Added `cow_create_fd(fd, size)`: Create a `cow_t*` over an already existing file descriptor

Fortune for libcow's current commit: Half curse − 半凶

Makefile

@@ -5,7 +5,7 @@ PROJECT=cow
 AUTHOR=Avril (Flanchan) <flanchan@cumallover.me>
 
 VERSION_MAJOR=0
-VERSION_MINOR=2.0
+VERSION_MINOR=3.0
 VERSION=$(VERSION_MAJOR).$(VERSION_MINOR)
 
 ifeq ($(PREFIX),)

include/cow.h

@@ -35,6 +35,13 @@ typedef struct cow_mapped_slice cow_t;
 /// Writes to this instance pointer (`cow_ptr()`) are written to the allocated memory.
 /// Writes to any cloned instances do not propagate to this instance.
 cow_t* cow_create(size_t size);
+/// Create a new copy-on-write area of `size` bytes from file `fd`. 
+/// Writes to this instance pointer (`cow_ptr()`) are written to the allocated memory.
+/// Writes to any cloned instances do not propagate to this instance.
+///
+/// The resulting object does not own `fd`, but does own a duplicate of it.
+cow_t* cow_create_fd(int fd, size_t size);
+
 /// Free a cow area. This should be called on all clones before the parent of those clones is freed.
 void cow_free(cow_t* restrict cow);
 /// Create a clone of this instance. Any writes to the returned pointer will not be propagated to the input one.

include/cow.hpp

@@ -21,7 +21,9 @@ struct Cow : public _cow_util::Span<unsigned char> {
 	struct Fake;
 	Cow() = delete;
 
+	Cow(int fd, size_t size);
 	explicit Cow(size_t size);
+
 	Cow(Cow&& m);
 	virtual ~Cow();
 

src/cow.c

@@ -76,13 +76,13 @@ size_t cow_size(const cow_t* cow)
 	return cow->size;
 }
 
-inline internal cow_t _cow_create_unboxed(size_t size)
+inline internal cow_t _cow_create_unboxed(int _fd, size_t size)
 {
 	cow_t ret;
 
 	ret.size = size;
 	if( (ret.poisoned = 
-		((ret.fd = shm_fd(size)) == -1))
+		((ret.fd = _fd < 0 ? shm_fd(size) : _fd) == -1))
 	) {
 		ret.origin = NULL;
 		return ret;
@@ -96,7 +96,14 @@ inline internal cow_t _cow_create_unboxed(size_t size)
 }
 cow_t* cow_create(size_t size)
 {	
-	return box_value(_cow_create_unboxed(size));
+	return box_value(_cow_create_unboxed(-1, size));
+}
+
+cow_t* cow_create_fd(int fd, size_t size)
+{
+	fd = dup(fd);
+	if(__builtin_expect(fd < 0, false)) return NULL;
+	return box_value(_cow_create_unboxed(fd, size));
 }
 
 inline internal void _cow_free_unboxed(const cow_t* cow)

src/cow.cpp

@@ -15,6 +15,7 @@ struct Cow::_inner {
 
 	~_inner();
 	_inner(size_t sz);
+	_inner(int fd, size_t sz);
 	_inner(cow_t* ptr);
 
 	_inner(const _inner& copy) = delete;
@@ -27,10 +28,12 @@ Cow::_inner::~_inner() {
 	_cow_free_unboxed(ptr());
 	cow.poisoned=true;
 }
-Cow::_inner::_inner(size_t sz) : cow(_cow_create_unboxed(sz)){
+Cow::_inner::_inner(int fd, size_t sz) : cow(_cow_create_unboxed(fd, sz)){
 	
 	if(UNLIKELY(cow.poisoned)) throw CowException(cow_err());
 }
+Cow::_inner::_inner(size_t sz) : _inner(-1, sz) {}
+
 Cow::_inner::_inner(cow_t* ptr) : cow(*ptr)
 {
 	free(ptr);
@@ -38,6 +41,7 @@ Cow::_inner::_inner(cow_t* ptr) : cow(*ptr)
 }
 
 Cow::Cow(size_t size) : super(std::make_shared<_inner>(size)){}
+Cow::Cow(int fd, size_t size) : super(std::make_shared<_inner>(fd, size)){}
 Cow::Cow(cow_t* raw) : super(std::make_shared<_inner>(raw)){}
 
 Cow::Cow(Cow&& m) : super(std::move(*const_cast<std::shared_ptr<_inner>*>(&m.super))){}

src/cow_t.h

@@ -44,7 +44,7 @@ _Static_assert
 		(offsetof(cow_t, size) == sizeof(void*), "`cow_t.size` should have an offset equal to `sizeof(void*)` or cow_size_unsafe() becomes UB.");
 #endif
 
-cow_t _cow_create_unboxed(size_t size) internal;
+cow_t _cow_create_unboxed(int rfd, size_t size) internal;
 void _cow_free_unboxed(const cow_t* cow) internal;
 
 #ifdef __cplusplus