Implemented filecas.cpp for POSIX platforms

1 files changed, 92 insertions, 2 deletions

diff --git a/zenstore/filecas.cpp b/zenstore/filecas.cpp
index 3eccf53ff..6d385a208 100644
--- a/zenstore/filecas.cpp
+++ b/zenstore/filecas.cpp
@@ -86,6 +86,9 @@ FileCasStrategy::InsertChunk(IoBuffer Chunk, const IoHash& ChunkHash)
 	{
 		ShardingHelper Name(m_Config.RootDirectory.c_str(), ChunkHash);
 
+		RwLock::ExclusiveLockScope _(LockForHash(ChunkHash));
+
+#if ZEN_PLATFORM_WINDOWS
 		const HANDLE ChunkFileHandle = FileRef.FileHandle;
 
 		auto DeletePayloadFileOnClose = [&] {
@@ -106,8 +109,6 @@ FileCasStrategy::InsertChunk(IoBuffer Chunk, const IoHash& ChunkHash)
 		//
 		// Future improvement: maintain Bloom filter to avoid expensive file system probes?
 
-		RwLock::ExclusiveLockScope _(LockForHash(ChunkHash));
-
 		{
 			CAtlFile PayloadFile;
 
@@ -226,6 +227,49 @@ FileCasStrategy::InsertChunk(IoBuffer Chunk, const IoHash& ChunkHash)
 				 ChunkHash);
 
 		DeletePayloadFileOnClose();
+#elif ZEN_PLATFORM_LINUX
+		std::filesystem::path SourcePath = PathFromHandle(FileRef.FileHandle);
+		std::filesystem::path DestPath = Name.ShardedPath.c_str();
+		int Ret = link(SourcePath.c_str(), DestPath.c_str());
+		if (Ret < 0 && zen::GetLastError() == ENOENT)
+		{
+			// Destination directory doesn't exist. Create it any try again.
+			CreateDirectories(DestPath.parent_path().c_str());
+			Ret = link(SourcePath.c_str(), DestPath.c_str());
+		}
+		int LinkError = zen::GetLastError();
+
+		// Unlink the file. If the path to unlink didn't exist someone else
+		// beat us to it and that is hunky-dory.
+		if (unlink(SourcePath.c_str()) < 0)
+		{
+			int UnlinkError = zen::GetLastError();
+			if (UnlinkError != ENOENT)
+			{
+				ZEN_WARN("unlink of CAS payload file failed ('{}')", GetSystemErrorAsString(UnlinkError));
+			}
+		}
+
+		// It is possible that someone beat us to it in linking the file. In that
+		// case a "file exists" error is okay. All others are not.
+		if (Ret < 0)
+		{
+			if (LinkError == EEXIST)
+			{
+				return CasStore::InsertResult{.New = false};
+			}
+
+			ZEN_WARN("link of CAS payload file failed ('{}'), falling back to regular write for insert of {}",
+					GetSystemErrorAsString(LinkError),
+					ChunkHash);
+		}
+		else
+		{
+			return CasStore::InsertResult{.New = true};
+		}
+#else
+#	error check link/unlink for this platform
+#endif // ZEN_PLATFORM_*
 	}
 
 	return InsertChunk(Chunk.Data(), Chunk.Size(), ChunkHash);
@@ -240,6 +284,7 @@ FileCasStrategy::InsertChunk(const void* const ChunkData, const size_t ChunkSize
 	//
 	// Future improvement: maintain Bloom filter to avoid expensive file system probes?
 
+#if ZEN_PLATFORM_WINDOWS
 	CAtlFile PayloadFile;
 
 	HRESULT hRes = PayloadFile.Create(Name.ShardedPath.c_str(), GENERIC_READ, FILE_SHARE_READ, OPEN_EXISTING);
@@ -252,9 +297,18 @@ FileCasStrategy::InsertChunk(const void* const ChunkData, const size_t ChunkSize
 	}
 
 	PayloadFile.Close();
+#elif ZEN_PLATFORM_LINUX
+	if (access(Name.ShardedPath.c_str(), F_OK) == 0)
+	{
+		return CasStore::InsertResult{.New = false};
+	}
+#else
+#	error Check access() for this platform
+#endif
 
 	RwLock::ExclusiveLockScope _(LockForHash(ChunkHash));
 
+#if ZEN_PLATFORM_WINDOWS
 	// For now, use double-checked locking to see if someone else was first
 
 	hRes = PayloadFile.Create(Name.ShardedPath.c_str(), GENERIC_READ, FILE_SHARE_READ, OPEN_EXISTING);
@@ -288,6 +342,42 @@ FileCasStrategy::InsertChunk(const void* const ChunkData, const size_t ChunkSize
 	{
 		ThrowSystemException(hRes, "Failed to open shard file '{}'"_format(WideToUtf8(Name.ShardedPath)));
 	}
+#else
+	// Attempt to exclusively create the file.
+	auto InternalCreateFile = [&] { return open(Name.ShardedPath.c_str(), O_WRONLY|O_CREAT|O_EXCL, 0666); };
+	int Fd = InternalCreateFile();
+	if (Fd < 0)
+	{
+		switch (zen::GetLastError())
+		{
+		case EEXIST:
+			// Another thread has beat us to it so we're golden.
+			return {.New = false};
+
+		case ENOENT:
+			if (zen::CreateDirectories(std::string_view(Name.ShardedPath.c_str(), Name.Shard2len)))
+			{
+				Fd = InternalCreateFile();
+				if (Fd >= 0)
+				{
+					break;
+				}
+			}
+			ThrowLastError("Failed creating shard directory '{}'"_format(Name.ShardedPath));
+
+		default:
+			ThrowLastError("Unexpected error occurred opening shard file '{}'"_format(Name.ShardedPath));
+		}
+	}
+
+	struct FdWrapper
+	{
+			 ~FdWrapper()							{ Close(); }
+		void Write(const void* Cursor, size_t Size) { (void)!write(Fd, Cursor, Size); }
+		void Close()								{ if (Fd >= 0) { close(Fd); Fd = -1; } }
+		int	 Fd;
+	} PayloadFile = { Fd };
+#endif // ZEN_PLATFORM_WINDOWS
 
 	size_t ChunkRemain = ChunkSize;
 	auto   ChunkCursor = reinterpret_cast<const uint8_t*>(ChunkData);