From f4fa52d7633d9d67d4c41f76b0e317c6232eb907 Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Sun, 11 Dec 2022 12:39:26 +0000
Subject: Add a mini C filesystem wrapper library with mmap support

---
 gfx/models/texture.cpp | 18 ++++++--------
 lib/filesystem.cpp     | 64 ++++++++++++++++++++++++++++++++++++++++++++++++++
 lib/filesystem.h       | 42 +++++++++++++++++++++++++++++++++
 3 files changed, 113 insertions(+), 11 deletions(-)
 create mode 100644 lib/filesystem.cpp
 create mode 100644 lib/filesystem.h

diff --git a/gfx/models/texture.cpp b/gfx/models/texture.cpp
index 5b8d376..6019bec 100644
--- a/gfx/models/texture.cpp
+++ b/gfx/models/texture.cpp
@@ -3,6 +3,7 @@
 #include <GL/glew.h>
 #include <cache.h>
 #include <fcntl.h>
+#include <filesystem.h>
 #include <gfx/image.h>
 #include <glm/geometric.hpp>
 #include <resource.h>
@@ -50,18 +51,13 @@ Texture::save(const glTexture & texture, GLenum format, const glm::ivec2 & size,
 	size_t dataSize = (static_cast<size_t>(size.x * size.y * channels));
 	size_t fileSize = dataSize + sizeof(TGAHead);
 
-	auto out = open(path, O_RDWR | O_CREAT, 0660);
-	std::ignore = ftruncate(out, static_cast<off_t>(fileSize));
-	TGAHead * tga = static_cast<TGAHead *>(mmap(nullptr, fileSize, PROT_WRITE, MAP_SHARED, out, 0));
-	close(out);
-	if (tga == MAP_FAILED) {
-		return;
-	}
-	*tga = {0, tgaFormat, 0, 0, 0, 0, static_cast<short>(size.x), static_cast<short>(size.y),
+	filesystem::fh out {path, O_RDWR | O_CREAT, 0660};
+	out.truncate(fileSize);
+	auto tga = out.mmap(fileSize, 0, PROT_WRITE, MAP_SHARED);
+	*tga.get<TGAHead>() = {0, tgaFormat, 0, 0, 0, 0, static_cast<short>(size.x), static_cast<short>(size.y),
 			static_cast<short>(8 * channels)};
-	glGetTextureImage(texture, 0, format, GL_UNSIGNED_BYTE, static_cast<GLsizei>(dataSize), tga + 1);
-	msync(tga, fileSize, MS_ASYNC);
-	munmap(tga, fileSize);
+	glGetTextureImage(texture, 0, format, GL_UNSIGNED_BYTE, static_cast<GLsizei>(dataSize), tga.get<TGAHead>() + 1);
+	tga.msync(MS_ASYNC);
 }
 
 void
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;
+	};
+}
-- 
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