trace logging with DEBUG or explicitly in release with COW_TRACE macro defs

include/cow.h

@@ -1,10 +1,15 @@
 #ifndef _COW_H
 #define _COW_H
 
+#ifdef __cplusplus
+#define restrict __restrict__
+extern "C" {
+#endif
+
 #include <stdlib.h>
 
 // Copy-on-write mapped memory.
-typedef struct cow cow_t, *cow;
+typedef struct cow cow_t;
 
 /// Create a new copy-on-write area of `size` bytes. 
 /// Writes to this instance pointer (`cow_ptr()`) are written to the allocated memory.
@@ -29,4 +34,9 @@ size_t cow_size(const cow_t* cow);
 //XXX: Too unsafe and not useful enough to warrant a function/macro.
 //#define cow_from_ptr(p) (cow_t*)(&(p))
 
+#ifdef __cplusplus
+#undef restrict
+}
+#endif
+
 #endif /* _COW_H */

src/cow.c

@@ -13,6 +13,12 @@
 
 #define box(t) aligned_alloc(_Alignof(t), sizeof(t))
 
+#if defined(DEBUG) || defined(COW_TRACE)
+#define TRACE(msg, ...) (fprintf(stderr, "[TRACE] %s->%s %d: " msg "\n", __FILE__, __func__, __LINE__, __VA_ARGS__), (void)0)
+#else
+#define TRACE(msg, ...) ((void)0)
+#endif
+
 struct cow {
 	void* origin; // ptr to mapped memory. This *MUST* be the first field and have an offset of 0.
 
@@ -31,6 +37,7 @@ static __attribute__((noreturn)) __attribute__((noinline)) __attribute__((cold))
 static inline cow_t* box_value(cow_t v)
 {
 	cow_t* boxed = box(cow_t);
+	TRACE("boxing cow_t { origin = %p, fd = 0x%x, size = %lu } -> %p (%lu bytes)", v.origin, v.fd, v.size, (const void*)boxed, sizeof(cow_t));
 	*boxed = v;
 	return boxed;
 }
@@ -74,11 +81,13 @@ cow_t* cow_create(size_t size)
 	ret.origin = mmap(NULL, size, PROT_READ|PROT_WRITE, MAP_SHARED, ret.fd, 0);
 	if(ret.origin == MAP_FAILED) die("cow_create:mmap");
 
+	TRACE("mapped new cow page of %lu size at %p (memfd %d)", size, ret.origin, ret.fd);
 	return box_value(ret);
 }
 
 void cow_free(cow_t* restrict cow)
 {
+	TRACE("unmapping %s cow of %lu size from %p (fd %d, real fd %d)", cow_is_fake(cow) ? "fake" : "and closing fd of origin", cow->size, cow->origin, cow->fd, cow_real_fd(cow));
 	munmap(cow->origin, cow->size);
 	if(!cow_is_fake(cow))
 		close(cow->fd);
@@ -94,5 +103,6 @@ cow_t* cow_clone(const cow_t* cow)
 	clone.fd = (~INT_MAX) | cow->fd;
 	clone.size = cow->size;
 
+	TRACE("mapped cloned cow page of %lu size from %p (%s) at %p (clone fd %d, parent fd %d, real fd %d)", clone.size, cow->origin, cow_is_fake(cow) ? "fake" : "origin", clone.origin, clone.fd, cow->fd, cow_real_fd(&clone));
 	return box_value(clone);
 }