llvm-project

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//===- FileSystemStatCache.cpp - Caching for 'stat' calls -----------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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//  This file defines the FileSystemStatCache interface.
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//
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//===----------------------------------------------------------------------===//
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#include "clang/Basic/FileSystemStatCache.h"
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#include "llvm/Support/Chrono.h"
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#include "llvm/Support/ErrorOr.h"
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#include "llvm/Support/Path.h"
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#include "llvm/Support/VirtualFileSystem.h"
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#include <utility>
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using namespace clang;
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void FileSystemStatCache::anchor() {}
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/// FileSystemStatCache::get - Get the 'stat' information for the specified
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/// path, using the cache to accelerate it if possible.  This returns true if
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/// the path does not exist or false if it exists.
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///
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/// If isFile is true, then this lookup should only return success for files
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/// (not directories).  If it is false this lookup should only return
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/// success for directories (not files).  On a successful file lookup, the
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/// implementation can optionally fill in FileDescriptor with a valid
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/// descriptor and the client guarantees that it will close it.
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std::error_code
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FileSystemStatCache::get(StringRef Path, llvm::vfs::Status &Status,
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                         bool isFile, std::unique_ptr<llvm::vfs::File> *F,
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                         FileSystemStatCache *Cache,
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                         llvm::vfs::FileSystem &FS) {
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  bool isForDir = !isFile;
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  std::error_code RetCode;
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  // If we have a cache, use it to resolve the stat query.
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  if (Cache)
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    RetCode = Cache->getStat(Path, Status, isFile, F, FS);
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  else if (isForDir || !F) {
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    // If this is a directory or a file descriptor is not needed and we have
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    // no cache, just go to the file system.
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    llvm::ErrorOr<llvm::vfs::Status> StatusOrErr = FS.status(Path);
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    if (!StatusOrErr) {
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      RetCode = StatusOrErr.getError();
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    } else {
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      Status = *StatusOrErr;
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    }
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  } else {
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    // Otherwise, we have to go to the filesystem.  We can always just use
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    // 'stat' here, but (for files) the client is asking whether the file exists
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    // because it wants to turn around and *open* it.  It is more efficient to
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    // do "open+fstat" on success than it is to do "stat+open".
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    //
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    // Because of this, check to see if the file exists with 'open'.  If the
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    // open succeeds, use fstat to get the stat info.
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    auto OwnedFile = FS.openFileForRead(Path);
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    if (!OwnedFile) {
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      // If the open fails, our "stat" fails.
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      RetCode = OwnedFile.getError();
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    } else {
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      // Otherwise, the open succeeded.  Do an fstat to get the information
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      // about the file.  We'll end up returning the open file descriptor to the
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      // client to do what they please with it.
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      llvm::ErrorOr<llvm::vfs::Status> StatusOrErr = (*OwnedFile)->status();
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      if (StatusOrErr) {
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        Status = *StatusOrErr;
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        *F = std::move(*OwnedFile);
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      } else {
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        // fstat rarely fails.  If it does, claim the initial open didn't
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        // succeed.
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        *F = nullptr;
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        RetCode = StatusOrErr.getError();
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      }
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    }
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  }
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  // If the path doesn't exist, return failure.
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  if (RetCode)
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    return RetCode;
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  // If the path exists, make sure that its "directoryness" matches the clients
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  // demands.
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  if (Status.isDirectory() != isForDir) {
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    // If not, close the file if opened.
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    if (F)
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      *F = nullptr;
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    return std::make_error_code(
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        Status.isDirectory() ?
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            std::errc::is_a_directory : std::errc::not_a_directory);
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  }
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  return std::error_code();
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}
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std::error_code
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MemorizeStatCalls::getStat(StringRef Path, llvm::vfs::Status &Status,
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                           bool isFile,
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                           std::unique_ptr<llvm::vfs::File> *F,
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                           llvm::vfs::FileSystem &FS) {
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  auto err = get(Path, Status, isFile, F, nullptr, FS);
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  if (err) {
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    // Do not cache failed stats, it is easy to construct common inconsistent
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    // situations if we do, and they are not important for PCH performance
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    // (which currently only needs the stats to construct the initial
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    // FileManager entries).
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    return err;
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  }
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  // Cache file 'stat' results and directories with absolutely paths.
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  if (!Status.isDirectory() || llvm::sys::path::is_absolute(Path))
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    StatCalls[Path] = Status;
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  return std::error_code();
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}
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