Add a mini C filesystem wrapper library with mmap support

2 files changed, 106 insertions, 0 deletions

diff --git a/lib/filesystem.cpp b/lib/filesystem.cpp
new file mode 100644
index 0000000..181fb07
--- /dev/null
+++ b/lib/filesystem.cpp
@@ -0,0 +1,64 @@
+#include "filesystem.h"
+#include <fcntl.h>
+#include <filesystem>
+#include <string>
+#include <sys/mman.h>
+#include <system_error>
+#include <unistd.h>
+
+namespace filesystem {
+	template<typename... Args>
+	[[noreturn]] static void
+	throw_filesystem_error(std::string operation, int err, Args &&... args)
+	{
+		throw std::filesystem::filesystem_error {
+				std::move(operation), std::forward<Args>(args)..., std::error_code {err, std::system_category()}};
+	}
+
+	memmap::memmap(size_t length, int prot, int flags, int fd, off_t offset) :
+		addr {mmap(nullptr, length, prot, flags, fd, offset)}, length {length}
+	{
+		if (addr == MAP_FAILED) {
+			throw std::filesystem::filesystem_error {"mmap", std::error_code {errno, std::system_category()}};
+		}
+	}
+
+	memmap::~memmap()
+	{
+		::munmap(addr, length);
+	}
+
+	void
+	memmap::msync(int flags) const
+	{
+		if (::msync(addr, length, flags)) {
+			throw_filesystem_error("msync", errno);
+		}
+	}
+
+	fh::fh(const char * path, int flags, int mode) : h {open(path, flags, mode)}
+	{
+		if (h == -1) {
+			throw_filesystem_error("open", errno, path);
+		}
+	}
+
+	fh::~fh()
+	{
+		::close(h);
+	}
+
+	void
+	fh::truncate(size_t size)
+	{
+		if (::ftruncate(h, static_cast<off_t>(size))) {
+			throw_filesystem_error("ftruncate", errno);
+		}
+	}
+
+	memmap
+	fh::mmap(size_t length, size_t offset, int prot, int flags)
+	{
+		return memmap {length, prot, flags, h, static_cast<off_t>(offset)};
+	}
+}
diff --git a/lib/filesystem.h b/lib/filesystem.h
new file mode 100644
index 0000000..0c44236
--- /dev/null
+++ b/lib/filesystem.h
@@ -0,0 +1,42 @@
+#pragma once
+
+#include "special_members.hpp"
+#include <cstddef>
+#include <sys/types.h>
+
+namespace filesystem {
+	class [[nodiscard]] memmap final {
+	public:
+		memmap(size_t length, int prot, int flags, int fd, off_t offset);
+		~memmap();
+		NO_MOVE(memmap);
+		NO_COPY(memmap);
+
+		template<typename T>
+		T *
+		get()
+		{
+			return static_cast<T *>(addr);
+		}
+
+		void msync(int flags) const;
+
+	private:
+		void * addr;
+		size_t length;
+	};
+
+	class [[nodiscard]] fh final {
+	public:
+		fh(const char * path, int flags, int mode);
+		~fh();
+		NO_MOVE(fh);
+		NO_COPY(fh);
+
+		void truncate(size_t size);
+		memmap mmap(size_t length, size_t offset, int prot, int flags);
+
+	private:
+		int h;
+	};
+}