_8));
	}

	// This will probably fail but not much that can be done without migrating to `java.nio.Files`.
	return new File(pathStr);
	}

	@Override
	protected InputStream createFileInputStream(Path path) throws IOException {
	return new FileInputStream(createJavaIoFile(path));
	}

	@Override
	protected OutputStream createFileOutputStream(Path path, boolean append)
	throws FileNotFoundException {
	final String name = path.toString();
	if (profiler.isActive()
	&& (profiler.isProfiling(ProfilerTask.VFS_WRITE)
	\|\| profiler.isProfiling(ProfilerTask.VFS_OPEN))) {
	long startTime = Profiler.nanoTimeMaybe();
	try {
	return new ProfiledNativeFileOutputStream(NativePosixFiles.openWrite(name, append), name);
	} finally {
	profiler.logSimpleTask(startTime, ProfilerTask.VFS_OPEN, name);
	}
	} else {
	return new NativeFileOutputStream(NativePosixFiles.openWrite(name, append));
	}
	}

	private static class NativeFileOutputStream extends OutputStream {
	private final int fd;
	private boolean closed = false;

	NativeFileOutputStream(int fd) {
	this.fd = fd;
	}

	@Override
	protected void finalize() throws Throwable {
	close();
	super.finalize();
	}

	@Override
	public synchronized void close() throws IOException {
	if (!closed) {
	NativePosixFiles.close(fd, this);
	closed = true;
	}
	super.close();
	}

	@Override
	public void write(int b) throws IOException {
	write(new byte[] {(byte) (b & 0xFF)});
	}

	@Override
	public void write(byte[] b) throws IOException {
	write(b, 0, b.length);
	}

	@Override
	public synchronized void write(byte[] b, int off, int len) throws IOException {
	if (closed) {
	throw new IOException("attempt to write to a closed Outputstream backed by a native file");
	}
	NativePosixFiles.write(fd, b, off, len);
	}
	}

	private static final class ProfiledNativeFileOutputStream extends NativeFileOutputStream {
	private final String name;

	public ProfiledNativeFileOutputStream(int fd, String name) throws FileNotFoundException {
	super(fd);
	this.name = name;
	}

	@Override
	public synchronized void write(byte[] b, int off, int len) throws IOException {
	long startTime = Profiler.nanoTimeMaybe();
	try {
	super.write(b, off, len);
	} finally {
	profiler.logSimpleTask(startTime, ProfilerTask.VFS_WRITE, name);
	}
	}
	}
	}