Disable OS file locking on Fuchsia

Fuchsia doesn't support file locking, i.e. there is no
base::File::Lock(), so components/filesystem was failing to compile.
Added ifdefs so File::Lock() is not used on Fuchsia.

Bug: 737802, 744893
Change-Id: I825fba49b9c6247d1b4c75ca23fce4c150344db1
Reviewed-on: https://chromium-review.googlesource.com/575288
Commit-Queue: Sergey Ulanov <sergeyu@chromium.org>
Reviewed-by: Kevin Marshall <kmarshall@chromium.org>
Reviewed-by: Elliot Glaysher <erg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#487347}

components/filesystem/file_impl.cc

@@ -62,6 +62,7 @@ bool FileImpl::IsValid() const {
   return file_.IsValid();
 }
 
+#if !defined(OS_FUCHSIA)
 base::File::Error FileImpl::RawLockFile() {
   return file_.Lock();
 }
@@ -69,6 +70,7 @@ base::File::Error FileImpl::RawLockFile() {
 base::File::Error FileImpl::RawUnlockFile() {
   return file_.Unlock();
 }
+#endif  // !OS_FUCHSIA
 
 void FileImpl::Close(CloseCallback callback) {
   if (!file_.IsValid()) {

components/filesystem/file_impl.h

@@ -10,6 +10,7 @@
 #include "base/files/file.h"
 #include "base/files/scoped_file.h"
 #include "base/macros.h"
+#include "build/build_config.h"
 #include "components/filesystem/public/interfaces/directory.mojom.h"
 #include "mojo/public/cpp/bindings/interface_request.h"
 
@@ -37,10 +38,12 @@ class FileImpl : public mojom::File {
   // Returns whether the underlying file handle is valid.
   bool IsValid() const;
 
+#if !defined(OS_FUCHSIA)
   // Attempts to perform the native operating system's locking operations on
-  // the internal mojom::File handle
+  // the internal mojom::File handle. Not supported on Fuchsia.
   base::File::Error RawLockFile();
   base::File::Error RawUnlockFile();
+#endif  // !OS_FUCHSIA
 
   const base::FilePath& path() const { return path_; }
 

components/filesystem/lock_table.cc

@@ -4,6 +4,7 @@
 
 #include "components/filesystem/lock_table.h"
 
+#include "build/build_config.h"
 #include "components/filesystem/file_impl.h"
 
 namespace filesystem {
@@ -22,11 +23,20 @@ base::File::Error LockTable::LockFile(FileImpl* file) {
     return base::File::FILE_ERROR_FAILED;
   }
 
+#if !defined(OS_FUCHSIA)
+  // Fuchsia doesn't provide a file locking mechanism, so file locks work only
+  // within a single process. File locking is used only by LevelDB which stores
+  // all files in the profile directory and normally there shouldn't be more
+  // than a single chrome process per profile. So in-process locks should be
+  // sufficient.
+  // TODO(fuchsia): Investigate if it's necessary to implement cross-process
+  // file locks. crbug.com/744893 .
   base::File::Error lock_err = file->RawLockFile();
   if (lock_err != base::File::FILE_OK) {
     // Locking failed for some reason.
     return lock_err;
   }
+#endif  // !OS_FUCHSIA
 
   locked_files_.insert(file->path());
   return base::File::FILE_OK;
@@ -35,12 +45,14 @@ base::File::Error LockTable::LockFile(FileImpl* file) {
 base::File::Error LockTable::UnlockFile(FileImpl* file) {
   auto it = locked_files_.find(file->path());
   if (it != locked_files_.end()) {
+#if !defined(OS_FUCHSIA)
     base::File::Error lock_err = file->RawUnlockFile();
     if (lock_err != base::File::FILE_OK) {
       // TODO(erg): When can we fail to release a lock?
       NOTREACHED();
       return lock_err;
     }
+#endif  // !OS_FUCHSIA
 
     locked_files_.erase(it);
   }